MySQL中的Information_schema介绍

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[TOC]
##介绍
information_schema数据库是在mysql>5.0版本之后产生的一个虚拟数据库，物理上并不存在。
information_schema数据库类似于“数据字典”，提供了访问数据库元数据的方式，即数据的数据。比如数据库名或表名、列类型、访问权限（更细化的访问方式）。
##information_schema所有数据表一揽

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mysql> use information_schema;
Database changed
mysql> show tables;
+---------------------------------------+
| Tables_in_information_schema          |
+---------------------------------------+
| CHARACTER_SETS                        |
| COLLATIONS                            |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS                               |
| COLUMN_PRIVILEGES                     |
| ENGINES                               |
| EVENTS                                |
| FILES                                 |
| GLOBAL_STATUS                         |
| GLOBAL_VARIABLES                      |
| KEY_COLUMN_USAGE                      |
| OPTIMIZER_TRACE                       |
| PARAMETERS                            |
| PARTITIONS                            |
| PLUGINS                               |
| PROCESSLIST                           |
| PROFILING                             |
| REFERENTIAL_CONSTRAINTS               |
| ROUTINES                              |
| SCHEMATA                              |
| SCHEMA_PRIVILEGES                     |
| SESSION_STATUS                        |
| SESSION_VARIABLES                     |
| STATISTICS                            |
| TABLES                                |
| TABLESPACES                           |
| TABLE_CONSTRAINTS                     |
| TABLE_PRIVILEGES                      |
| TRIGGERS                              |
| USER_PRIVILEGES                       |
| VIEWS                                 |
| INNODB_LOCKS                          |
| INNODB_TRX                            |
| INNODB_SYS_DATAFILES                  |
| INNODB_LOCK_WAITS                     |
| INNODB_SYS_TABLESTATS                 |
| INNODB_CMP                            |
| INNODB_METRICS                        |
| INNODB_CMP_RESET                      |
| INNODB_CMP_PER_INDEX                  |
| INNODB_CMPMEM_RESET                   |
| INNODB_FT_DELETED                     |
| INNODB_BUFFER_PAGE_LRU                |
| INNODB_SYS_FOREIGN                    |
| INNODB_SYS_COLUMNS                    |
| INNODB_SYS_INDEXES                    |
| INNODB_FT_DEFAULT_STOPWORD            |
| INNODB_SYS_FIELDS                     |
| INNODB_CMP_PER_INDEX_RESET            |
| INNODB_BUFFER_PAGE                    |
| INNODB_CMPMEM                         |
| INNODB_FT_INDEX_TABLE                 |
| INNODB_FT_BEING_DELETED               |
| INNODB_SYS_TABLESPACES                |
| INNODB_FT_INDEX_CACHE                 |
| INNODB_SYS_FOREIGN_COLS               |
| INNODB_SYS_TABLES                     |
| INNODB_BUFFER_POOL_STATS              |
| INNODB_FT_CONFIG                      |
+---------------------------------------+
59 rows in set (0.00 sec)

共有59张表，但是我们在SQL注入过程中，主要用到其中7张表，最重要的是SCHEMA，TABLES，COLUMNS这三张表。
##重要表结构
###SCHEMATA表
information_schema.SCHEMATA表提供了当前mysql实例中所有数据库的信息。是show databases的结果。

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mysql> select * from information_schema.schemata;
+--------------+--------------------+----------------------------+------------------------+----------+
| CATALOG_NAME | SCHEMA_NAME        | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH |
+--------------+--------------------+----------------------------+------------------------+----------+
| def          | information_schema | utf8                       | utf8_general_ci        | NULL     |
| def          | mysql              | latin1                     | latin1_swedish_ci      | NULL     |
| def          | performance_schema | utf8                       | utf8_general_ci        | NULL     |
| def          | test               | latin1                     | latin1_swedish_ci      | NULL     |
+--------------+--------------------+----------------------------+------------------------+----------+
4 rows in set (0.00 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+
4 rows in set (0.00 sec)

###TABLES表
information_schema.TABLES表提供了关于数据库中的表的信息（包括视图）。是show tables from [schemaname]的结果。

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mysql> desc information_schema.tables;
+-----------------+---------------------+------+-----+---------+-------+
| Field           | Type                | Null | Key | Default | Extra |
+-----------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG   | varchar(512)        | NO   |     |         |       |
| TABLE_SCHEMA    | varchar(64)         | NO   |     |         |       |
| TABLE_NAME      | varchar(64)         | NO   |     |         |       |
| TABLE_TYPE      | varchar(64)         | NO   |     |         |       |
| ENGINE          | varchar(64)         | YES  |     | NULL    |       |
| VERSION         | bigint(21) unsigned | YES  |     | NULL    |       |
| ROW_FORMAT      | varchar(10)         | YES  |     | NULL    |       |
| TABLE_ROWS      | bigint(21) unsigned | YES  |     | NULL    |       |
| AVG_ROW_LENGTH  | bigint(21) unsigned | YES  |     | NULL    |       |
| DATA_LENGTH     | bigint(21) unsigned | YES  |     | NULL    |       |
| MAX_DATA_LENGTH | bigint(21) unsigned | YES  |     | NULL    |       |
| INDEX_LENGTH    | bigint(21) unsigned | YES  |     | NULL    |       |
| DATA_FREE       | bigint(21) unsigned | YES  |     | NULL    |       |
| AUTO_INCREMENT  | bigint(21) unsigned | YES  |     | NULL    |       |
| CREATE_TIME     | datetime            | YES  |     | NULL    |       |
| UPDATE_TIME     | datetime            | YES  |     | NULL    |       |
| CHECK_TIME      | datetime            | YES  |     | NULL    |       |
| TABLE_COLLATION | varchar(32)         | YES  |     | NULL    |       |
| CHECKSUM        | bigint(21) unsigned | YES  |     | NULL    |       |
| CREATE_OPTIONS  | varchar(255)        | YES  |     | NULL    |       |
| TABLE_COMMENT   | varchar(2048)       | NO   |     |         |       |
+-----------------+---------------------+------+-----+---------+-------+
21 rows in set (0.01 sec)

其中，table_schema为数据库名称；table_name为表名；table_rows为该表中的数据行数.
如想通过information_schema查询名为mysql的数据库中所有表：

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mysql> select * from information_schema.tables where table_schema='mysql';
+---------------+--------------+---------------------------+------------+--------+---------+------------+------------+----------------+-------------+--------------------+--------------+-----------+----------------+---------------------+---------------------+---------------------+-------------------+----------+--------------------+-----------------------------------------+
| TABLE_CATALOG | TABLE_SCHEMA | TABLE_NAME                | TABLE_TYPE | ENGINE | VERSION | ROW_FORMAT | TABLE_ROWS | AVG_ROW_LENGTH | DATA_LENGTH | MAX_DATA_LENGTH    | INDEX_LENGTH | DATA_FREE | AUTO_INCREMENT | CREATE_TIME         | UPDATE_TIME         | CHECK_TIME          | TABLE_COLLATION   | CHECKSUM | CREATE_OPTIONS     | TABLE_COMMENT                           |
+---------------+--------------+---------------------------+------------+--------+---------+------------+------------+----------------+-------------+--------------------+--------------+-----------+----------------+---------------------+---------------------+---------------------+-------------------+----------+--------------------+-----------------------------------------+
| def           | mysql        | columns_priv              | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 | 227994731135631359 |         4096 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_bin          |     NULL |                    | Column privileges                       |
| def           | mysql        | db                        | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 | 123848989752688639 |         2048 |         0 |           NULL | 2016-08-30 19:14:48 | 2016-08-30 19:14:48 | NULL                | utf8_bin          |     NULL |                    | Database privileges                     |
| def           | mysql        | event                     | BASE TABLE | MyISAM |      10 | Dynamic    |          0 |              0 |           0 |    281474976710655 |         2048 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_general_ci   |     NULL |                    | Events                                  |
| def           | mysql        | func                      | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 | 162974011515469823 |         1024 |         0 |           NULL | 2016-08-30 19:14:48 | 2016-08-30 19:14:48 | NULL                | utf8_bin          |     NULL |                    | User defined functions                  |
| def           | mysql        | general_log               | BASE TABLE | CSV    |      10 | Dynamic    |          2 |              0 |           0 |                  0 |            0 |         0 |           NULL | NULL                | NULL                | NULL                | utf8_general_ci   |     NULL |                    | General log                             |
| def           | mysql        | help_category             | BASE TABLE | MyISAM |      10 | Dynamic    |         40 |             28 |        1120 |    281474976710655 |         3072 |         0 |           NULL | 2016-08-30 19:14:53 | 2016-08-30 19:14:53 | NULL                | utf8_general_ci   |     NULL |                    | help categories                         |
| def           | mysql        | help_keyword              | BASE TABLE | MyISAM |      10 | Fixed      |        611 |            197 |      120367 |  55450570411999231 |        21504 |         0 |           NULL | 2016-08-30 19:14:53 | 2016-08-30 19:14:53 | NULL                | utf8_general_ci   |     NULL |                    | help keywords                           |
| def           | mysql        | help_relation             | BASE TABLE | MyISAM |      10 | Fixed      |       1218 |              9 |       10962 |   2533274790395903 |        21504 |         0 |           NULL | 2016-08-30 19:14:53 | 2016-08-30 19:14:53 | NULL                | utf8_general_ci   |     NULL |                    | keyword-topic relation                  |
| def           | mysql        | help_topic                | BASE TABLE | MyISAM |      10 | Dynamic    |        583 |            975 |      568664 |    281474976710655 |        22528 |         0 |           NULL | 2016-08-30 19:14:53 | 2016-08-30 19:14:53 | NULL                | utf8_general_ci   |     NULL |                    | help topics                             |
| def           | mysql        | innodb_index_stats        | BASE TABLE | InnoDB |      10 | Compact    |          3 |           5461 |       16384 |                  0 |            0 |         0 |           NULL | 2017-04-19 16:55:05 | NULL                | NULL                | utf8_bin          |     NULL | stats_persistent=0 |                                         |
| def           | mysql        | innodb_table_stats        | BASE TABLE | InnoDB |      10 | Compact    |          1 |          16384 |       16384 |                  0 |            0 |         0 |           NULL | 2017-04-19 16:55:05 | NULL                | NULL                | utf8_bin          |     NULL | stats_persistent=0 |                                         |
| def           | mysql        | ndb_binlog_index          | BASE TABLE | MyISAM |      10 | Dynamic    |          0 |              0 |           0 |    281474976710655 |         1024 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | latin1_swedish_ci |     NULL |                    |                                         |
| def           | mysql        | plugin                    | BASE TABLE | MyISAM |      10 | Dynamic    |          0 |              0 |           0 |    281474976710655 |         1024 |         0 |           NULL | 2016-08-30 19:14:48 | 2016-08-30 19:14:48 | NULL                | utf8_general_ci   |     NULL |                    | MySQL plugins                           |
| def           | mysql        | proc                      | BASE TABLE | MyISAM |      10 | Dynamic    |          0 |              0 |           0 |    281474976710655 |         2048 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_general_ci   |     NULL |                    | Stored Procedures                       |
| def           | mysql        | procs_priv                | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 | 239253730204057599 |         4096 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_bin          |     NULL |                    | Procedure privileges                    |
| def           | mysql        | proxies_priv              | BASE TABLE | MyISAM |      10 | Fixed      |          2 |            693 |        1386 | 195062158860484607 |         5120 |         0 |           NULL | 2016-08-30 19:14:53 | 2016-08-30 19:14:53 | 2016-08-30 19:14:53 | utf8_bin          |     NULL |                    | User proxy privileges                   |
| def           | mysql        | servers                   | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 | 433752939111120895 |         1024 |         0 |           NULL | 2016-08-30 19:14:48 | 2016-08-30 19:14:48 | NULL                | utf8_general_ci   |     NULL |                    | MySQL Foreign Servers table             |
| def           | mysql        | slave_master_info         | BASE TABLE | InnoDB |      10 | Compact    |          0 |              0 |       16384 |                  0 |            0 |         0 |           NULL | 2017-04-19 16:55:05 | NULL                | NULL                | utf8_general_ci   |     NULL | stats_persistent=0 | Master Information                      |
| def           | mysql        | slave_relay_log_info      | BASE TABLE | InnoDB |      10 | Compact    |          0 |              0 |       16384 |                  0 |            0 |         0 |           NULL | 2017-04-19 16:55:05 | NULL                | NULL                | utf8_general_ci   |     NULL | stats_persistent=0 | Relay Log Information                   |
| def           | mysql        | slave_worker_info         | BASE TABLE | InnoDB |      10 | Compact    |          0 |              0 |       16384 |                  0 |            0 |         0 |           NULL | 2017-04-19 16:55:05 | NULL                | NULL                | utf8_general_ci   |     NULL | stats_persistent=0 | Worker Information                      |
| def           | mysql        | slow_log                  | BASE TABLE | CSV    |      10 | Dynamic    |          2 |              0 |           0 |                  0 |            0 |         0 |           NULL | NULL                | NULL                | NULL                | utf8_general_ci   |     NULL |                    | Slow log                                |
| def           | mysql        | tables_priv               | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 | 239535205180768255 |         4096 |         0 |           NULL | 2016-08-30 19:14:48 | 2016-08-30 19:14:48 | NULL                | utf8_bin          |     NULL |                    | Table privileges                        |
| def           | mysql        | time_zone                 | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 |   1970324836974591 |         1024 |         0 |              1 | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_general_ci   |     NULL |                    | Time zones                              |
| def           | mysql        | time_zone_leap_second     | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 |   3659174697238527 |         1024 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_general_ci   |     NULL |                    | Leap seconds information for time zones |
| def           | mysql        | time_zone_name            | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 |  55450570411999231 |         1024 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_general_ci   |     NULL |                    | Time zone names                         |
| def           | mysql        | time_zone_transition      | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 |   4785074604081151 |         1024 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_general_ci   |     NULL |                    | Time zone transitions                   |
| def           | mysql        | time_zone_transition_type | BASE TABLE | MyISAM |      10 | Fixed      |          0 |              0 |           0 |  10696049115004927 |         1024 |         0 |           NULL | 2016-08-30 19:14:49 | 2016-08-30 19:14:49 | NULL                | utf8_general_ci   |     NULL |                    | Time zone transition types              |
| def           | mysql        | user                      | BASE TABLE | MyISAM |      10 | Dynamic    |          5 |             70 |         352 |    281474976710655 |         2048 |         0 |           NULL | 2016-08-30 19:14:48 | 2016-08-30 19:14:55 | NULL                | utf8_bin          |     NULL |                    | Users and global privileges             |
+---------------+--------------+---------------------------+------------+--------+---------+------------+------------+----------------+-------------+--------------------+--------------+-----------+----------------+---------------------+---------------------+---------------------+-------------------+----------+--------------------+-----------------------------------------+
28 rows in set (0.00 sec)

###COLUMNS表
information_schema.COLUMNS表提供了表中的列的信息，详细表述了某张表的所有列以及每个列的信息，是show columns from [schemaname].[tablename]的结果。

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mysql> desc information_schema.COLUMNS;
+--------------------------+---------------------+------+-----+---------+-------+
| Field                    | Type                | Null | Key | Default | Extra |
+--------------------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG            | varchar(512)        | NO   |     |         |       |
| TABLE_SCHEMA             | varchar(64)         | NO   |     |         |       |
| TABLE_NAME               | varchar(64)         | NO   |     |         |       |
| COLUMN_NAME              | varchar(64)         | NO   |     |         |       |
| ORDINAL_POSITION         | bigint(21) unsigned | NO   |     | 0       |       |
| COLUMN_DEFAULT           | longtext            | YES  |     | NULL    |       |
| IS_NULLABLE              | varchar(3)          | NO   |     |         |       |
| DATA_TYPE                | varchar(64)         | NO   |     |         |       |
| CHARACTER_MAXIMUM_LENGTH | bigint(21) unsigned | YES  |     | NULL    |       |
| CHARACTER_OCTET_LENGTH   | bigint(21) unsigned | YES  |     | NULL    |       |
| NUMERIC_PRECISION        | bigint(21) unsigned | YES  |     | NULL    |       |
| NUMERIC_SCALE            | bigint(21) unsigned | YES  |     | NULL    |       |
| DATETIME_PRECISION       | bigint(21) unsigned | YES  |     | NULL    |       |
| CHARACTER_SET_NAME       | varchar(32)         | YES  |     | NULL    |       |
| COLLATION_NAME           | varchar(32)         | YES  |     | NULL    |       |
| COLUMN_TYPE              | longtext            | NO   |     | NULL    |       |
| COLUMN_KEY               | varchar(3)          | NO   |     |         |       |
| EXTRA                    | varchar(30)         | NO   |     |         |       |
| PRIVILEGES               | varchar(80)         | NO   |     |         |       |
| COLUMN_COMMENT           | varchar(1024)       | NO   |     |         |       |
+--------------------------+---------------------+------+-----+---------+-------+
20 rows in set (0.00 sec)

其中，对应information_schema.Tables，多出来的COLUMN_NAME为对应表中的列名。
如想查询表名为user的表中的所有列名：

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mysql> select * from information_schema.columns where table_name='user';
+---------------+--------------+------------+------------------------+------------------+-----------------------+-------------+-----------+--------------------------+------------------------+-------------------+---------------+--------------------+--------------------+-----------------+-----------------------------------+------------+-------+---------------------------------+----------------+
| TABLE_CATALOG | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME            | ORDINAL_POSITION | COLUMN_DEFAULT        | IS_NULLABLE | DATA_TYPE | CHARACTER_MAXIMUM_LENGTH | CHARACTER_OCTET_LENGTH | NUMERIC_PRECISION | NUMERIC_SCALE | DATETIME_PRECISION | CHARACTER_SET_NAME | COLLATION_NAME  | COLUMN_TYPE                       | COLUMN_KEY | EXTRA | PRIVILEGES                      | COLUMN_COMMENT |
+---------------+--------------+------------+------------------------+------------------+-----------------------+-------------+-----------+--------------------------+------------------------+-------------------+---------------+--------------------+--------------------+-----------------+-----------------------------------+------------+-------+---------------------------------+----------------+
| def           | mysql        | user       | Host                   |                1 |                       | NO          | char      |                       60 |                    180 |              NULL |          NULL |               NULL | utf8               | utf8_bin        | char(60)                          | PRI        |       | select,insert,update,references |                |
| def           | mysql        | user       | User                   |                2 |                       | NO          | char      |                       16 |                     48 |              NULL |          NULL |               NULL | utf8               | utf8_bin        | char(16)                          | PRI        |       | select,insert,update,references |                |
| def           | mysql        | user       | Password               |                3 |                       | NO          | char      |                       41 |                     41 |              NULL |          NULL |               NULL | latin1             | latin1_bin      | char(41)                          |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Select_priv            |                4 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Insert_priv            |                5 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Update_priv            |                6 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Delete_priv            |                7 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Create_priv            |                8 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Drop_priv              |                9 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Reload_priv            |               10 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Shutdown_priv          |               11 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Process_priv           |               12 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | File_priv              |               13 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Grant_priv             |               14 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | References_priv        |               15 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Index_priv             |               16 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Alter_priv             |               17 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Show_db_priv           |               18 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Super_priv             |               19 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Create_tmp_table_priv  |               20 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Lock_tables_priv       |               21 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Execute_priv           |               22 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Repl_slave_priv        |               23 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Repl_client_priv       |               24 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Create_view_priv       |               25 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Show_view_priv         |               26 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Create_routine_priv    |               27 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Alter_routine_priv     |               28 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Create_user_priv       |               29 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Event_priv             |               30 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Trigger_priv           |               31 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | Create_tablespace_priv |               32 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
| def           | mysql        | user       | ssl_type               |               33 |                       | NO          | enum      |                        9 |                     27 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('','ANY','X509','SPECIFIED') |            |       | select,insert,update,references |                |
| def           | mysql        | user       | ssl_cipher             |               34 | NULL                  | NO          | blob      |                    65535 |                  65535 |              NULL |          NULL |               NULL | NULL               | NULL            | blob                              |            |       | select,insert,update,references |                |
| def           | mysql        | user       | x509_issuer            |               35 | NULL                  | NO          | blob      |                    65535 |                  65535 |              NULL |          NULL |               NULL | NULL               | NULL            | blob                              |            |       | select,insert,update,references |                |
| def           | mysql        | user       | x509_subject           |               36 | NULL                  | NO          | blob      |                    65535 |                  65535 |              NULL |          NULL |               NULL | NULL               | NULL            | blob                              |            |       | select,insert,update,references |                |
| def           | mysql        | user       | max_questions          |               37 | 0                     | NO          | int       |                     NULL |                   NULL |                10 |             0 |               NULL | NULL               | NULL            | int(11) unsigned                  |            |       | select,insert,update,references |                |
| def           | mysql        | user       | max_updates            |               38 | 0                     | NO          | int       |                     NULL |                   NULL |                10 |             0 |               NULL | NULL               | NULL            | int(11) unsigned                  |            |       | select,insert,update,references |                |
| def           | mysql        | user       | max_connections        |               39 | 0                     | NO          | int       |                     NULL |                   NULL |                10 |             0 |               NULL | NULL               | NULL            | int(11) unsigned                  |            |       | select,insert,update,references |                |
| def           | mysql        | user       | max_user_connections   |               40 | 0                     | NO          | int       |                     NULL |                   NULL |                10 |             0 |               NULL | NULL               | NULL            | int(11) unsigned                  |            |       | select,insert,update,references |                |
| def           | mysql        | user       | plugin                 |               41 | mysql_native_password | YES         | char      |                       64 |                    192 |              NULL |          NULL |               NULL | utf8               | utf8_bin        | char(64)                          |            |       | select,insert,update,references |                |
| def           | mysql        | user       | authentication_string  |               42 | NULL                  | YES         | text      |                    65535 |                  65535 |              NULL |          NULL |               NULL | utf8               | utf8_bin        | text                              |            |       | select,insert,update,references |                |
| def           | mysql        | user       | password_expired       |               43 | N                     | NO          | enum      |                        1 |                      3 |              NULL |          NULL |               NULL | utf8               | utf8_general_ci | enum('N','Y')                     |            |       | select,insert,update,references |                |
+---------------+--------------+------------+------------------------+------------------+-----------------------+-------------+-----------+--------------------------+------------------------+-------------------+---------------+--------------------+--------------------+-----------------+-----------------------------------+------------+-------+---------------------------------+----------------+
43 rows in set (0.00 sec)

###权限表
权限表主要有三个，分别为USER_PRIVILEGES表、SCHEMA_PRIVILEGES表、TABLE_PRIVILEGES表和COLUMN_PRIVILEGES表。学习方法同上！
##总结
通过information_schema表,我们可以在不知道数据库名、表名、列名的情况下进行数据查询。