docs/zh/UserGuide/Operators-Functions/Conversion.md

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## 数据类型转换

### CAST

#### 函数简介

当前 IoTDB 支持6种数据类型，其中包括 INT32、INT64、FLOAT、DOUBLE、BOOLEAN 以及 TEXT。当我们对数据进行查询或者计算时可能需要进行数据类型的转换， 比如说将 TEXT 转换为 INT32，或者提高数据精度，比如说将 FLOAT 转换为 DOUBLE。IoTDB 支持使用cast 函数对数据类型进行转换。

语法示例如下：

```sql
SELECT cast(s1 as INT32) from root.sg
```

cast 函数语法形式上与 PostgreSQL 一致，AS 后指定的数据类型表明要转换成的目标类型，目前 IoTDB 支持的六种数据类型均可以在 cast 函数中使用，遵循的转换规则如下表所示，其中行表示原始数据类型，列表示要转化成的目标数据类型：

|             | **INT32**                                                    | **INT64**                                                    | **FLOAT**                                       | **DOUBLE**              | **BOOLEAN**                                                  | **TEXT**                         |
| ----------- | ------------------------------------------------------------ | ------------------------------------------------------------ | ----------------------------------------------- | ----------------------- | ------------------------------------------------------------ | -------------------------------- |
| **INT32**   | 不转化                                                       | 直接转化                                                     | 直接转化                                        | 直接转化                | !=0 : true<br />==0: false                                   | String.valueOf()                 |
| **INT64**   | 超出 INT32 范围：执行抛异常<br />否则：直接转化              | 不转化                                                       | 直接转化                                        | 直接转化                | !=0L : true<br />==0: false                                  | String.valueOf()                 |
| **FLOAT**   | 超出 INT32 范围：执行抛异常<br />否则：四舍五入(Math.round()) | 超出 INT64 范围：执行抛异常<br />否则：四舍五入(Math.round()) | 不转化                                          | 直接转化                | !=0.0f : true<br />==0: false                                | String.valueOf()                 |
| **DOUBLE**  | 超出 INT32 范围：执行抛异常<br />否则：四舍五入(Math.round()) | 超出 INT64 范围：执行抛异常<br />否则：四舍五入(Math.round()) | 超出 FLOAT 范围：执行抛异常<br />否则：直接转化 | 不转化                  | !=0.0 : true<br />==0: false                                 | String.valueOf()                 |
| **BOOLEAN** | true: 1<br />false: 0                                        | true: 1L<br />false: 0                                       | true: 1.0f<br />false: 0                        | true: 1.0<br />false: 0 | 不转化                                                       | true: "true"<br />false: "false" |
| **TEXT**    | Integer.parseInt()                                           | Long.parseLong()                                             | Float.parseFloat()                              | Double.parseDouble()    | text.toLowerCase =="true" : true<br />text.toLowerCase =="false" : false<br />其它情况：执行抛异常 | 不转化                           |

#### 使用示例

```
// timeseries
IoTDB> show timeseries root.sg.d1.**
+-------------+-----+--------+--------+--------+-----------+----+----------+--------+------------------+
|   Timeseries|Alias|Database|DataType|Encoding|Compression|Tags|Attributes|Deadband|DeadbandParameters|
+-------------+-----+--------+--------+--------+-----------+----+----------+--------+------------------+
|root.sg.d1.s3| null| root.sg|   FLOAT|   PLAIN|     SNAPPY|null|      null|    null|              null|
|root.sg.d1.s4| null| root.sg|  DOUBLE|   PLAIN|     SNAPPY|null|      null|    null|              null|
|root.sg.d1.s5| null| root.sg| BOOLEAN|   PLAIN|     SNAPPY|null|      null|    null|              null|
|root.sg.d1.s6| null| root.sg|    TEXT|   PLAIN|     SNAPPY|null|      null|    null|              null|
|root.sg.d1.s1| null| root.sg|   INT32|   PLAIN|     SNAPPY|null|      null|    null|              null|
|root.sg.d1.s2| null| root.sg|   INT64|   PLAIN|     SNAPPY|null|      null|    null|              null|
+-------------+-----+--------+--------+--------+-----------+----+----------+--------+------------------+

// data of timeseries
IoTDB> select * from root.sg.d1;
+-----------------------------+-------------+-------------+-------------+-------------+-------------+-------------+
|                         Time|root.sg.d1.s3|root.sg.d1.s4|root.sg.d1.s5|root.sg.d1.s6|root.sg.d1.s1|root.sg.d1.s2|
+-----------------------------+-------------+-------------+-------------+-------------+-------------+-------------+
|1970-01-01T08:00:00.000+08:00|          0.0|          0.0|        false|        10000|            0|            0|
|1970-01-01T08:00:00.001+08:00|          1.0|          1.0|        false|            3|            1|            1|
|1970-01-01T08:00:00.002+08:00|          2.7|          2.7|         true|         TRue|            2|            2|
|1970-01-01T08:00:00.003+08:00|         3.33|         3.33|         true|        faLse|            3|            3|
+-----------------------------+-------------+-------------+-------------+-------------+-------------+-------------+

// cast BOOLEAN to other types
IoTDB> select cast(s5 as INT32), cast(s5 as INT64),cast(s5 as FLOAT),cast(s5 as DOUBLE), cast(s5 as TEXT) from root.sg.d1
+-----------------------------+----------------------------+----------------------------+----------------------------+-----------------------------+---------------------------+
|                         Time|CAST(root.sg.d1.s5 AS INT32)|CAST(root.sg.d1.s5 AS INT64)|CAST(root.sg.d1.s5 AS FLOAT)|CAST(root.sg.d1.s5 AS DOUBLE)|CAST(root.sg.d1.s5 AS TEXT)|
+-----------------------------+----------------------------+----------------------------+----------------------------+-----------------------------+---------------------------+
|1970-01-01T08:00:00.000+08:00|                           0|                           0|                         0.0|                          0.0|                      false|
|1970-01-01T08:00:00.001+08:00|                           0|                           0|                         0.0|                          0.0|                      false|
|1970-01-01T08:00:00.002+08:00|                           1|                           1|                         1.0|                          1.0|                       true|
|1970-01-01T08:00:00.003+08:00|                           1|                           1|                         1.0|                          1.0|                       true|
+-----------------------------+----------------------------+----------------------------+----------------------------+-----------------------------+---------------------------+

// cast TEXT to numeric types
IoTDB> select cast(s6 as INT32), cast(s6 as INT64), cast(s6 as FLOAT), cast(s6 as DOUBLE) from root.sg.d1 where time < 2
+-----------------------------+----------------------------+----------------------------+----------------------------+-----------------------------+
|                         Time|CAST(root.sg.d1.s6 AS INT32)|CAST(root.sg.d1.s6 AS INT64)|CAST(root.sg.d1.s6 AS FLOAT)|CAST(root.sg.d1.s6 AS DOUBLE)|
+-----------------------------+----------------------------+----------------------------+----------------------------+-----------------------------+
|1970-01-01T08:00:00.000+08:00|                       10000|                       10000|                     10000.0|                      10000.0|
|1970-01-01T08:00:00.001+08:00|                           3|                           3|                         3.0|                          3.0|
+-----------------------------+----------------------------+----------------------------+----------------------------+-----------------------------+

// cast TEXT to BOOLEAN
IoTDB> select cast(s6 as BOOLEAN) from root.sg.d1 where time >= 2
+-----------------------------+------------------------------+
|                         Time|CAST(root.sg.d1.s6 AS BOOLEAN)|
+-----------------------------+------------------------------+
|1970-01-01T08:00:00.002+08:00|                          true|
|1970-01-01T08:00:00.003+08:00|                         false|
+-----------------------------+------------------------------+
```