MySQL INFORMATION_SCHEMA 使用

-- 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 = (‘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
FROM
    information_schema.TABLES
ORDER BY data_length DESC;

MySQL INFORMATION_SCHEMA 使用

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