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Mysql中索引和約束的示例語(yǔ)句

 更新時(shí)間：2021年01月03日 09:51:21   作者：碼客  
這篇文章主要介紹了Mysql中索引和約束的相關(guān)資料，幫助大家更好的理解和使用MySQL，感興趣的朋友可以了解下

外鍵

查詢一個(gè)表的主鍵是哪些表的外鍵

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';

導(dǎo)出所有外鍵語(yǔ)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;

刪除所有外鍵語(yǔ)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

導(dǎo)出創(chuàng)建自增字段的語(yǔ)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;

創(chuàng)建刪除所有自增字段

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

導(dǎo)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;

刪除所有索引

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;

數(shù)據(jù)合并

在數(shù)據(jù)遷移合并的時(shí)候，比較棘手的是不同數(shù)據(jù)庫(kù)主鍵重復(fù)，那么我們就要批量修改主鍵的值，為了避免重復(fù)我們可以把自增的數(shù)字改為字符串

步驟基本上有以下幾步

  • 取消主鍵自增
  • 刪除所有外鍵
  • 修改主鍵字段為varchar
  • 添加所有外鍵
  • 修改主鍵的值
  • 合并數(shù)據(jù)

修改主鍵值的時(shí)候要注意

如果包含id和pid這種自關(guān)聯(lián)的情況下是不能直接修改值的，就需要先刪除約束再添加。

比如

刪除自約束

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;

添加自約束

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)后兩個(gè)參數(shù)為原數(shù)字進(jìn)制和要轉(zhuǎn)換后的進(jìn)制。

第一個(gè)參數(shù)只要內(nèi)容是數(shù)字就算類型為varchar也可以轉(zhuǎn)換。

以上就是Mysql中索引和約束的示例語(yǔ)句的詳細(xì)內(nèi)容，更多關(guān)于MySQL 索引和約束的資料請(qǐng)關(guān)注腳本之家其它相關(guān)文章！

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