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doris/docs/documentation/cn/sql-reference/sql-functions/cast.md
xy720 4c2a3d6da4 Merge Help document to documentation (#1586)
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2019-08-07 21:31:53 +08:00

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# CAST
## description
### Syntax
```
cast (input as type)
```
### BIGINT type
### Syntax(BIGINT)
``` cast (input as BIGINT) ```
将 input 转成 指定的 type
将当前列 input 转换为 BIGINT 类型
## example
1. 转常量,或表中某列
```
mysql> select cast (1 as BIGINT);
+-------------------+
| CAST(1 AS BIGINT) |
+-------------------+
| 1 |
+-------------------+
```
2. 转导入的原始数据
```
curl --location-trusted -u root: -T ~/user_data/bigint -H "columns: tmp_k1, k1=cast(tmp_k1 as BIGINT)" http://host:port/api/test/bigint/_stream_load
```
*注:在导入中,由于原始类型均为String,将值为浮点的原始数据做 cast的时候数据会被转换成 NULL ,比如 12.0 。Doris目前不会对原始数据做截断。*
如果想强制将这种类型的原始数据 cast to int 的话。请看下面写法:
```
curl --location-trusted -u root: -T ~/user_data/bigint -H "columns: tmp_k1, k1=cast(cast(tmp_k1 as DOUBLE) as BIGINT)" http://host:port/api/test/bigint/_stream_load
mysql> select cast(cast ("11.2" as double) as bigint);
+----------------------------------------+
| CAST(CAST('11.2' AS DOUBLE) AS BIGINT) |
+----------------------------------------+
| 11 |
+----------------------------------------+
1 row in set (0.00 sec)
```
##keyword
CAST