MySQL添加列(如果不存在) [英] MySQL add column if not exist

问题描述

IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
  WHERE TABLE_NAME = 'email_subscription' AND COLUMN_NAME = 'subscribe_all')
  THEN 
  ALTER TABLE email_subscription
  ADD COLUMN subscribe_all TINYINT(1) DEFAULT 1,
  ADD COLUMN subscribe_category varchar(512) DEFAULT NULL;

我看了很多例子.但是此查询不起作用，出现以下错误:

I had a look at huge amount of examples. but this query doesn't work, I got error of:

错误1064(42000):您的SQL语法有错误；检查 与您的MySQL服务器版本相对应的手册 在'IF NOT EXISTS(SELECT * FROM 第1行的INFORMATION_SCHEMA.COLUMNS TABLE_NAME ='

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME =' at line 1

推荐答案

您可以为查询创建一个过程，

you can create a procedure for the query,

DELIMITER $$
CREATE PROCEDURE Alter_Table()
BEGIN
    DECLARE _count INT;
    SET _count = (  SELECT COUNT(*) 
                    FROM INFORMATION_SCHEMA.COLUMNS
                    WHERE   TABLE_NAME = 'email_subscription' AND 
                            COLUMN_NAME = 'subscribe_all');
    IF _count = 0 THEN
        ALTER TABLE email_subscription
            ADD COLUMN subscribe_all TINYINT(1) DEFAULT 1,
            ADD COLUMN subscribe_category varchar(512) DEFAULT NULL;
    END IF;
END $$
DELIMITER ;

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