# 类型转换函数
#### 语法格式
```
CAST(value AS type)
```
#### 语法说明
类型强制转换。
#### 注意事项
若输入为NULL，则返回NULL。
#### 示例
将amount值转换成整型。
```
insert into temp select cast(amount as INT) from source_stream;
```
表1类型转换函数示例 
| 示例                    | 说明                                         | 示例                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|:---|:---|:---|
| cast(v1 as string)    | 将v1转换为字符串类型，v1可以是数值类型，TIMESTAMP/DATE/TIME。 | 表T1: ``` | content (INT)           | | -------------           | | 5                       | ``` 语句： ``` SELECT cast(content as varchar) FROM T1; ``` 结果： ``` "5" ```                            |
| cast (v1 as int)      | 将v1转换为int, v1可以是数值类型或字符类。                  | 表T1: ``` | content  (STRING)           | | -------------               | | "5"                         | ``` 语句： ``` SELECT cast(content as int) FROM T1; ``` 结果： ``` 5 ```                           |
| cast(v1 as timestamp) | 将v1转换为timestamp类型，v1可以是字符串或DATE/TIME。      | 表T1: ``` | content  (STRING)          | | -------------              | | "2018-01-01 00:00:01"     | ``` 语句： ``` SELECT cast(content as timestamp) FROM T1; ``` 结果： ``` 1514736001000 ``` |
| cast(v1 as date)      | 将v1转换为date类型， v1可以是字符串或者TIMESTAMP。         | 表T1: ``` | content  (TIMESTAMP)     | | -------------            | | 1514736001000            | ``` 语句： ``` SELECT cast(content as date) FROM T1; ``` 结果： ``` "2018-01-01" ```                   |
   
![](https://support.huaweicloud.com/sqlref-flink-dli/public_sys-resources/note_3.0-zh-cn.png)
Flink作业不支持使用CAST将"BIGINT"转换为"TIMESTAMP"，可以使用to_timestamp进行转换。
#### 详细样例代码
```
/** source **/
CREATE
TABLE car_infos (cast_int_to_string int, cast_String_to_int string,
case_string_to_timestamp string, case_timestamp_to_date timestamp(3)) WITH (
  'connector.type' = 'dis',
  'connector.region' = 'xxxxx',
  'connector.channel' = 'dis-input',
  'format.type' = 'json'
);
/** sink **/
CREATE
TABLE cars_infos_out (cast_int_to_string string, cast_String_to_int
int, case_string_to_timestamp timestamp(3), case_timestamp_to_date date) WITH (
  'connector.type' = 'dis',
  'connector.region' = 'xxxxx',
  'connector.channel' = 'dis-output',
  'format.type' = 'json'
);
/** 统计car的静态信息 **/
INSERT
INTO
  cars_infos_out
SELECT
  cast(cast_int_to_string as string),
  cast(cast_String_to_int as int),
  cast(case_string_to_timestamp as timestamp),
  cast(case_timestamp_to_date as date)
FROM
  car_infos;
```