mysql

查看所以库大小
select TABLE_SCHEMA, concat(truncate(sum(data_length)/1024/1024,2),' MB') as data_size,

concat(truncate(sum(index_length)/1024/1024,2),'MB') as index_size

from information_schema.tables

group by TABLE_SCHEMA

order by data_length desc;

查询 表结构
show create tables tablename
查询视图结构
show create view viem.name
查询数据库中的存储过程和函数

   select `name` from mysql.proc where db = 'xx' and `type` = 'PROCEDURE'   //存储过程
   select `name` from mysql.proc where db = 'xx' and `type` = 'FUNCTION'   //函数

   show procedure status; //存储过程
   show function status;     //函数

查看存储过程或函数的创建代码

　　show create procedure proc_name;
　　show create function func_name;

查看视图
　　SELECT from information_schema.VIEWS //视图
　　SELECT from information_schema.TABLES //表

查看触发器
　　SHOW TRIGGERS [FROM db_name] [LIKE expr]
　　SELECT * FROM triggers T WHERE trigger_name=”mytrigger” \G
查看表主键
ELECT column_name FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE table_name='表名' AND constraint_name='PRIMARY'

mysql查看锁表情况
mysql> show status like 'Table%';

+----------------------------+----------+

| Variable_name | Value |

+----------------------------+----------+

| Table_locks_immediate | 105 |

| Table_locks_waited | 3 |

+----------------------------+----------+
Table_locks_immediate 指的是能够立即获得表级锁的次数

Table_locks_waited 指的是不能立即获取表级锁而需要等待的次数
查看正在被锁定的的表

show OPEN TABLES where In_use > 0;
字符匹配查询
select * from test2 where name regexp 'g$';
查询空值
在mysql中，查询某字段为空时，切记不可用 = null，

而是 is null，不为空则是 is not null
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select * from table where column is null;

select * from table where column is not null;

修改表名
alter table h rename hen;把h表名改成hen
使用like查询状态state为Waiting的所有线程
select * from information_schema.processlist where state like '%Waiting%';

建表后添加主键
alter table zhang add primary key(id);