mysql

查看所以庫大小
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;

查詢 表結構
show create tables tablename
查詢視圖結構
show create view viem.name
查詢數據庫中的存儲過程和函數

   select `name` from mysql.proc where db = 'xx' and `type` = 'PROCEDURE'   //存儲過程
   select `name` from mysql.proc where db = 'xx' and `type` = 'FUNCTION'   //函數

   show procedure status; //存儲過程
   show function status;     //函數

查看存儲過程或函數的創建代碼

　　show create procedure proc_name;
　　show create function func_name;

查看視圖
　　SELECT from information_schema.VIEWS //視圖
　　SELECT from information_schema.TABLES //表

查看觸發器
　　SHOW TRIGGERS [FROM db_name] [LIKE expr]
　　SELECT * FROM triggers T WHERE trigger_name=”mytrigger” \G
查看錶主鍵
ELECT column_name FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE table_name='表名' AND constraint_name='PRIMARY'

mysql查看鎖表情況
mysql> show status like 'Table%';

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

| Variable_name | Value |

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

| Table_locks_immediate | 105 |

| Table_locks_waited | 3 |

+----------------------------+----------+
Table_locks_immediate 指的是能夠立即獲得表級鎖的次數

Table_locks_waited 指的是不能立即獲取表級鎖而需要等待的次數
查看正在被鎖定的的表

show OPEN TABLES where In_use > 0;
字符匹配查詢
select * from test2 where name regexp 'g$';
查詢空值
在mysql中，查詢某字段爲空時，切記不可用 = null，

而是 is null，不爲空則是 is not null
www.2cto.com
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查詢狀態state爲Waiting的所有線程
select * from information_schema.processlist where state like '%Waiting%';

建表後添加主鍵
alter table zhang add primary key(id);