mysql 索引怎么实现（Mysql中索引和约束的示例语句）

mysql 索引怎么实现

Mysql中索引和约束的示例语句

外键

查询一个表的主键是哪些表的外键

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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

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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

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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

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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

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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

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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

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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

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1	ALTER TABLE `t_director` DROP FOREIGN KEY `fk_directorpid`;

修改值

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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

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1	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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原文链接：https://www.psvmc.cn/article/2020-12-23-mysql-constraint.html