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# FROM & JOIN Clause

## 1. Syntax Overview

```sql
FROM relation (',' relation)*

relation
    : relation joinType JOIN relation joinCriteria 
    | aliasedRelation
    ;

joinType
    : INNER?
    | OUTER?
    | CROSS?
    | ASOF?
    ;

joinCriteria
    : ON booleanExpression
    | USING '(' identifier (',' identifier)* ')'
    ;

aliasedRelation
    : relationPrimary (AS? identifier columnAliases?)?
    ;

columnAliases
    : '(' identifier (',' identifier)* ')'
    ;

relationPrimary
    : qualifiedName                                              #tableName
    | '(' query ')'                                              #subqueryRelation
    | '(' relation ')'                                           #parenthesizedRelation
    ;

qualifiedName
    : identifier ('.' identifier)*
    ;
```

## 2. FROM Clause Syntax

The `FROM` clause specifies the data sources for the query. Logically, query execution begins with the `FROM` clause. It can include a single table, a combination of multiple tables joined using `JOIN` clauses, or a subquery containing another `SELECT` query.

## 3. JOIN Clause

The `JOIN` clause combines two tables based on specific conditions, typically predicates, but other implicit rules can also apply.

In the current version of IoTDB, the following joins are supported:

1. **Inner Join**: The join condition can be any equality expression.
2. **Outer Join**: The join condition can be any equality expression.
3. **Cross Join**: Represents the Cartesian product of two tables.
4. ​**​ASOF JOIN​​** (AS OF a specific point in time) is a specialized join operation based on temporal or approximate matching conditions, designed for scenarios where timestamps between two datasets are not perfectly aligned. It matches each row from the left table with the closest corresponding row in the right table that meets the specified conditions (typically the nearest preceding or succeeding timestamp). This operation is widely used for time-series data analysis (e.g., sensor data, financial market feeds).

### 3.1 Inner Join

`INNER JOIN` can be written explicitly or implicitly by omitting the `INNER` keyword. It returns records where the join condition is satisfied.

#### 3.1.1 Explicit Join (Recommended)

Explicit joins use the syntax JOIN + ON or JOIN + USING to specify join conditions:

```sql
// Explicit join: Specify the join condition after the ON keyword or the join column(s) after the USING keyword.
SELECT selectExpr [, selectExpr] ... FROM <TABLE_NAME> [INNER] JOIN <TABLE_NAME> joinCriteria [WHERE whereCondition]

joinCriteria
    : ON booleanExpression
    | USING '(' identifier (',' identifier)* ')'
    ;  
```

**Note: Difference Between** **`USING`** **and** **`ON`**

- `USING` simplifies explicit join conditions by accepting a list of column names common to both tables. For example, `USING (time)` is equivalent to `ON (t1.time = t2.time)`. When using `USING`, there is logically one `time` column in the result.
- With `ON`, column names remain distinct (e.g., `t1.time` and `t2.time`).
- The final query result depends on the fields specified in the `SELECT` statement.


#### 3.1.2 Implicit Join

Implicit joins do not use `JOIN`, `ON`, or `USING` keywords. Instead, conditions are specified in the `WHERE` clause:

```sql
// Implicit join: Specify the join condition in the WHERE clause.
SELECT selectExpr [, selectExpr] ... FROM <TABLE_NAME> [, <TABLE_NAME>] ... [WHERE whereCondition] 
```

### 3.2 Outer Join

An **outer join** returns rows even when no matching records exist in the other table. Types include:

- **LEFT OUTER JOIN**: Returns all rows from the left table.
- **RIGHT OUTER JOIN**: Returns all rows from the right table.
- **FULL OUTER JOIN**: Returns all rows from both tables.

#### 3.2.1 Left Outer Join

LEFT [OUTER] JOIN (i.e., left outer join) returns all records from the left table, along with the records from the right table that satisfy the join condition with the left table. For records in the right table that have no matching entries in the left table, NULL values are returned. Since the LEFT JOIN keyword must be specified, left outer join typically uses only the explicit join syntax, where the join condition is specified after ON or USING.

> Supported in V2.0.5 and later versions

The SQL syntax is as follows:

```SQL
-- Explicit join: specify the join condition after the ON keyword or join columns after the USING keyword
SELECT selectExpr [, selectExpr] ... FROM <TABLE_NAME> LEFT [OUTER] JOIN <TABLE_NAME> joinCriteria [WHERE whereCondition]

joinCriteria
    : ON booleanExpression
    | USING '(' identifier (',' identifier)* ')'
    ;
```

#### 3.2.2 Right Outer Join

RIGHT [OUTER] JOIN (i.e., right outer join) returns all records from the right table, along with the records from the left table that satisfy the join condition with the right table. For records in the left table that have no matching entries in the right table, NULL values are returned.

> Supported in V2.0.5 and later versions

RIGHT JOIN is a "symmetric" operation to LEFT JOIN. In practice, `LEFT JOIN` is more commonly used because we usually care more about the data in the left table in real-world applications. Furthermore, `RIGHT JOIN` can always be converted to `LEFT JOIN` — the query result of `A RIGHT JOIN B ON A.id=B.id` is equivalent to that of `B LEFT JOIN A ON B.id = A.id`.

The SQL syntax is as follows:

```SQL
-- Specify the join condition after the ON keyword or join columns after the USING keyword
SELECT selectExpr [, selectExpr] ... FROM <TABLE_NAME> RIGHT [OUTER] JOIN <TABLE_NAME> joinCriteria [WHERE whereCondition]

joinCriteria
    : ON booleanExpression
    | USING '(' identifier (',' identifier)* ')'
    ;
```

#### 3.2.3 Full Outer Join

FULL [OUTER] JOIN (i.e., full outer join) returns all records from both tables. If a record in one table has no match in the other, `NULL` values are returned for the unmatched fields. `FULL JOIN` **must use explicit join conditions**.

```sql
//Specify the join condition after the ON keyword or specify the join columns after the USING keyword.
SELECT selectExpr [, selectExpr] ... FROM <TABLE_NAME> FULL [OUTER] JOIN <TABLE_NAME> joinCriteria [WHERE whereCondition]

joinCriteria
    : ON booleanExpression
    | USING '(' identifier (',' identifier)* ')'
    ;
```

### 3.3 Cross Join
A cross join represents the Cartesian product of two tables, returning all possible combinations of the N rows from the left table and the M rows from the right table, resulting in N*M rows. This type of join is the least commonly used in practice.

### 3.4 ​Asof Join

IoTDB ASOF JOIN is an approximate point join method that allows users to perform matching based on the closest timestamp according to specified rules. ​​The current version only supports ASOF INNER/LEFT JOIN.​​

> ASOF LEFT JOIN supported in V2.0.5 and later versions

The SQL syntax is as follows:

```SQL
SELECT selectExpr [, selectExpr] ... FROM 
<TABLE_NAME1> ASOF[(tolerance theta)] [INNER|LEFT] JOIN <TABLE_NAME2> joinCriteria 
[WHERE whereCondition]
WHERE a.time = tolerance(b.time, 1s)

joinCriteria
    : ON <TABLE_NAME1>.time comparisonOperator <TABLE_NAME2>.time 
    ;

comparisonOperator
    : < | <= | > | >=
    ;
```

**​Notes:​​**

* ASOF JOIN defaults to ASOF INNER JOIN implementation.
* When using the ON keyword for joining, the join condition must include an inequality join condition where both the left and right sides are of TIMESTAMP type (i.e., the primary join condition). Only four operators are supported: `">", ">=", "<", "<="`. The corresponding join matching rules are as follows (where lt represents the left table and rt represents the right table):

| Operator                   | Join Method                                   |
| -------------------------- | ---------------------------------------------- |
| `lt.time >= rt.time` | The closest timestamp in the left table that is greater than or equal to the right table's timestamp. |
| `lt.time > rt.time`  | The closest timestamp in the left table that is greater than the right table's timestamp.     |
| `lt.time <= rt.time` | The closest timestamp in the left table that is less than or equal to the right table's timestamp. |
| `lt.time < rt.time`  | The closest timestamp in the left table that is less than the right table's timestamp.     |

* `Tolerance parameter​`​: The maximum allowed time difference for searching data in the right table (expressed as a TimeDuration, e.g., 1d for one day). If the Tolerance parameter is not specified, the search time range defaults to ​​infinity​​. ​​Note​​: Currently, this parameter is only supported in ASOF ​​INNER​​ JOIN.
* In addition to the primary join condition, ASOF can also specify equality join conditions for other columns (ID, Attribute, Measurement), which means the query results are grouped by these other columns. The primary join condition must be placed ​**last**​, and it must be connected to other conditions (if any) using "AND".

### 3.5 Semi Join/Anti-Semi Join

A semi join is a special join operation whose purpose is to determine whether rows in one table exist in another table. The result set returned by a semi join contains rows from the first table that meet the join condition, but does not include the actual data from the second table. Corresponding to semi join is anti-semi join, which is used to identify rows that have no matches between two tables. The result set returned by an anti-semi join contains rows from the first table that satisfy the join condition, but excludes rows from the second table that match those rows.

In the IoTDB table model, the `SEMI JOIN` syntax is not provided; instead, IN subqueries or EXISTS subqueries are supported to implement semi joins. Similarly, the `ANTI SEMI JOIN` syntax is not provided, and NOT IN or NOT EXISTS subqueries are supported to implement anti-semi joins. For detailed explanations of subqueries, refer to [Nested Queries](../SQL-Manual/Nested-Queries.md).

* Examples of semi join syntax are as follows:

```SQL
-- Implement semi join using IN
SELECT *
FROM table1
WHERE time IN (SELECT time FROM table2);

-- Implement semi join using EXISTS
SELECT *
FROM table1 t1
WHERE EXISTS (SELECT 1 FROM table2 t2 WHERE t1.time = t2.time);

-- Equivalent to the SEMI JOIN syntax in other databases
SELECT table1.*
FROM table1 SEMI JOIN table2
ON table1.time=table2.time;
```

* Examples of anti-semi join syntax are as follows:

```SQL
-- Implement anti-semi join using NOT IN
SELECT *
FROM table1
WHERE time NOT IN (SELECT time FROM table2);

-- Implement anti-semi join using NOT EXISTS
SELECT *
FROM table1 t1
WHERE NOT EXISTS (SELECT 1 FROM table2 t2 WHERE t1.time = t2.time);

-- Equivalent to the ANTI SEMI JOIN syntax in other databases
SELECT table1.*
FROM table1 ANTI JOIN table2
ON table1.time=table2.time;
```


## 4. Example Queries

The [Example Data page](../Reference/Sample-Data.md)page provides SQL statements to construct table schemas and insert data. By downloading and executing these statements in the IoTDB CLI, you can import the data into IoTDB. This data can be used to test and run the example SQL queries included in this documentation, allowing you to reproduce the described results.

### 4.1 FROM Examples

#### 4.1.1 Query from a Single Table

**Example 1:** This query retrieves all records from `table1` and sorts them by time.

```sql
SELECT * FROM table1 ORDER BY time;
```

Query Results:

```sql
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                arrival_time|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-26T13:37:00.000+08:00|   BJ|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:37:34.000+08:00|
|2024-11-26T13:38:00.000+08:00|   BJ|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:38:25.000+08:00|
|2024-11-27T16:38:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    35.1|  true|2024-11-27T16:37:01.000+08:00|
|2024-11-27T16:39:00.000+08:00|   BJ|    1001|      101|       B|        180|       85.0|    35.3|  null|                         null|
|2024-11-27T16:40:00.000+08:00|   BJ|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:03.000+08:00|
|2024-11-27T16:41:00.000+08:00|   BJ|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:04.000+08:00|
|2024-11-27T16:42:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    35.2| false|                         null|
|2024-11-27T16:43:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    null| false|                         null|
|2024-11-27T16:44:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    null| false|2024-11-27T16:37:08.000+08:00|
|2024-11-28T08:00:00.000+08:00|   SH|    3001|      100|       C|         90|       85.0|    null|  null|2024-11-28T08:00:09.000+08:00|
|2024-11-28T09:00:00.000+08:00|   SH|    3001|      100|       C|         90|       null|    40.9|  true|                         null|
|2024-11-28T10:00:00.000+08:00|   SH|    3001|      100|       C|         90|       85.0|    35.2|  null|2024-11-28T10:00:11.000+08:00|
|2024-11-28T11:00:00.000+08:00|   SH|    3001|      100|       C|         90|       88.0|    45.1|  true|2024-11-28T11:00:12.000+08:00|
|2024-11-29T10:00:00.000+08:00|   SH|    3001|      101|       D|        360|       85.0|    null|  null|2024-11-29T10:00:13.000+08:00|
|2024-11-29T11:00:00.000+08:00|   SH|    3002|      100|       E|        180|       null|    45.1|  true|                         null|
|2024-11-29T18:30:00.000+08:00|   SH|    3002|      100|       E|        180|       90.0|    35.4|  true|2024-11-29T18:30:15.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T14:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 18
It costs 0.085s
```

**Example 2:** This query retrieves all records from `table1` where the device is `101` and sorts them by time.

```sql
SELECT * FROM table1 t1 where t1.device_id='101' order by time;
```

Query Results:

```sql
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                arrival_time|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-27T16:38:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    35.1|  true|2024-11-27T16:37:01.000+08:00|
|2024-11-27T16:39:00.000+08:00|   BJ|    1001|      101|       B|        180|       85.0|    35.3|  null|                         null|
|2024-11-27T16:40:00.000+08:00|   BJ|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:03.000+08:00|
|2024-11-27T16:41:00.000+08:00|   BJ|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-27T16:37:04.000+08:00|
|2024-11-27T16:42:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    35.2| false|                         null|
|2024-11-27T16:43:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    null| false|                         null|
|2024-11-27T16:44:00.000+08:00|   BJ|    1001|      101|       B|        180|       null|    null| false|2024-11-27T16:37:08.000+08:00|
|2024-11-29T10:00:00.000+08:00|   SH|    3001|      101|       D|        360|       85.0|    null|  null|2024-11-29T10:00:13.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T14:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 10
It costs 0.061s
```

#### 4.1.2 Querying from a Subquery

**Example 1:** This query retrieves the total number of records in `table1`.

```sql
SELECT COUNT(*) AS count FROM (SELECT * FROM table1);
```

Query Results:

```sql
+-----+
|count|
+-----+
|   18|
+-----+
Total line number = 1
It costs 0.072s
```

### 4.2 JOIN Examples

#### 4.2.1 Inner Join

**Example 1: Explicit Join using `ON`** 

This query retrieves records where `table1` and `table2` share the same `time` values.

```sql
SELECT 
  t1.time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2 
FROM 
  table1 t1 JOIN table2 t2 
ON t1.time = t2.time
```

Query Results:

```sql
+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 3
It costs 0.076s
```

**Example 2: Explicit Join using `USING`** 

This query retrieves records from `table1` and `table2`, joining on the `time` column.

```sql
SELECT time,
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2   
FROM 
  table1 t1 JOIN table2 t2
USING(time)
```

Query Results:

```sql
+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 3
It costs 0.081s
```

**Example 3: Implicit Join using `WHERE`** 

This query joins `table1` and `table2` by specifying the condition in the `WHERE` clause.

```sql
SELECT t1.time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2 
FROM 
table1 t1, table2 t2
WHERE
t1.time=t2.time
```

Query Results:

```sql
+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 3
It costs 0.082s
```

**Example 4: Equality Join on Non-time Columns**

```SQL
SELECT 
  t1.time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2 
FROM 
  table1 t1 JOIN table2 t2 
ON t1.device_id = t2.device_id 
ORDER BY t1.time
LIMIT 10
```

Query Results:

```SQL
+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        null|
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        85.0|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|    100|        null|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|    100|        85.0|
|2024-11-27T16:38:00.000+08:00|    101|        null|    101|        90.0|
|2024-11-27T16:38:00.000+08:00|    101|        null|    101|        85.0|
|2024-11-27T16:38:00.000+08:00|    101|        null|    101|        85.0|
|2024-11-27T16:39:00.000+08:00|    101|        85.0|    101|        90.0|
+-----------------------------+-------+------------+-------+------------+
Total line number = 10
It costs 0.030s
```


#### 4.2.2 Outer Join

1. LEFT JOIN

**Example 1: Explicit Join**

```SQL
SELECT 
  t1.time as time1, t2.time as time2, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 LEFT JOIN table2 t2 
ON t1.time = t2.time
```

Query Results:

```SQL
+-----------------------------+-----------------------------+-------+------------+-------+------------+
|                        time1|                        time2|device1|temperature1|device2|temperature2|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|                         null|    100|        90.0|   null|        null|
|2024-11-27T16:38:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:39:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:40:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:41:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:42:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:43:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:44:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-28T08:00:00.000+08:00|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|                         null|    100|        null|   null|        null|
|2024-11-28T10:00:00.000+08:00|                         null|    100|        85.0|   null|        null|
|2024-11-28T11:00:00.000+08:00|                         null|    100|        88.0|   null|        null|
|2024-11-29T10:00:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-29T11:00:00.000+08:00|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|2024-11-29T18:30:00.000+08:00|                         null|    100|        90.0|   null|        null|
|2024-11-30T09:30:00.000+08:00|                         null|    101|        90.0|   null|        null|
|2024-11-30T14:30:00.000+08:00|                         null|    101|        90.0|   null|        null|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
Total line number = 18
It costs 0.031s
```

**Example 2: Explicit Join**

```SQL
SELECT 
  time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 LEFT JOIN table2 t2 
USING(time)
```

Query Results:

```SQL
+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|   null|        null|
|2024-11-27T16:38:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:39:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:40:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:41:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:42:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:43:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:44:00.000+08:00|    101|        null|   null|        null|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|    100|        null|   null|        null|
|2024-11-28T10:00:00.000+08:00|    100|        85.0|   null|        null|
|2024-11-28T11:00:00.000+08:00|    100|        88.0|   null|        null|
|2024-11-29T10:00:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|2024-11-29T18:30:00.000+08:00|    100|        90.0|   null|        null|
|2024-11-30T09:30:00.000+08:00|    101|        90.0|   null|        null|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|   null|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 18
It costs 0.031s
```

**Example 3: Join Condition on Non-time Column**

```SQL
SELECT 
  region,
  t1.time as time1,
  t1.temperature as temperature1, 
  t2.time as time2, 
  t2.temperature as temperature2 
FROM 
  table1 t1 LEFT JOIN table2 t2 
USING(region)
LIMIT 10
```

Query Results:

```SQL
+------+-----------------------------+------------+-----------------------------+------------+
|region|                        time1|temperature1|                        time2|temperature2|
+------+-----------------------------+------------+-----------------------------+------------+
|Shanghai|2024-11-29T11:00:00.000+08:00|        null|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-29T11:00:00.000+08:00|        null|2024-11-28T08:00:00.000+08:00|        85.0|
|Shanghai|2024-11-29T11:00:00.000+08:00|        null|2024-11-30T00:00:00.000+08:00|        90.0|
|Shanghai|2024-11-29T11:00:00.000+08:00|        null|2024-11-29T00:00:00.000+08:00|        85.0|
|Shanghai|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-28T08:00:00.000+08:00|        85.0|
|Shanghai|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-30T00:00:00.000+08:00|        90.0|
|Shanghai|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-29T00:00:00.000+08:00|        85.0|
|Shanghai|2024-11-29T18:30:00.000+08:00|        90.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-29T18:30:00.000+08:00|        90.0|2024-11-28T08:00:00.000+08:00|        85.0|
+------+-----------------------------+------------+-----------------------------+------------+
Total line number = 10
It costs 0.038s
```

2. RIGHT JOIN

**Example 1: Explicit Join**

```SQL
SELECT 
  t1.time as time1, t2.time as time2, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 RIGHT JOIN table2 t2 
ON t1.time = t2.time
```

Query Results:

```SQL
+-----------------------------+-----------------------------+-------+------------+-------+------------+
|                        time1|                        time2|device1|temperature1|device2|temperature2|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|                         null|2024-11-27T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-28T08:00:00.000+08:00|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|                         null|2024-11-29T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-29T11:00:00.000+08:00|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|                         null|2024-11-30T00:00:00.000+08:00|   null|        null|    101|        90.0|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
Total line number = 6
It costs 0.030s
```

**Example 2: Explicit Join**

```SQL
SELECT 
  time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 RIGHT JOIN table2 t2 
USING(time)
```

Query Results:

```SQL
+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-27T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-29T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|2024-11-30T00:00:00.000+08:00|   null|        null|    101|        90.0|
+-----------------------------+-------+------------+-------+------------+
Total line number = 6
It costs 0.053s
```

**Example 3: Join Condition on Non-time Column**

```SQL
SELECT 
  region,
  t1.time as time1,
  t1.temperature as temperature1, 
  t2.time as time2, 
  t2.temperature as temperature2 
FROM 
  table1 t1 RIGHT JOIN table2 t2 
USING(region)
LIMIT 10
```

Query Results:

```SQL
+------+-----------------------------+------------+-----------------------------+------------+
|region|                        time1|temperature1|                        time2|temperature2|
+------+-----------------------------+------------+-----------------------------+------------+
|Shanghai|2024-11-29T11:00:00.000+08:00|        null|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-29T18:30:00.000+08:00|        90.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-28T08:00:00.000+08:00|        85.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-30T14:30:00.000+08:00|        90.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-29T10:00:00.000+08:00|        85.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-28T09:00:00.000+08:00|        null|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-28T10:00:00.000+08:00|        85.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-28T11:00:00.000+08:00|        88.0|2024-11-29T11:00:00.000+08:00|        null|
|Shanghai|2024-11-29T11:00:00.000+08:00|        null|2024-11-28T08:00:00.000+08:00|        85.0|
+------+-----------------------------+------------+-----------------------------+------------+
Total line number = 10
It costs 0.029s
```

3. FULL JOIN

**Example 1: Full Outer Join using `ON`** 

This query retrieves all records from `table1` and `table2`, including unmatched rows with `NULL` values.

```sql
SELECT 
  t1.time as time1, t2.time as time2, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 FULL JOIN table2 t2 
ON t1.time = t2.time
```

Query Results:

```sql
+-----------------------------+-----------------------------+-------+------------+-------+------------+
|                        time1|                        time2|device1|temperature1|device2|temperature2|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|                         null|    100|        90.0|   null|        null|
|                         null|2024-11-27T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-27T16:38:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:39:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:40:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:41:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-27T16:42:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:43:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-27T16:44:00.000+08:00|                         null|    101|        null|   null|        null|
|2024-11-28T08:00:00.000+08:00|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|                         null|    100|        null|   null|        null|
|2024-11-28T10:00:00.000+08:00|                         null|    100|        85.0|   null|        null|
|2024-11-28T11:00:00.000+08:00|                         null|    100|        88.0|   null|        null|
|                         null|2024-11-29T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-29T10:00:00.000+08:00|                         null|    101|        85.0|   null|        null|
|2024-11-29T11:00:00.000+08:00|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|2024-11-29T18:30:00.000+08:00|                         null|    100|        90.0|   null|        null|
|                         null|2024-11-30T00:00:00.000+08:00|   null|        null|    101|        90.0|
|2024-11-30T09:30:00.000+08:00|                         null|    101|        90.0|   null|        null|
|2024-11-30T14:30:00.000+08:00|                         null|    101|        90.0|   null|        null|
+-----------------------------+-----------------------------+-------+------------+-------+------------+
Total line number = 21
It costs 0.071s
```

**Example 2: Explicit Join using `USING`**

This query retrieves all records from `table1` and `table2`, combining them based on the `time` column. Rows with no matches in one of the tables will include `NULL` values for the missing fields.

```sql
SELECT 
  time, 
  t1.device_id as device1, 
  t1.temperature as temperature1, 
  t2.device_id as device2, 
  t2.temperature as temperature2  
FROM 
  table1 t1 FULL JOIN table2 t2 
USING(time)
```

Query Results:

```sql
+-----------------------------+-------+------------+-------+------------+
|                         time|device1|temperature1|device2|temperature2|
+-----------------------------+-------+------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|   null|        null|
|2024-11-27T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-27T16:38:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:39:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:40:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:41:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-27T16:42:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:43:00.000+08:00|    101|        null|   null|        null|
|2024-11-27T16:44:00.000+08:00|    101|        null|   null|        null|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|    100|        null|   null|        null|
|2024-11-28T10:00:00.000+08:00|    100|        85.0|   null|        null|
|2024-11-28T11:00:00.000+08:00|    100|        88.0|   null|        null|
|2024-11-29T00:00:00.000+08:00|   null|        null|    101|        85.0|
|2024-11-29T10:00:00.000+08:00|    101|        85.0|   null|        null|
|2024-11-29T11:00:00.000+08:00|    100|        null|    100|        null|
|2024-11-29T18:30:00.000+08:00|    100|        90.0|   null|        null|
|2024-11-30T00:00:00.000+08:00|   null|        null|    101|        90.0|
|2024-11-30T09:30:00.000+08:00|    101|        90.0|   null|        null|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|   null|        null|
+-----------------------------+-------+------------+-------+------------+
Total line number = 21
It costs 0.073s
```

Example 3: The join condition is based on a non-time column.

```sql
SELECT 
  region,
  t1.time as time1,
  t1.temperature as temperature1, 
  t2.time as time2, 
  t2.temperature as temperature2 
FROM 
  table1 t1 FULL JOIN table2 t2 
USING(region)
LIMIT 10
```

Query Results:

```sql
+------+-----------------------------+------------+-----------------------------+------------+
|region|                        time1|temperature1|                        time2|temperature2|
+------+-----------------------------+------------+-----------------------------+------------+
|  上海|2024-11-29T11:00:00.000+08:00|        null|2024-11-29T11:00:00.000+08:00|        null|
|  上海|2024-11-29T11:00:00.000+08:00|        null|2024-11-28T08:00:00.000+08:00|        85.0|
|  上海|2024-11-29T11:00:00.000+08:00|        null|2024-11-30T00:00:00.000+08:00|        90.0|
|  上海|2024-11-29T11:00:00.000+08:00|        null|2024-11-29T00:00:00.000+08:00|        85.0|
|  上海|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-29T11:00:00.000+08:00|        null|
|  上海|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-28T08:00:00.000+08:00|        85.0|
|  上海|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-30T00:00:00.000+08:00|        90.0|
|  上海|2024-11-30T09:30:00.000+08:00|        90.0|2024-11-29T00:00:00.000+08:00|        85.0|
|  上海|2024-11-29T18:30:00.000+08:00|        90.0|2024-11-29T11:00:00.000+08:00|        null|
|  上海|2024-11-29T18:30:00.000+08:00|        90.0|2024-11-28T08:00:00.000+08:00|        85.0|
+------+-----------------------------+------------+-----------------------------+------------+
Total line number = 10
It costs 0.040s
```

#### 4.2.3 Cross Join

**Example 1: Explicit Join**

```sql
SELECT table1.*, table2.* FROM table1 CROSS JOIN table2 LIMIT 8;
```

Query Results:

```sql
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                 arrival_time|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                 arrival_time|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-30T00:00:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-29T00:00:00.000+08:00|  上海|    3001|      101|       D|        360|       85.0|    35.1|  null|2024-11-29T10:00:13.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-27T00:00:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    35.1|  true|2024-11-27T16:37:01.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-29T11:00:00.000+08:00|  上海|    3002|      100|       E|        180|       null|    45.1|  true|                         null|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-28T08:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    35.2| false|2024-11-28T08:00:09.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-26T13:37:00.000+08:00|  北京|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:37:34.000+08:00|
|2024-11-30T14:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|2024-11-30T00:00:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T14:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|2024-11-29T00:00:00.000+08:00|  上海|    3001|      101|       D|        360|       85.0|    35.1|  null|2024-11-29T10:00:13.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 8
It costs 0.282s
```

**Example 2: Implicit Join**

```sql
SELECT table1.*, table2.* FROM table1, table2 LIMIT 8;
```

Query Results:

```sql
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                 arrival_time|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                 arrival_time|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-30T00:00:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-29T00:00:00.000+08:00|  上海|    3001|      101|       D|        360|       85.0|    35.1|  null|2024-11-29T10:00:13.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-27T00:00:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    35.1|  true|2024-11-27T16:37:01.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-29T11:00:00.000+08:00|  上海|    3002|      100|       E|        180|       null|    45.1|  true|                         null|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-28T08:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    35.2| false|2024-11-28T08:00:09.000+08:00|
|2024-11-30T09:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|2024-11-26T13:37:00.000+08:00|  北京|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:37:34.000+08:00|
|2024-11-30T14:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|2024-11-30T00:00:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-30T14:30:00.000+08:00|   SH|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|2024-11-29T00:00:00.000+08:00|  上海|    3001|      101|       D|        360|       85.0|    35.1|  null|2024-11-29T10:00:13.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 8
It costs 0.047s
```

#### 4.2.4 Asof join

1. ASOF INNER JOIN

​​Example 1​​: Without specifying the tolerance parameter, where the timestamp in table1 is greater than or equal to and closest to the timestamp in table2.

```SQL
SELECT t1.time as time1, t1.device_id as device1, t1.temperature as temperature1, t2.time as time2, t2.device_id as device2, t2.temperature as temperature2 FROM  table1 t1 ASOF JOIN table2 t2 ON t1.time>=t2.time;
```

Query Results:

```SQL
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|                        time1|device1|temperature1|                        time2|device2|temperature2|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-30T00:00:00.000+08:00|    101|        90.0|
|2024-11-30T09:30:00.000+08:00|    101|        90.0|2024-11-30T00:00:00.000+08:00|    101|        90.0|
|2024-11-29T18:30:00.000+08:00|    100|        90.0|2024-11-29T11:00:00.000+08:00|    100|        null|
|2024-11-29T11:00:00.000+08:00|    100|        null|2024-11-29T11:00:00.000+08:00|    100|        null|
|2024-11-29T10:00:00.000+08:00|    101|        85.0|2024-11-29T00:00:00.000+08:00|    101|        85.0|
|2024-11-28T11:00:00.000+08:00|    100|        88.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-28T10:00:00.000+08:00|    100|        85.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|    100|        null|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-27T16:44:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:43:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:42:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:41:00.000+08:00|    101|        85.0|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:40:00.000+08:00|    101|        85.0|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:39:00.000+08:00|    101|        85.0|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:38:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|2024-11-26T13:37:00.000+08:00|    100|        90.0|
|2024-11-26T13:37:00.000+08:00|    100|        90.0|2024-11-26T13:37:00.000+08:00|    100|        90.0|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
```

Example 2​​: With the tolerance parameter specified, where the timestamp in table1 is greater than or equal to and closest to the timestamp in table2.

```SQL
SELECT t1.time as time1, t1.device_id as device1, t1.temperature as temperature1, t2.time as time2, t2.device_id as device2, t2.temperature as temperature2 FROM table1 t1 ASOF(tolerance 2s) JOIN table2 t2 ON t1.time>=t2.time;
```

Query Results:

```SQL
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|                        time1|device1|temperature1|                        time2|device2|temperature2|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|2024-11-29T11:00:00.000+08:00|    100|        null|2024-11-29T11:00:00.000+08:00|    100|        null|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-26T13:37:00.000+08:00|    100|        90.0|2024-11-26T13:37:00.000+08:00|    100|        90.0|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
```

**Example 3: Tolerance Parameter Specified, plant\_id is the Same, and the Timestamp in table1 is Greater Than or Equal to That in table2 with the Closest Timestamp**

```SQL
SELECT t1.time as time1, t1.plant_id as plant1, t1.temperature as temperature1, t2.time as time2, t2.plant_id as plant2, t2.temperature as temperature2 FROM table1 t1 ASOF(tolerance 2s) JOIN table2 t2 ON t1.plant_id=t2.plant_id and t1.time>=t2.time;
```

Query Results

```SQL
+-----------------------------+------+------------+-----------------------------+------+------------+
|                        time1|plant1|temperature1|                        time2|plant2|temperature2|
+-----------------------------+------+------------+-----------------------------+------+------------+
|2024-11-26T13:37:00.000+08:00|  1001|        90.0|2024-11-26T13:37:00.000+08:00|  1001|        90.0|
|2024-11-28T08:00:00.000+08:00|  3001|        85.0|2024-11-28T08:00:00.000+08:00|  3001|        85.0|
|2024-11-29T11:00:00.000+08:00|  3002|        null|2024-11-29T11:00:00.000+08:00|  3002|        null|
+-----------------------------+------+------------+-----------------------------+------+------------+
Total line number = 3
It costs 0.046s
```

**Example 4: Asof Join Between a Time Period Today and the Corresponding Time Period Last Week**

```SQL
SELECT * FROM   (SELECT time, device_id AS device1, temperature AS temperature1  FROM table1 ) AS t1 ASOF JOIN   (SELECT time,  device_id AS device2,  temperature AS temperature2  FROM table1) AS t2 ON t1.time>date_bin(1w, t2.time) limit 10
```

Query Results:

```SQL
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|                         time|device1|temperature1|                         time|device2|temperature2|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-29T11:00:00.000+08:00|    100|        null|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-30T09:30:00.000+08:00|    101|        90.0|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-29T18:30:00.000+08:00|    100|        90.0|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-30T14:30:00.000+08:00|    101|        90.0|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-29T10:00:00.000+08:00|    101|        85.0|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-28T09:00:00.000+08:00|    100|        null|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-28T10:00:00.000+08:00|    100|        85.0|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-28T11:00:00.000+08:00|    100|        88.0|
|2024-11-30T09:30:00.000+08:00|    101|        90.0|2024-11-29T11:00:00.000+08:00|    100|        null|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
```

2. ASOF LEFT JOIN

**Example 1: The Timestamp in table1 is Greater Than or Equal to That in table2 with the Closest Timestamp**

```SQL
SELECT t1.time as time1, t1.device_id as device1, t1.temperature as temperature1, t2.time as time2, t2.device_id as device2, t2.temperature as temperature2 FROM  table1 t1 ASOF LEFT JOIN table2 t2 ON t1.time>=t2.time order by time1;
```

Query Results

```SQL
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|                        time1|device1|temperature1|                        time2|device2|temperature2|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
|2024-11-26T13:37:00.000+08:00|    100|        90.0|2024-11-26T13:37:00.000+08:00|    100|        90.0|
|2024-11-26T13:38:00.000+08:00|    100|        90.0|2024-11-26T13:37:00.000+08:00|    100|        90.0|
|2024-11-27T16:38:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:39:00.000+08:00|    101|        85.0|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:40:00.000+08:00|    101|        85.0|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:41:00.000+08:00|    101|        85.0|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:42:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:43:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-27T16:44:00.000+08:00|    101|        null|2024-11-27T00:00:00.000+08:00|    101|        85.0|
|2024-11-28T08:00:00.000+08:00|    100|        85.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-28T09:00:00.000+08:00|    100|        null|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-28T10:00:00.000+08:00|    100|        85.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-28T11:00:00.000+08:00|    100|        88.0|2024-11-28T08:00:00.000+08:00|    100|        85.0|
|2024-11-29T10:00:00.000+08:00|    101|        85.0|2024-11-29T00:00:00.000+08:00|    101|        85.0|
|2024-11-29T11:00:00.000+08:00|    100|        null|2024-11-29T11:00:00.000+08:00|    100|        null|
|2024-11-29T18:30:00.000+08:00|    100|        90.0|2024-11-29T11:00:00.000+08:00|    100|        null|
|2024-11-30T09:30:00.000+08:00|    101|        90.0|2024-11-30T00:00:00.000+08:00|    101|        90.0|
|2024-11-30T14:30:00.000+08:00|    101|        90.0|2024-11-30T00:00:00.000+08:00|    101|        90.0|
+-----------------------------+-------+------------+-----------------------------+-------+------------+
Total line number = 18
It costs 0.058s
```

**Example 2: plant\_id is the Same, and the Timestamp in table1 is Greater Than or Equal to That in table2 with the Closest Timestamp**


```SQL
SELECT t1.time as time1, t1.plant_id as plant1, t1.temperature as temperature1, t2.time as time2, t2.plant_id as plant2, t2.temperature as temperature2 FROM table1 t1 ASOF LEFT JOIN table2 t2 ON t1.plant_id=t2.plant_id and t1.time>=t2.time ORDER BY time1;
```

Query Results

```SQL
+-----------------------------+------+------------+-----------------------------+------+------------+
|                        time1|plant1|temperature1|                        time2|plant2|temperature2|
+-----------------------------+------+------------+-----------------------------+------+------------+
|2024-11-26T13:37:00.000+08:00|  1001|        90.0|2024-11-26T13:37:00.000+08:00|  1001|        90.0|
|2024-11-26T13:38:00.000+08:00|  1001|        90.0|2024-11-26T13:37:00.000+08:00|  1001|        90.0|
|2024-11-27T16:38:00.000+08:00|  1001|        null|2024-11-27T00:00:00.000+08:00|  1001|        85.0|
|2024-11-27T16:39:00.000+08:00|  1001|        85.0|2024-11-27T00:00:00.000+08:00|  1001|        85.0|
|2024-11-27T16:40:00.000+08:00|  1001|        85.0|2024-11-27T00:00:00.000+08:00|  1001|        85.0|
|2024-11-27T16:41:00.000+08:00|  1001|        85.0|2024-11-27T00:00:00.000+08:00|  1001|        85.0|
|2024-11-27T16:42:00.000+08:00|  1001|        null|2024-11-27T00:00:00.000+08:00|  1001|        85.0|
|2024-11-27T16:43:00.000+08:00|  1001|        null|2024-11-27T00:00:00.000+08:00|  1001|        85.0|
|2024-11-27T16:44:00.000+08:00|  1001|        null|2024-11-27T00:00:00.000+08:00|  1001|        85.0|
|2024-11-28T08:00:00.000+08:00|  3001|        85.0|2024-11-28T08:00:00.000+08:00|  3001|        85.0|
|2024-11-28T09:00:00.000+08:00|  3001|        null|2024-11-28T08:00:00.000+08:00|  3001|        85.0|
|2024-11-28T10:00:00.000+08:00|  3001|        85.0|2024-11-28T08:00:00.000+08:00|  3001|        85.0|
|2024-11-28T11:00:00.000+08:00|  3001|        88.0|2024-11-28T08:00:00.000+08:00|  3001|        85.0|
|2024-11-29T10:00:00.000+08:00|  3001|        85.0|2024-11-29T00:00:00.000+08:00|  3001|        85.0|
|2024-11-29T11:00:00.000+08:00|  3002|        null|2024-11-29T11:00:00.000+08:00|  3002|        null|
|2024-11-29T18:30:00.000+08:00|  3002|        90.0|2024-11-29T11:00:00.000+08:00|  3002|        null|
|2024-11-30T09:30:00.000+08:00|  3002|        90.0|2024-11-30T00:00:00.000+08:00|  3002|        90.0|
|2024-11-30T14:30:00.000+08:00|  3002|        90.0|2024-11-30T00:00:00.000+08:00|  3002|        90.0|
+-----------------------------+------+------------+-----------------------------+------+------------+
Total line number = 18
It costs 0.022s
```