Question

是否有一种功能可以更快速地检查Microsoft SQL Server Management Studio中给定值是否唯一？不包括以下内容：

DECLARE @username VARCHAR(45)
SET @username = 'foo'

DECLARE @checkTable INT

-- finds how many rows contain 'foo'
SET @checkTable = (SELECT COUNT(1) 
                   FROM table1 AS t
                   WHERE t.username = @username)
IF @checkTable = 0
-- Unique!

如果你有一张大桌子，这似乎很贵。我需要允许用户更改他/她现有的用户名，同时保持唯一。

由于

Answer 1

这可以节省几个字符......

DECLARE @username VARCHAR(45)
SET @username = 'foo'

IF NOT EXISTS(SELECT 1 FROM table1 WHERE username = @username)
BEGIN
    -- Unique!
END

Answer 2

IF EXISTS (SELECT 1 FROM table1 WHERE username = @Username)
BEGIN
     RETURN 'exists'
END
ELSE
BEGIN
     RETURN 'not exists'
END;

检查t-sql中值是否唯一的最佳方法

2 个答案: