MySQL中经常使用的拼接语句的小结（代码示例）【MySQL教程】,mysql

本篇文章给人人带来的内容是关于MySQL中经常运用的拼接语句的小结（代码示例），有肯定的参考价值，有须要的朋侪能够参考一下，愿望对你有所协助。

媒介：在MySQL中 CONCAT ()函数用于将多个字符串衔接成一个字符串，应用此函数我们能够将本来一步没法获得的sql拼接出来，在工作中或许会轻易许多，下面重要引见下几个经常运用的场景。

注：适用于5.7版本 低版本能够稍许差别。

1.拼接查询一切用户

SELECT DISTINCT
    CONCAT(
        'User: \'',
        USER,
        '\'@\'',
        HOST,
        '\';'
    ) AS QUERY
FROM
    mysql.USER;
# 当拼接字符串中涌现'时 需运用\转义符

2.拼接DROP table

SELECT
    CONCAT(
        'DROP table ',
        TABLE_NAME,
        ';'
    )
FROM
    information_schema. TABLES
WHERE
    TABLE_SCHEMA = 'test';

3.拼接kill衔接

SELECT
    concat('KILL ', id, ';')
FROM
    information_schema. PROCESSLIST
WHERE
    STATE LIKE 'Creating sort index';

4.拼接建立数据库语句

SELECT
    CONCAT(
        'create database ',
        '`',
    SCHEMA_NAME,
    '`',
    ' DEFAULT CHARACTER SET ',
    DEFAULT_CHARACTER_SET_NAME,
        ';'
    ) AS CreateDatabaseQuery
FROM
    information_schema.SCHEMATA
WHERE
    SCHEMA_NAME NOT IN (
        'information_schema',
        'performance_schema',
        'mysql',
        'sys'
    );

5.拼接建立用户的语句

SELECT
    CONCAT(
        'create user \'',
    user,
    '\'@\'',
    Host,
    '\''
    ' IDENTIFIED BY PASSWORD \'',
    authentication_string,
        '\';'
    ) AS CreateUserQuery
FROM
    mysql.`user`
WHERE
    `User` NOT IN (
        'root',
        'mysql.session',
        'mysql.sys'
    );
#有暗码字符串哦 在其他实例实行 可直接建立出与本实例雷同暗码的用户

6.导出权限剧本 这个shell剧本也用到了拼接

#!/bin/bash  
#Function export user privileges  

pwd=yourpass  
expgrants()  
{  
  mysql -B -u'root' -p${pwd} -N $@ -e "SELECT CONCAT(  'SHOW GRANTS FOR ''', user, '''@''', host, ''';' ) AS query FROM mysql.user" | \
  mysql -u'root' -p${pwd} $@ | \
  sed 's/\(GRANT .*\)/\1;/;s/^\(Grants for .*\)/-- \1 /;/--/{x;p;x;}'  
}  
 
expgrants > /tmp/grants.sql
echo "flush privileges;" >> /tmp/grants.sql

7.查找表碎片

SELECT t.TABLE_SCHEMA,
       t.TABLE_NAME,
       t.TABLE_ROWS,
       concat(round(t.DATA_LENGTH / 1024 / 1024, 2), 'M') AS size,
       t.INDEX_LENGTH,
       concat(round(t.DATA_FREE / 1024 / 1024, 2), 'M') AS datafree
FROM information_schema.tables t
WHERE t.TABLE_SCHEMA = 'test' order by DATA_LENGTH desc;

8.查找无主键表 这个没用到拼接 也分享出来吧

#查找某一个库无主键表
SELECT
table_schema,
table_name
FROM
    information_schema.TABLES
WHERE
    table_schema = 'test'
AND TABLE_NAME NOT IN (
    SELECT
        table_name
    FROM
        information_schema.table_constraints t
    JOIN information_schema.key_column_usage k USING (
        constraint_name,
        table_schema,
        table_name
    )
    WHERE
        t.constraint_type = 'PRIMARY KEY'
    AND t.table_schema = 'test'
);

#查找除体系库外 无主键表
SELECT
    t1.table_schema,
    t1.table_name
FROM
    information_schema. TABLES t1
LEFT OUTER JOIN information_schema.TABLE_CONSTRAINTS t2 ON t1.table_schema = t2.TABLE_SCHEMA
AND t1.table_name = t2.TABLE_NAME
AND t2.CONSTRAINT_NAME IN ('PRIMARY')
WHERE
    t2.table_name IS NULL
AND t1.TABLE_SCHEMA NOT IN (
    'information_schema',
    'performance_schema',
    'mysql',
    'sys'
) ;

以上就是MySQL中经常运用的拼接语句的小结（代码示例）的细致内容，更多请关注ki4网别的相干文章！