Question

如果top clause参数为null，有没有办法选择记录？

DECLARE @count FLOAT = 0;

Select @count = count from tblDetails

SELECT TOP(@count) from tblCompany

如果@count var为null，则我想从tblCompany中选择所有记录。

Answer 1

DECLARE @count FLOAT = 0;

Select @count = count(1) from tblDetails

IF @count > 0
BEGIN
SELECT TOP(@intRecords) * from tblCompany
END
ELSE
BEGIN
SELECT * FROM tblCompany
END

如果你不想写两次查询 - 虽然只有一个会被执行，你可以试试这个：

    DECLARE @count FLOAT = 0;

    Select @count = count(1) from tblDetails

    IF @count = 0
    BEGIN
    SET @intRecords = 100000 -- Or some number larger than the possible count
    END
    SELECT TOP(@intRecords) * from tblCompany

Answer 2

当遇到像这样的情况时，我喜欢使用SQL Rank。

在下面的查询中，我假设您有一个ID列，但您可以将其替换为任何其他列，以选择最佳列的标准：

DECLARE @count FLOAT = 0;
Select @count = count(*) from tblDetails

SELECT * FROM 
(
    SELECT      
    RANK () OVER 
    ( ORDER BY ID ) 'Rank', -- <-- Assuming you have an ID column, replace with any other criteria for what will be considered as top...
    *
FROM tblCompany
) tmp
WHERE (@count IS NULL) OR tmp.Rank <= @count

Answer 3

我认为这样可行：

DECLARE @count AS INT ;

Set @count = (Select count(*) from tblDetails);

SELECT TOP(ISNULL(@count,5)) * from tblCompany

如果top clause参数为null，有没有办法选择记录？

3 个答案: