Mysql中索引和约束的示例语句

时间:2021-01-03 码客人气:1

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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