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具体的upgrade脚本如下：
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动态删除索引
DROP PROCEDURE IF EXISTS UPGRADE;
DELIMITER $$
CREATE PROCEDURE UPGRADE()
BEGIN
-- RESOURCE.AUDIO_ATTRIBUTE
IF EXISTS(SELECT * FROM INFORMATION_SCHEMA.STATISTICS WHERE TABLE_SCHEMA = 'RESOURCE' AND TABLE_NAME = 'AUDIO_ATTRIBUTE' AND INDEX_NAME = 'resource_publish_resource_id_index')
THEN
ALTER TABLE `AUDIO_ATTRIBUTE` DROP INDEX resource_publish_resource_id_index;
END IF;
END$$
DELIMITER ;
CALL UPGRADE();
DROP PROCEDURE IF EXISTS UPGRADE;
动态添加字段
DROP PROCEDURE IF EXISTS UPGRADE;
DELIMITER $$
CREATE PROCEDURE UPGRADE()
BEGIN
-- HOMEWORK.HOMEWORK_QUESTION_GROUP.FROM_ID
IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = 'HOMEWORK' AND TABLE_NAME = 'HOMEWORK_QUESTION_GROUP' AND COLUMN_NAME = 'FROM_ID')
THEN
ALTER TABLE `HOMEWORK_QUESTION_GROUP` ADD COLUMN FROM_ID VARCHAR(50) NULL;
END IF;
-- HOMEWORK.HOMEWORK_QUESTION_GROUP.QUESTION_TYPE
IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = 'HOMEWORK' AND TABLE_NAME = 'HOMEWORK_QUESTION_GROUP' AND COLUMN_NAME = 'QUESTION_TYPE')
THEN
ALTER TABLE `HOMEWORK_QUESTION_GROUP` ADD COLUMN QUESTION_TYPE VARCHAR(50) NULL;
END IF;
-- HOMEWORK.HOMEWORK_QUESTION_GROUP.DIFFICULTY
IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = 'HOMEWORK' AND TABLE_NAME = 'HOMEWORK_QUESTION_GROUP' AND COLUMN_NAME = 'DIFFICULTY')
THEN
ALTER TABLE `HOMEWORK_QUESTION_GROUP` ADD COLUMN DIFFICULTY VARCHAR(50) NULL;
END IF;
END$$
DELIMITER ;
CALL UPGRADE();
DROP PROCEDURE IF EXISTS UPGRADE;
其他语法类似，主要区分EXISTS和 NOT EXISTS的用法。
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