MySQL INFORMATION_SCHEMA 使用

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
FROM
    INFORMATION_SCHEMA.TABLES T1,
    INFORMATION_SCHEMA.STATISTICS T2
WHERE
    T1.TABLE_SCHEMA = T2.TABLE_SCHEMA
        AND T1.TABLE_NAME = T2.TABLE_NAME
        AND T2.SEQ_IN_INDEX = (SELECT 
            MIN(T3.SEQ_IN_INDEX)
        FROM
            INFORMATION_SCHEMA.STATISTICS T3
        WHERE
                T2.TABLE_NAME = T3.TABLE_NAME
                AND T2.TABLE_SCHEMA = T3.TABLE_SCHEMA
                AND 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
FROM
    information_schema.innodb_lock_waits t1,
    information_schema.innodb_trx t2,
    information_schema.innodb_trx t3
WHERE
    t1.blocking_trx_id = t2.trx_id
        AND 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
FROM
    INFORMATION_SCHEMA.TABLES
WHERE
    TABLE_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_sql
  FROM INFORMATION_SCHEMA.TABLES
 WHERE 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
FROM
    information_schema.tables
WHERE
    table_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
FROM
    performance_schema.threads
WHERE
    type = '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
FROM
    INFORMATION_SCHEMA.COLUMNS
WHERE
    table_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
FROM
    INFORMATION_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
FROM
    information_schema.KEY_COLUMN_USAGE
WHERE
    REFERENCED_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
FROM
    information_schema.PARTITIONS
WHERE
    table_schema = 'test'
        AND table_name = 't';

-- 查看支持的插件

SELECT
  PLUGIN_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
FROM
    INFORMATION_SCHEMA.ROUTINES
WHERE
    ROUTINE_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
FROM
    INFORMATION_SCHEMA.SCHEMATA;

SHOW DATABASES;

-- 查看索引信息

SELECT 
    table_schema,
    table_name,
    index_name,
    COLUMN_NAME,
    COLLATION,
    CARDINALITY,
    index_type
FROM
    INFORMATION_SCHEMA.STATISTICS
WHERE
    table_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
FROM
    information_schema.TABLES
WHERE
    ENGINE 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