一、INFORMATION_SCHEMA介绍
第一个查询看看库里有多少个表,表名等
select * from INFORMATION_SCHEMA.TABLES
information_schema这张数据表保存了MySQL服务器所有数据库的信息。如数据库名,数据库的表,表栏的数据类型与访问权限等。再简单点,这台mysql服务器上,到底有哪些数据库、各个数据库有哪些表,每张表的字段类型是什么,各个数据库要什么权限才能访问,等等信息都保存在information_schema表里面。
Mysql的INFORMATION_SCHEMA数据库包含了一些表和视图,提供了访问数据库元数据的方式。
元数据是关于数据的数据,如数据库名或表名,列的数据类型,或访问权限等。有些时候用于表述该信息的其他术语包括“数据词典”和“系统目录”。
下面对一些重要的数据字典表做一些说明:
SCHEMATA表:提供了关于数据库的信息。
TABLES表:给出了关于数据库中的表的信息。
COLUMNS表:给出了表中的列信息。
STATISTICS表:给出了关于表索引的信息。
USER_PRIVILEGES表:给出了关于全程权限的信息。该信息源自mysql.user授权表。
SCHEMA_PRIVILEGES表:给出了关于方案(数据库)权限的信息。该信息来自mysql.db授权表。
TABLE_PRIVILEGES表:给出了关于表权限的信息。该信息源自mysql.tables_priv授权表。
COLUMN_PRIVILEGES表:给出了关于列权限的信息。该信息源自mysql.columns_priv授权表。
CHARACTER_SETS表:提供了关于可用字符集的信息。
COLLATIONS表:提供了关于各字符集的对照信息。
COLLATION_CHARACTER_SET_APPLICABILITY表:指明了可用于校对的字符集。
TABLE_CONSTRAINTS表:描述了存在约束的表。
KEY_COLUMN_USAGE表:描述了具有约束的键列。
ROUTINES表:提供了关于存储子程序(存储程序和函数)的信息。此时,ROUTINES表不包含自定义函数(UDF)。
VIEWS表:给出了关于数据库中的视图的信息。
TRIGGERS表:提供了关于触发程序的信息。
二、使用示例
--查看创建的索引的CARDINALITY比率
--通常cardinality达到表数据的10%左右建索引会有意义
--如果是一个组合索引,索引第一位的cardinality表示第一个列的cardinality大小,第二列表示第一列和第二列共同的cardinality值
SELECT T1.TABLE_SCHEMA,T1.TABLE_NAME,T2.INDEX_NAME,ROUND(T2.CARDINALITY / T1.TABLE_ROWS * 100, 2) AS RATE FROMINFORMATION_SCHEMA.TABLES T1,INFORMATION_SCHEMA.STATISTICS T2 WHERET1.TABLE_SCHEMA = T2.TABLE_SCHEMAAND T1.TABLE_NAME = T2.TABLE_NAMEAND T2.SEQ_IN_INDEX = (SELECT MIN(T3.SEQ_IN_INDEX)FROMINFORMATION_SCHEMA.STATISTICS T3WHERET2.TABLE_NAME = T3.TABLE_NAMEAND T2.TABLE_SCHEMA = T3.TABLE_SCHEMAAND T2.INDEX_NAME = T3.INDEX_NAME) AND T1.TABLE_SCHEMA NOT IN ('MYSQL','PERFORMANCE_SCHEMA','INFORMATION_SCHEMA','SYS') AND T1.TABLE_ROWS >=100 ORDER BY RATE;
--查看锁阻塞
-- 查看锁的SQL SELECT t3.trx_id waiting_trx_id,t3.trx_mysql_thread_id waiting_thread,t3.trx_query waiting_query,t2.trx_id blocking_trx_id,t2.trx_mysql_thread_id blocking_thread,t2.trx_query blocking_query FROMinformation_schema.innodb_lock_waits t1,information_schema.innodb_trx t2,information_schema.innodb_trx t3 WHEREt1.blocking_trx_id = t2.trx_idAND t1.requesting_trx_id = t3.trx_id;
--查询出哪些表不是InnoDB引擎的
SELECT TABLE_SCHEMA,TABLE_NAME,TABLE_TYPE,ENGINE,CREATE_TIME,UPDATE_TIME,TABLE_COLLATION FROMINFORMATION_SCHEMA.TABLES WHERETABLE_SCHEMA NOT IN ('information_schema' , 'mysql', 'performance_schema', 'sys')AND ENGINE <> 'InnoDB';
--生成修改存储引擎的语句
SELECT -- TABLE_SCHEMA,-- TABLE_NAME,-- TABLE_TYPE,-- ENGINE,-- CREATE_TIME,-- UPDATE_TIME,-- TABLE_COLLATION,CONCAT('alter table ', TABLE_SCHEMA,'.',TABLE_NAME, ' engine=InnoDB;') AS alter_sqlFROM INFORMATION_SCHEMA.TABLESWHERE TABLE_SCHEMA NOT IN('information_schema', 'mysql', 'performance_schema', 'sys')AND ENGINE <> 'InnoDB';
-- 查看指定数据库的表信息
SET @table_schema='employees'; SELECT table_name,table_type,engine,table_rows,avg_row_length,data_length,index_length,table_collation,create_time FROMinformation_schema.tables WHEREtable_schema = @table_schema ORDER BY table_name;
-- 查看会话连接信息
SELECT THREAD_ID,name,type,PROCESSLIST_ID,PROCESSLIST_USER AS user,PROCESSLIST_HOST AS host,PROCESSLIST_DB AS db,PROCESSLIST_COMMAND AS cmd,PROCESSLIST_TIME AS time,PROCESSLIST_STATE AS state,PROCESSLIST_INFO AS info,CONNECTION_TYPE AS type,THREAD_OS_ID AS os_id FROMperformance_schema.threads WHEREtype = 'FOREGROUND' ORDER BY THREAD_ID;
-- CHARACTER_SETS 查看数据库支持的字符集
SELECT * FROM INFORMATION_SCHEMA.CHARACTER_SETS WHERE CHARACTER_SET_NAME LIKE 'utf%';SHOW CHARACTER SET LIKE 'utf%';
-- COLLATIONS 字符序
-- 用于指定数据集如何排序,以及字符串的比对规则 SELECT * FROM INFORMATION_SCHEMA.COLLATIONS WHERE COLLATION_NAME LIKE 'utf%';SHOW COLLATION LIKE 'utf%';
-- 查看表结构定义信息
SELECT table_name,COLUMN_NAME,ordinal_position,DATA_TYPE,IS_NULLABLE,COLUMN_DEFAULT,column_type,column_key,character_set_name,collation_name FROMINFORMATION_SCHEMA.COLUMNS WHEREtable_name = 'employees'AND table_schema = 'employees';
show columns from employees from employees;
desc employeees.employees;
-- 查看支持的引擎
SELECT * FROM INFORMATION_SCHEMA.ENGINES; show ENGINES;
-- 查看数据库的数据文件信息
SELECT FILE_ID,FILE_NAME,FILE_TYPE,TABLESPACE_NAME,FREE_EXTENTS,TOTAL_EXTENTS,((TOTAL_EXTENTS - FREE_EXTENTS) * EXTENT_SIZE) / 1024 / 1024 AS MB_used,EXTENT_SIZE,INITIAL_SIZE,MAXIMUM_SIZE,AUTOEXTEND_SIZE,DATA_FREE,STATUS,ENGINE FROMINFORMATION_SCHEMA.FILES;
-- 查看指定表的约束
SELECT constraint_schema,table_name,constraint_name,column_name,ordinal_position,CONCAT(table_name,'.',column_name,' -> ',referenced_table_name,'.',referenced_column_name) AS list_of_fks FROMinformation_schema.KEY_COLUMN_USAGE WHEREREFERENCED_TABLE_SCHEMA = 'employees'AND REFERENCED_TABLE_NAME IS NOT NULL ORDER BY TABLE_NAME , COLUMN_NAME;
-- 查看指定分区表信息
SELECT TABLE_SCHEMA,table_name,partition_name,subpartition_name sub_par,partition_ordinal_position par_position,partition_method method,partition_expression expression,partition_description description,table_rows FROMinformation_schema.PARTITIONS WHEREtable_schema = 'test'AND table_name = 't';
-- 查看支持的插件
SELECTPLUGIN_NAME, PLUGIN_STATUS, PLUGIN_TYPE,PLUGIN_LIBRARY, PLUGIN_LICENSE FROM INFORMATION_SCHEMA.PLUGINS;SHOW PLUGINS;
-- 查看数据库连接信息
SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST;SHOW FULL PROCESSLIST;
-- 查看数据库中的存储过程、函数等
SELECT ROUTINE_SCHEMA,routine_name,ROUTINE_TYPE,data_type,routine_body,routine_definition,routine_comment FROMINFORMATION_SCHEMA.ROUTINES WHEREROUTINE_TYPE = 'PROCEDURE' AND ROUTINE_SCHEMA="employees";
-- 查看存在的数据库及字符集信息
SELECT SCHEMA_NAME,DEFAULT_CHARACTER_SET_NAME,DEFAULT_COLLATION_NAME FROMINFORMATION_SCHEMA.SCHEMATA;SHOW DATABASES;
-- 查看索引信息
SELECT table_schema,table_name,index_name,COLUMN_NAME,COLLATION,CARDINALITY,index_type FROMINFORMATION_SCHEMA.STATISTICS WHEREtable_name = 'employees'AND table_schema = 'employees';
SHOW INDEX FROM employees FROM employees;
-- 查看数据库大小
SELECT table_schema 'database',CONCAT(ROUND(SUM(data_length + index_length) / (1024 * 1024),2),'M') size FROMinformation_schema.TABLES WHEREENGINE in ('MyISAM','InnoDB') GROUP BY table_schema;
-- 查看表大小
SELECT
CONCAT(table_schema, '.', table_name) table_name,
CONCAT(ROUND(data_length / (1024 * 1024), 2),
'M') data_length,
CONCAT(ROUND(index_length / (1024 * 1024), 2),
'M') index_length,
CONCAT(ROUND(ROUND(data_length + index_length) / (1024 * 1024),
2),
'M') total_size,
engine
FROM
information_schema.TABLES
WHERE
table_schema NOT IN ('information_schema' , 'performance_schema', 'sys', 'mysql')
ORDER BY data_length DESC;
转自:http://www.cnblogs.com/zhenxing/p/5340592.html