问题描述
有没有办法在 ALTER TABLE ADD coumn_name
语句运行之前(或运行时)检查 mySQL 数据库中是否存在列?类似于 IF 列不存在 ALTER TABLE
的东西.
Is there a way to check if a column exists in a mySQL DB prior to (or as) the ALTER TABLE ADD coumn_name
statement runs? Sort of an IF column DOES NOT EXIST ALTER TABLE
thing.
我已经尝试了 ALTER IGNORE TABLE my_table ADD my_column
但如果我添加的列已经存在,这仍然会引发错误.
I've tried ALTER IGNORE TABLE my_table ADD my_column
but this still throws the error if the column I'm adding already exists.
用例是升级已安装的网络应用程序中的表 - 为了简单起见,我想确保我需要的列存在,如果不存在,请使用 添加它们更改表
use case is to upgrade a table in an already installed web app-- so to keep things simple, I want to make sure the columns I need exist, and if they don't, add them using ALTER TABLE
推荐答案
由于 mysql 控制语句(例如IF")只在存储过程中起作用,因此可以创建并执行临时的:
Since mysql control statements (e.g. "IF") only work in stored procedures, a temporary one can be created and executed:
DROP PROCEDURE IF EXISTS add_version_to_actor;
DELIMITER $$
CREATE DEFINER=CURRENT_USER PROCEDURE add_version_to_actor ( )
BEGIN
DECLARE colName TEXT;
SELECT column_name INTO colName
FROM information_schema.columns
WHERE table_schema = 'connjur'
AND table_name = 'actor'
AND column_name = 'version';
IF colName is null THEN
ALTER TABLE actor ADD version TINYINT NOT NULL DEFAULT '1' COMMENT 'code version of actor when stored';
END IF;
END$$
DELIMITER ;
CALL add_version_to_actor;
DROP PROCEDURE add_version_to_actor;
这篇关于在 ALTER TABLE -- mysql 之前检查列是否存在的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!