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