sql - 在 SQL 中减去变量

Question

如何减去两个变量的值。这是我到目前为止所做的

DECLARE @A NVARCHAR(MAX)
DECLARE @B NVARCHAR(MAX)

SET @A='select count(abc)
 from x'
 EXEC (@A)
 PRINT @A

 SET @B= ' select count(xyz)
 from  y'

 EXEC (@B)
 PRINT @B

 DECLARE @C INT
 SET @C = CAST(@A AS INT) - CAST(@B AS INT)
 EXEC (@C)
 PRINT @C

我收到转换错误

Msg 245, Level 16, State 1, Line 20
Conversion failed when converting the nvarchar value

Answer 1

当然你会得到一个转换错误，因为变量是一个字符串。即使该字符串是一个查询，如果您执行它，您也不会将结果存储回您的变量。您需要做的是:

DECLARE @A INT, @B INT, @C INT;

SELECT @A = COUNT(abc)
FROM x;

SELECT @B = COUNT(xyz)
FROM y;

SET @C = @A - @B;