SQL 服务器 : Is there a way to check what is the resulting data type of implicit conversion?

Question

有没有办法检查隐式转换的结果数据类型是什么？还是只需要根据加入算术运算的数据类型就知道了？

declare @i as int
set @i = 3
select @i  / 9.0 as returning_numeric

Answer 1

表达式的结果是numeric (17,6)。看到这个

DECLARE @i  INT, @v SQL_VARIANT

SET @i = 3
SET @v = @i  / 9.0

SELECT
    CAST(SQL_VARIANT_PROPERTY(@v, 'BaseType') AS VARCHAR(30)) AS BaseType,
    CAST(SQL_VARIANT_PROPERTY(@v, 'Precision') AS INT) AS Precision,
    CAST(SQL_VARIANT_PROPERTY(@v, 'Scale') AS INT) AS Scale

返回

BaseType   Precision   Scale
---------- ----------- -----------
numeric    17          6

编辑:

SELECT SQL_VARIANT_PROPERTY(9.0, 'BaseType'),
       SQL_VARIANT_PROPERTY(9.0, 'Precision'),
       SQL_VARIANT_PROPERTY(9.0, 'Scale')

所以文字9.0被当作numeric(2,1)(从上面的查询可以看出)

@i 是 numeric(10,0)(根据 Mikael's answer )

控制为什么 numeric(10,0)/numeric(2,1) 给出 numeric (17,6) 的规则 are covered here

Operation:        e1 / e2
Result precision: p1 - s1 + s2 + max(6, s1 + p2 + 1)
Result scale:     max(6, s1 + p2 + 1)

将相关值代入给定

10 - 0 + 1 + max(6, 0 + 2 + 1)  = 17
max(6, 0 + 2 + 1)               =  6