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# Metadata Operations

## 1. Database Management

### 1.1 Create Database

**Syntax:**

```SQL
CREATE DATABASE (IF NOT EXISTS)? <DATABASE_NAME> (WITH properties)?
```

[Detailed syntax reference](../Basic-Concept/Database-Management_apache.md#_1-1-create-a-database)

**Examples:**

```SQL
CREATE DATABASE database1;
CREATE DATABASE IF NOT EXISTS database1;

-- Create database with 1-year TTL
CREATE DATABASE IF NOT EXISTS database1 with(TTL=31536000000);
```

### 1.2 Use Database

**Syntax:**

```SQL
USE <DATABASE_NAME>
```

**Examples:**

```SQL
USE database1
```

### 1.3 View Current Database

**Syntax:**

```SQL
SHOW CURRENT_DATABASE
```

**Examples:**

```SQL
IoTDB> SHOW CURRENT_DATABASE;
+---------------+
|CurrentDatabase|
+---------------+
|           null|
+---------------+

IoTDB> USE test;

IoTDB> SHOW CURRENT_DATABASE;
+---------------+
|CurrentDatabase|
+---------------+
|   iot_database|
+---------------+
```

### 1.4 List All Databases

**Syntax:**

```SQL
SHOW DATABASES (DETAILS)?
```

[Detailed syntax reference](../Basic-Concept/Database-Management_apache.md#_1-4-view-all-databases)

**Examples:**

```SQL
IoTDB> show databases
+---------+-------+-----------------------+---------------------+---------------------+
| Database|TTL(ms)|SchemaReplicationFactor|DataReplicationFactor|TimePartitionInterval|
+---------+-------+-----------------------+---------------------+---------------------+
|test_prop|    300|                      3|                    2|               100000|
|    test2|    300|                      3|                    2|            604800000|
+---------+-------+-----------------------+---------------------+---------------------+
IoTDB> show databases details
+---------+-------+-----------------------+---------------------+---------------------+-----------------------+-----------------------+
| Database|TTL(ms)|SchemaReplicationFactor|DataReplicationFactor|TimePartitionInterval|SchemaRegionGroupNum|  DataRegionGroupNum|
+---------+-------+-----------------------+---------------------+---------------------+-----------------------+-----------------------+
|test_prop|    300|                      3|                    2|               100000|                      1|                      2|
|    test2|    300|                      3|                    2|            604800000|                      1|                      2|
+---------+-------+-----------------------+---------------------+---------------------+-----------------------+-----------------------+
```

### 1.5 Modify Database

**Syntax:**

```SQL
ALTER DATABASE (IF EXISTS)? database=identifier SET PROPERTIES propertyAssignments
```

**Examples:**

```SQL
ALTER DATABASE database1 SET PROPERTIES TTL=31536000000;
```

### 1.6 Drop Database

**Syntax:**

```SQL
DROP DATABASE (IF EXISTS)? <DATABASE_NAME>
```

**Examples:**

```SQL
DROP DATABASE IF EXISTS database1
```

## 2. Table Management

### 2.1 Create Table

**Syntax:**

```SQL
createTableStatement
    : CREATE TABLE (IF NOT EXISTS)? qualifiedName
        '(' (columnDefinition (',' columnDefinition)*)? ')'
        charsetDesc?
        comment?
        (WITH properties)?
     ;

charsetDesc
    : DEFAULT? (CHAR SET | CHARSET | CHARACTER SET) EQ? identifierOrString
    ;

columnDefinition
    : identifier columnCategory=(TAG | ATTRIBUTE | TIME) charsetName? comment?
    | identifier type (columnCategory=(TAG | ATTRIBUTE | TIME | FIELD))? charsetName? comment?
    ;

charsetName
    : CHAR SET identifier
    | CHARSET identifier
    | CHARACTER SET identifier
    ;

comment
    : COMMENT string
    ;
```

[Detailed syntax reference](../Basic-Concept/Table-Management_apache.md#_1-1-create-a-table)

**Examples:**

```SQL
CREATE TABLE table1 (
  time TIMESTAMP TIME,
  region STRING TAG,
  plant_id STRING TAG,
  device_id STRING TAG,
  model_id STRING ATTRIBUTE,
  maintenance STRING ATTRIBUTE COMMENT 'maintenance',
  temperature FLOAT FIELD COMMENT 'temperature',
  humidity FLOAT FIELD COMMENT 'humidity',
  status BOOLEAN FIELD COMMENT 'status',
  arrival_time TIMESTAMP FIELD COMMENT 'arrival_time'
) COMMENT 'table1' WITH (TTL=31536000000);

CREATE TABLE IF NOT EXISTS table2 ();

CREATE TABLE tableC (
  "plant" STRING TAG,
  "temperature" INT32 FIELD COMMENT 'temperature'
) WITH (TTL=DEFAULT);
```

### 2.2 List Tables

**Syntax:**

```SQL
SHOW TABLES (DETAILS)? ((FROM | IN) database_name)?
```

**Examples:**

```SQL
IoTDB> show tables from test_db
+---------+-------+-------+
|TableName|TTL(ms)|Comment|
+---------+-------+-------+
|     test|    INF|   TEST|
+---------+-------+-------+

IoTDB> show tables details from test_db
+---------+-------+----------+-------+
|TableName|TTL(ms)|    Status|Comment|
+---------+-------+----------+-------+
|     test|    INF|     USING|   TEST|
|  turbine|    INF|PRE_CREATE|   null|
|      car|   1000|PRE_DELETE|   null|
+---------+-------+----------+-------+
```

### 2.3 Describe Table Columns

**Syntax:**

```SQL
(DESC | DESCRIBE) <TABLE_NAME> (DETAILS)?
```

**Examples:**

```SQL
IoTDB> desc tableB
+----------+---------+-----------+-------+
|ColumnName| DataType|   Category|Comment|
+----------+---------+-----------+-------+
|      time|TIMESTAMP|       TIME|   null|
|         a|   STRING|        TAG|      a|
|         b|   STRING|  ATTRIBUTE|      b|
|         c|    INT32|      FIELD|      c|
+----------+---------+-----------+-------+

IoTDB> desc tableB details
+----------+---------+-----------+----------+-------+
|ColumnName| DataType|   Category|    Status|Comment|
+----------+---------+-----------+----------+-------+
|      time|TIMESTAMP|       TIME|     USING|   null|
|         a|   STRING|        TAG|     USING|      a|
|         b|   STRING|  ATTRIBUTE|     USING|      b|
|         c|    INT32|      FIELD|     USING|      c|
|         d|    INT32|      FIELD|PRE_DELETE|      d|
+----------+---------+-----------+----------+-------+
```

### 2.4 Modify Table

**Syntax:**

```SQL
ALTER TABLE (IF EXISTS)? tableName=qualifiedName ADD COLUMN (IF NOT EXISTS)? column=columnDefinition COMMENT 'column_comment'               #addColumn
| ALTER TABLE (IF EXISTS)? tableName=qualifiedName DROP COLUMN (IF EXISTS)? column=identifier                    #dropColumn
// set TTL can use this
| ALTER TABLE (IF EXISTS)? tableName=qualifiedName SET PROPERTIES propertyAssignments                #setTableProperties
| COMMENT ON TABLE tableName=qualifiedName IS 'table_comment'
| COMMENT ON COLUMN tableName.column IS 'column_comment'
```

**Examples:**

```SQL
ALTER TABLE tableB ADD COLUMN IF NOT EXISTS a TAG COMMENT 'a'
ALTER TABLE tableB set properties TTL=3600
COMMENT ON TABLE table1 IS 'table1'
COMMENT ON COLUMN table1.a IS null
```

### 2.5 Drop Table

**Syntax:**

```SQL
DROP TABLE (IF EXISTS)? <TABLE_NAME>
```

**Examples:**

```SQL
DROP TABLE tableA
DROP TABLE test.tableB
```