Question

如何减去两个变量中的值。这是我到目前为止所做的事情

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
转换nvarchar值时转换失败

Answer 1

当然，您会收到转换错误，因为该变量是一个字符串。即使字符串是查询，如果执行它，也不会将结果存储回变量。你需要做的是：

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

SELECT @A = COUNT(abc)
FROM x;

SELECT @B = COUNT(xyz)
FROM y;

SET @C = @A - @B;

Answer 2

在您的代码中，@A和@B将保存sql语句，而不是结果。如果你想运行一个dunamic sql语句并从中获取一些输出，你需要检查sp_executesql你可以在哪里定义输出参数。

您的代码的正确实现如下：

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

DECLARE @SQLString nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);

SET @SQLString = N'select  @test = count(abc) from x'
SET @ParmDefinition = N'@test int OUTPUT';

EXECUTE sp_executesql @SQLString, @ParmDefinition, @A=@test OUTPUT;

SET @SQLString = N'select  @test = count(xyz) from y'

EXECUTE sp_executesql @SQLString, @ParmDefinition, @B=@test OUTPUT;

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

另一个注意事项是，将@A和@B声明为(MAX)太多了...... 如果你将它们声明为INT并避免额外的演员表会更好：

DECLARE @A INT
DECLARE @B INT

DECLARE @SQLString nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);

SET @SQLString = N'select  @test = count(abc) from x'
SET @ParmDefinition = N'@test int OUTPUT';

EXECUTE sp_executesql @SQLString, @ParmDefinition, @A=@test OUTPUT;

SET @SQLString = N'select  @test = count(xyz) from y'

EXECUTE sp_executesql @SQLString, @ParmDefinition, @B=@test OUTPUT;

DECLARE @C INT
SET @C = @A - @B

Answer 3

测试数据：

IF OBJECT_ID(N'Table1')>0
BEGIN
    DROP TABLE Table1
END

IF OBJECT_ID(N'Table2')>0
BEGIN
    DROP TABLE Table2
END

CREATE TABLE Table1 (Col1 VARCHAR(100))
CREATE TABLE Table2 (Col2 VARCHAR(100))

INSERT INTO Table1
VALUES('1'),('2'),('3'),('4')

INSERT INTO Table2
VALUES('2'),('4')

查询：

DECLARE @A NVARCHAR(MAX)
DECLARE @B NVARCHAR(MAX)
DECLARE @C INT
DECLARE @ACount INT
DECLARE @BCount INT

SET @A='SELECT @ACount = COUNT(Col1) FROM Table1'
SET @B='SELECT @BCount = COUNT(Col2) FROM Table2'

exec sp_executesql @A, N'@ACount int out', @ACount out
exec sp_executesql @b, N'@BCount int out', @BCount out

SET @C = @ACount - @BCount

PRINT @C

<强>清理：

IF OBJECT_ID(N'Table1')>0
BEGIN
    DROP TABLE Table1
END

IF OBJECT_ID(N'Table2')>0
BEGIN
    DROP TABLE Table2
END

在SQL中减去变量

3 个答案: