Question

我有以下IF块，只有当我的表为空时才会执行该块。但它似乎是在BEGIN和END之间执行代码，即使我的表有一行。

IF ((SELECT COUNT(*) FROM [dbo].[KeyProperties]) = 0)
BEGIN
    INSERT INTO [dbo].[KeyProperties] (KeyId,PropertyId) VALUES
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=1),(SELECT Id FROM [dbo].[Properties] WHERE Name='SocialSecurityNumber'))
    INSERT INTO [dbo].[KeyProperties] (KeyId,PropertyId) VALUES
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=2),(SELECT Id FROM [dbo].[Properties] WHERE Name='FirstName')),
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=2),(SELECT Id FROM [dbo].[Properties] WHERE Name='LastName')),
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=2),(SELECT Id FROM [dbo].[Properties] WHERE Name='Email'))
END

上面的代码抛出了这个错误：

无法将值NULL插入列＆＃39; KeyId＆＃39;，表中＆＃39; MYDATABASE.dbo.KeyProperties＆＃39 ;;列不允许空值。插入失败。该语句已终止。端

Answer 1

1）使用NOT EXISTS而不是计数和比较0

2）使用INSERT INTO tab(col) SELECT

IF NOT EXISTS (SELECT 1 FROM [dbo].[KeyProperties])
BEGIN
    INSERT INTO [dbo].[KeyProperties] (KeyId,PropertyId)
    SELECT
      (SELECT Id FROM [dbo].[Keys] WHERE Priority=1),
      (SELECT Id FROM [dbo].[Properties] WHERE Name='SocialSecurityNumber');

   INSERT INTO [dbo].[KeyProperties] (KeyId,PropertyId)
   SELECT
      (SELECT Id FROM [dbo].[Keys] WHERE Priority=2),
      (SELECT Id FROM [dbo].[Properties] WHERE Name='FirstName')
   UNION ALL
   SELECT
      (SELECT Id FROM [dbo].[Keys] WHERE Priority=2),
      (SELECT Id FROM [dbo].[Properties] WHERE Name='LastName'),
   UNION ALL
   SELECT
      (SELECT Id FROM [dbo].[Keys] WHERE Priority=2),
      (SELECT Id FROM [dbo].[Properties] WHERE Name='Email');
END

Answer 2

改为使用变量：

DECLARE @Count INT
(SELECT @Count = COUNT(*) FROM [dbo].[KeyProperties])
IF (@Count = 0)

或只是

IF NOT EXISTS (SELECT TOP 1 NULL FROM [dbo].[KeyProperties])

Answer 3

尝试不存在于下面

IF Not Exists(SELECT 1 FROM [dbo].[KeyProperties])
BEGIN
    INSERT INTO [dbo].[KeyProperties] (KeyId,PropertyId) VALUES
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=1),(SELECT Id FROM [dbo].[Properties] WHERE Name='SocialSecurityNumber'))
    INSERT INTO [dbo].[KeyProperties] (KeyId,PropertyId) VALUES
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=2),(SELECT Id FROM [dbo].[Properties] WHERE Name='FirstName')),
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=2),(SELECT Id FROM [dbo].[Properties] WHERE Name='LastName')),
    ((SELECT Id FROM [dbo].[Keys] WHERE Priority=2),(SELECT Id FROM [dbo].[Properties] WHERE Name='Email'))
END

当条件不适用时执行IF块

3 个答案: