遍历所有表并重命名列 [英] Loop through all tables and rename a column

问题描述

一个客户端给了我一个遗留数据库old_data，其中包含一堆表，我将在新系统中逐步激活这些表.不幸的是，有两个表包含一列名为hash的列，该列与我用来处理该项目的Ruby on Rails不太兼容.

A client gave me a legacy database old_data which contains a bunch of tables which I'm going to activate in a new system step by step. Unfortunately a couple of the tables contain a column with the name hash which doesn't float well with Ruby on Rails which I use to tackle this project.

是否有一种方法可以告诉MySQL控制台中的MySQL(版本8.0.12)遍历给定数据库中的所有表，并将列hash重命名为old_hash(如果该列存在)?

Is there a way to tell MySQL (version 8.0.12) in the MySQL console to loop through all tables in the given database and rename the column hash to old_hash if that column exists?

推荐答案

幸运的是，MySQL 8带有ALTER TABLE RENAME COLUMN a TO b语法，因此您可以编写一个相当简单的存储过程来做到这一点.

Luckily MySQL 8 comes with an ALTER TABLE RENAME COLUMN a TO b syntax so you can write a reasonably straightforward stored procedure to do this.

DELIMITER //

CREATE PROCEDURE rename_columns(IN name_of_database CHAR(64),
                                IN old_name_of_column CHAR(64),
                                IN new_name_of_column CHAR(64))
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE name_of_table CHAR(64);
    DECLARE table_cursor CURSOR FOR
        SELECT TABLE_NAME FROM information_schema.COLUMNS
        WHERE TABLE_SCHEMA = name_of_database AND COLUMN_NAME = old_name_of_column;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    OPEN table_cursor;
    table_loop: LOOP
        FETCH table_cursor INTO name_of_table;
        IF done THEN LEAVE table_loop; END IF;
        SET @alter_sql = CONCAT(
            'ALTER TABLE ', name_of_database, '.', name_of_table,
            ' RENAME COLUMN ', old_name_of_column, ' TO ', new_name_of_column);
        PREPARE alter_statement FROM @alter_sql;
        EXECUTE alter_statement;
        DEALLOCATE PREPARE alter_statement;
    END LOOP;
    CLOSE table_cursor;
END//

DELIMITER ;

CALL rename_columns('old_data', 'hash', 'old_hash');

在5.7及更早版本中，它更为复杂，因为您需要生成一个包含完整列定义的ALTER TABLE CHANGE a b ...语句.

It's more complicated in 5.7 and earlier because you'll need to generate an ALTER TABLE CHANGE a b ... statement which includes the full column definition.

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