动态更改表中的Mysql调用过程失败 [英] Mysql calling procedure failed when dynamically alter table in it

问题描述

我想根据表是否具有特定的列来动态更改表.

I want to alter my tables dynamically based on whether the table has specific column.

我的数据库名称是summer_cms，其中有50多个表.

My database name is summer_cms, and there are over 50 tables in it.

我想要的东西如下:

1. 如果表中有名为add_time的列，那么我想在其中添加列add_user_id.
2. 类似地，如果找到了update_time，我想在表中添加update_user_id.

1. If a table has a column named add_time, then I would like to add a column add_user_id in it.
2. Similarly, I would like to add update_user_id in the table if update_time is found.

我知道在创建数据库模式的过程中应该把它记下来，但是我的数据库已经构建好了，我必须根据需要对其进行更改.

I know I should get it down in the process of creating the database schemas, but my database has been built and I have to alter it by need.

所以我创建了一个程序来做:

So I create a procedure to do it:

CREATE PROCEDURE ALTER_SUMMER_TABLE()
BEGIN
    DECLARE tableName VARCHAR(64);
    DECLARE exitence VARCHAR(64);

    DECLARE ntable INT;    # number of tables
    DECLARE i INT;         # index
    SET i = 0;

    # get the count of table
    SELECT COUNT(DISTINCT(TABLE_NAME)) INTO ntable FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = 'summer_cms';

    WHILE i < ntable DO
        # select the specific table name into the variable of `tableName`.
        SELECT TABLE_NAME INTO tableName
        FROM information_schema.COLUMNS
        WHERE TABLE_SCHEMA = 'summer_cms'
        AND COLUMN_NAME = 'add_time'
        LIMIT 1 OFFSET i;

        # alter table, but I get error in this clause.
        ALTER TABLE tableName ADD COLUMN `add_user_id` INT NOT NULL DEFAULT 0 COMMENT 'add user id';

        # check if the table has `update_time`
        SELECT TABLE_NAME INTO exitence
        FROM information_schema.COLUMNS
        WHERE TABLE_SCHEMA = 'summer_cms'
        AND TABLE_NAME = tableName
        AND COLUMN_NAME = 'update_time';

        # add `update_user_id` if `update_time` be found.
        IF exitence THEN
            ALTER TABLE tableName ADD COLUMN `update_user_id` INT NOT NULL DEFAULT 0 COMMENT 'update user id';
        END IF;
        SET i = i + 1;
    END WHILE;
END

但是调用此过程时出现错误.

But I got an error when I call this procedure.

Procedure execution failed
1146 - Table 'summer_cms.tableName' doesn't exist

有人能告诉我我想念什么或做错了什么吗?任何帮助将不胜感激.

Dose anyone could tell me what I was missing or wrong? Any help will be appreciated.

推荐答案

您可以对过程进行一些更改，以使其更加简化并解决一些问题.

There a a few alterations you can make to your procedure to make it more streamlined as well as getting round a few problems.

首先使用光标选择表名，而不是使用两个选择您要使用的表名.其次使用准备好的语句来允许您动态设置表名...

First using a cursor to select the table names rather than using the two selects your using. Secondly to use a prepared statement to allow you to dynamically set the table name...

DELIMITER $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `ALTER_SUMMER_TABLE`()
BEGIN
    DECLARE done INT DEFAULT 0;
    DECLARE tableName VARCHAR(64);
    declare cur cursor for SELECT TABLE_NAME
                             FROM information_schema.COLUMNS
                            WHERE TABLE_SCHEMA = 'summer_cms'
                            AND COLUMN_NAME = 'add_time';
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

    open cur;

    start_loop: loop
        fetch cur into tableName;
        if (done = 1 )THEN
             LEAVE start_loop;
        END IF;
        SET @sql = CONCAT('ALTER TABLE ', tableName,' ADD COLUMN `add_user_id` INT NOT NULL DEFAULT 0 ');
        PREPARE stmt FROM @sql;
        EXECUTE stmt;

    end loop;

    close cur;
END$$
DELIMITER ;

您可以做一些调整-例如仅获取不存在该列的表名.

You could do a few tweaks - only fetch table names where the column doesn't already exist for example.

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