使用多个别名列时将数据类型varchar转换为数字时出错

Question

我有一个表，该表具有5个定义的列（id，colA，colB，colC，colD），所有数据类型均为decimal(18, 3)，但id除外。

SELECT 
    [id],
    [colA], [colB], [colC], [colD],
    colA - colB as length,
    colC - colD * 2 as width,
    //colA + width - length as colMod0
    //modified the code
    (select
    colA + width - length
    from [dbo].[main]
    ) as colMod0
    //Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.



FROM 
    [dbo].[main]
ORDER BY
    _main.id;

执行此代码时出现错误

将数据类型varchar转换为数字时出错

我试图进行转换和转换，但没有成功。长度，宽度和colMod0均为别名列。

Answer 1

该错误消息与类型无关。相反，它只是告诉您别名不能在同一级别的select语句中重用。一种解决方案是只重复width和length的表达式：

SELECT [id], [colA], [colB], [colC], [colD],
    colA-colB AS length,
    colC-colD*2 AS width,
    colA + (colC-colD*2) - (colA-colB) AS colMod0
FROM [dbo].[main]
ORDER BY _main.id;