我在选择中有一个别名,如下所示:
SELECT
CASE ....
WHEN 1 THEN somefield * -10
WHEN 0 THEN somefield * 10
END as myAlias
FROM
....
问题是,在mysql查找的第一条记录中,它将“myAlias”标记为UNSIGNED
但在下一条记录中,同一个别名生成一个有符号整数,然后出现错误:
BIGINT UNSIGNED value is out of range in....
那么,在mysql执行任何操作之前,如何告诉它“myAlias”是有符号整数呢?
谢谢!
编辑:
我试过了
SELECT
CAST(CASE ....
WHEN 1 THEN somefield * -10
WHEN 0 THEN somefield * 10
END AS SIGNED) as myAlias
FROM
....
没有成功!
最佳答案
我假设表中的字段声明为UNSIGNED INTEGER
。在这种情况下,必须在THEN
表达式的CASE
子句中键入cast。下面的示例演示了一个示例。
创建并插入脚本:
CREATE TABLE mytable
(
numberfield INTEGER UNSIGNED
, bitfield BIT
);
INSERT INTO mytable (numberfield, bitfield) VALUES
(134, 1),
(673, 0),
(855, 1),
(133, 0),
(778, 1),
(234, 0);
在THEN子句中键入强制转换字段:SQL Fiddle Demo
SELECT
CASE bitfield
WHEN 1 THEN CAST(numberfield AS SIGNED) * -10
WHEN 0 THEN CAST(numberfield AS SIGNED) * 10
END as myAlias
FROM mytable
输出:
MYALIAS
-------
-1340
6730
-8550
1330
-7780
2340
编写上述查询的替代方法:SQL Fiddle Demo
SELECT
CAST(numberfield AS SIGNED) *
(
CASE bitfield
WHEN 1 THEN -10
WHEN 0 THEN 10
END
) as myAlias
FROM mytable
输出:
MYALIAS
-------
-1340
6730
-8550
1330
-7780
2340
不使用类型转换字段:SQL Fiddle Demo
SELECT
CASE bitfield
WHEN 1 THEN numberfield * -10
WHEN 0 THEN numberfield * 10
END as myAlias
FROM mytable
错误:
数据截断:BIGINT UNSIGNED value在“(
db_5b3bb
mytable
numberfield
*—(10))中超出范围:选择CASE bitfield WHEN 1,然后选择numberfield*-10 WHEN 0,然后选择numberfield*10 END作为myAlias FROM mytable