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版本:3.0

CAST

功能

input 转换成指定数据类型的值,如 cast (input as BIGINT) 将当前 input 转换为 BIGINT 类型的值。

从 2.4 版本开始支持将 Array 字符串 和 JSON array 转换为 ARRAY 类型。

语法

cast(input as type)

参数说明

input: 待转换类型的数据

type: 目标数据类型

返回值说明

返回值的数据类型为 type 指定的类型。如果转化失败,返回 NULL。

示例

示例一:常见转换。

    select cast (1 as BIGINT);
+-------------------+
| CAST(1 AS BIGINT) |
+-------------------+
| 1 |
+-------------------+

select cast('9.5' as DECIMAL(10,2));
+--------------------------------+
| CAST('9.5' AS DECIMAL64(10,2)) |
+--------------------------------+
| 9.50 |
+--------------------------------+

select cast(NULL AS INT);
+-------------------+
| CAST(NULL AS INT) |
+-------------------+
| NULL |
+-------------------+

select cast(true AS BOOLEAN);
+-----------------------+
| CAST(TRUE AS BOOLEAN) |
+-----------------------+
| 1 |
+-----------------------+

示例二:转换为 ARRAY 类型。

    -- Convert string to ARRAY<ANY>.

select cast('[1,2,3]' as array<int>);
+-------------------------------+
| CAST('[1,2,3]' AS ARRAY<INT>) |
+-------------------------------+
| [1,2,3] |
+-------------------------------+

select cast('[1,2,3]' as array<bigint>);
+----------------------------------+
| CAST('[1,2,3]' AS ARRAY<BIGINT>) |
+----------------------------------+
| [1,2,3] |
+----------------------------------+

select cast('[1,2,3]' as array<string>);
+------------------------------------------+
| CAST('[1,2,3]' AS ARRAY<VARCHAR(65533)>) |
+------------------------------------------+
| ["1","2","3"] |
+------------------------------------------+

select cast('["a", "b", "c"]' as array<string>);
+--------------------------------------------------+
| CAST('["a", "b", "c"]' AS ARRAY<VARCHAR(65533)>) |
+--------------------------------------------------+
| ["a","b","c"] |
+--------------------------------------------------+

-- Convert JSON array to ARRAY<ANY>.

select cast(parse_json('[{"a":1}, {"a": 2}]') as array<json>);
+----------------------------------------------------------+
| CAST((parse_json('[{"a":1}, {"a": 2}]')) AS ARRAY<JSON>) |
+----------------------------------------------------------+
| ['{"a": 1}','{"a": 2}'] |
+----------------------------------------------------------+

select cast(parse_json('[1, 2, 3]') as array<int>);
+-----------------------------------------------+
| CAST((parse_json('[1, 2, 3]')) AS ARRAY<INT>) |
+-----------------------------------------------+
| [1,2,3] |
+-----------------------------------------------+

select cast(parse_json('["1","2","3"]') as array<string>);
+--------------------------------------------------------------+
| CAST((parse_json('["1","2","3"]')) AS ARRAY<VARCHAR(65533)>) |
+--------------------------------------------------------------+
| ["1","2","3"] |
+--------------------------------------------------------------+

示例三:导入中转换原始数据。

curl --location-trusted -u <username>:<password> -T ~/user_data/bigint \

-H "columns: tmp_k1, k1=cast(tmp_k1 as BIGINT)" \

http://host:port/api/test/bigint/_stream_load

说明

在导入过程中,对于原始数据类型为浮点数的 STRING 做转换时,数据会被转换成 NULL。比如浮点数 12.0 会转为 NULL。如果想强制将这种类型的原始数据转为 BIGINT,需要先将STRING类型的浮点数转为DOUBLE,再转为 BIGINT,请参考如下示例:

curl --location-trusted -u <username>:<password> -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
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)