Question

我有一个用于插入的存储过程。当我我正在插入一条记录，我希望发布的价值等于超过最高值的一个。所以在这里是我编码的：

    DECLARE @MaxRelease int;

    SELECT @MaxRelease = max(Release)
    FROM   dbo.Test
    WHERE  TestTypeId = @TestTypeId
    AND    ExamId     = @ExamId
    AND    Title      = @Title;

    INSERT ... @MaxRelease + 1 ... etc.

但是我怎么能这样做，以便如果SELECT没有返回任何内容（因为没有当前的记录）@MaxRelease的值是0？

Answer 1

您可以使用ISNULL (Transact-SQL)将空值替换为替换值。

SELECT @MaxRelease = isnull(max(Release), 0)
FROM   dbo.Test

Answer 2

将@MaxRelease指定为初始值零。

DECLARE @MaxRelease int = 0;

SELECT @MaxRelease = max(Release)
FROM   dbo.Test
WHERE  TestTypeId = @TestTypeId
AND    ExamId     = @ExamId
AND    Title      = @Title
GROUP BY TestTypeId;

如果select中没有返回任何内容，则不会修改@MaxRelease。

Answer 3

试试这个

DECLARE @MaxRelease int;

SELECT @MaxRelease = max(Release)
FROM   dbo.Test
WHERE  TestTypeId = @TestTypeId
AND    ExamId     = @ExamId
AND    Title      = @Title;

INSERT ... CASE WHEN @MaxRelease IS NULL THEN 0 ELSE @MaxRelease + 1 END ... etc.

Answer 4

尝试使用ISNULL或COALESCE

等

SELECT @MaxRelease = isnull(max(Release),0)
FROM   dbo.Test
WHERE  TestTypeId = @TestTypeId
AND    ExamId     = @ExamId
AND    Title      = @Title;

OR

if @MaxRelease is null
begin
set @MaxRelease =0
end

Then Execute Insert Query here.

如果我的SELECT中没有匹配记录，如何从记录中获取列的MAX值或0？

4 个答案: