Question

IF EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'X' AND COLUMN_NAME = 'Y') 

IF EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'Z' AND COLUMN_NAME = 'A')
BEGIN
    UPDATE [dbo].[X] 
        SET Y= (SELECT inst.[A] FROM [dbo].[Z] s WHERE s.[B] = [dbo].[x].[B]);
END    
    GO

我希望结合2个IF条件，并仅在满足两个条件时执行更新。我有什么方法可以参加2 IF EXISTS吗？

Answer 1

简单：

IF EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'X' AND COLUMN_NAME = 'Y') 
AND EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'Z' AND COLUMN_NAME = 'A')

BEGIN
    UPDATE [dbo].[X] 
        SET Y= (SELECT inst.[A] FROM [dbo].[Z] s WHERE s.[B] = [dbo].[x].[B]);
END    
GO

Answer 2

不需要通过SELECT *选择所有列。因为您正在检查是否存在行，所以请执行SELECT 1以更快地进行查询。

IF EXISTS(SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS
              WHERE TABLE_NAME = 'X' AND COLUMN_NAME = 'Y')

IF EXISTS(SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS 
          WHERE  TABLE_NAME = 'Z' AND COLUMN_NAME = 'A')

    BEGIN
        UPDATE [dbo].[X] 
            SET Y= (SELECT inst.[A] FROM [dbo].[Z] s WHERE s.[B] = [dbo].[x].[B]);
    END    
        GO

Answer 3

将标题和说明更改为空

UPDATE `li_categories`
  SET description = CASE
    WHEN description = '' THEN CONCAT('optional text ', title, ' optional text')
    ELSE description
    END
WHERE
 id

如何在SQL中的IF EXISTS中使用AND条件？

3 个答案: