Mysql中索引和约束的示例语句
编程学习 2021-07-05 14:37www.dzhlxh.cn编程入门
这篇文章主要介绍了Mysql中索引和约束的相关资料，帮助大家更好的理解和使用MySQL，感兴趣的朋友可以了解下
外键
查询一个表的主键是哪些表的外键
SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE TABLE_SCHEMA = 'mydbname' AND REFERENCED_TABLE_NAME = '表名';
导出所有外键语句
SELECT
CONCAT('ALTER TABLE ', TABLE_NAME, ' ADD CONSTRAINT ', CONSTRAINT_NAME, ' FOREIGN KEY (', COLUMN_NAME, ') REFERENCES ', REFERENCED_TABLE_NAME, '(', REFERENCED_COLUMN_NAME, ') ON DELETE CASCADE ON UPDATE CASCADE;')
FROM
INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE
TABLE_SCHEMA = 'mydbname'
AND REFERENCED_TABLE_NAME IS NOT NULL;
删除所有外键语句
SELECT
CONCAT('ALTER TABLE ', TABLE_NAME, ' DROP FOREIGN KEY ', CONSTRAINT_NAME, ';')
FROM
INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE
TABLE_SCHEMA = 'mydbname'
AND REFERENCED_TABLE_NAME IS NOT NULL;
自增
导出创建自增字段的语句
SELECT CONCAT( 'ALTER TABLE `', TABLE_NAME, '` ', 'MODIFY COLUMN `', COLUMN_NAME, '` ', UPPER( COLUMN_TYPE ), ' NOT NULL AUTO_INCREMENT COMMENT "',COLUMN_COMMENT,'";' ) as 'ADD_AUTO_INCREMENT' FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = 'mydbname' AND EXTRA = UPPER( 'AUTO_INCREMENT' ) ORDER BY TABLE_NAME ASC;
创建删除所有自增字段
SELECT CONCAT( 'ALTER TABLE `', TABLE_NAME, '` ', 'MODIFY COLUMN `', COLUMN_NAME, '` ', UPPER( COLUMN_TYPE ), ' NOT NULL;' ) as 'DELETE_AUTO_INCREMENT' FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = 'mydbname' AND EXTRA = UPPER( 'AUTO_INCREMENT' ) ORDER BY TABLE_NAME ASC;
索引
导出所有索引
SELECT CONCAT( 'ALTER TABLE `', TABLE_NAME, '` ', 'ADD ', IF ( NON_UNIQUE = 1, CASE UPPER( INDEX_TYPE ) WHEN 'FULLTEXT' THEN 'FULLTEXT INDEX' WHEN 'SPATIAL' THEN 'SPATIAL INDEX' ELSE CONCAT( 'INDEX `', INDEX_NAME, '` USING ', INDEX_TYPE ) END, IF ( UPPER( INDEX_NAME ) = 'PRIMARY', CONCAT( 'PRIMARY KEY USING ', INDEX_TYPE ), CONCAT( 'UNIQUE INDEX `', INDEX_NAME, '` USING ', INDEX_TYPE ))), CONCAT( '(`', COLUMN_NAME, '`)' ), ';' ) AS 'ADD_ALL_INDEX' FROM information_schema.STATISTICS WHERE TABLE_SCHEMA = 'mydbname' ORDER BY TABLE_NAME ASC, INDEX_NAME ASC;
删除所有索引
SELECT CONCAT( 'ALTER TABLE `', TABLE_NAME, '` ', CONCAT( 'DROP ', IF ( UPPER( INDEX_NAME ) = 'PRIMARY', 'PRIMARY KEY', CONCAT( 'INDEX `', INDEX_NAME, '`' ))), ';' ) AS 'DELETE_ALL_INDEX' FROM information_schema.STATISTICS WHERE TABLE_SCHEMA = 'mydbname' ORDER BY TABLE_NAME ASC;
数据合并
在数据迁移合并的时候，比较棘手的是不同数据库主键重复，那么我们就要批量修改主键的值，为了避免重复我们可以把自增的数字改为字符串
步骤基本上有以下几步
- 取消主键自增
- 删除所有外键
- 修改主键字段为varchar
- 添加所有外键
- 修改主键的值
- 合并数据
修改主键值的时候要注意
如果包含id和pid这种自关联的情况下是不能直接修改值的，就需要先删除约束再添加。
比如
删除自约束
ALTER TABLE `t_director` DROP FOREIGN KEY `fk_directorpid`;
修改值
update t_director set directorid=directorid+100000000; update t_director set directorid=CONV(directorid,10,36); update t_director set directorpid=directorpid+100000000 WHERE directorpid is not null; update t_director set directorpid=CONV(directorpid,10,36) WHERE directorpid is not null;
添加自约束
ALTER TABLE t_director ADD CONSTRAINT fk_directorpid FOREIGN KEY (directorpid) REFERENCES t_director(directorid) ON DELETE CASCADE ON UPDATE CASCADE;
注意
CONV(directorpid,10,36)后两个参数为原数字进制和要转换后的进制。
第一个参数只要内容是数字就算类型为varchar也可以转换。
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