Information Schema

Information Schema

为了和 MySQL 保持兼容，TiDB 支持很多 INFORMATION\_SCHEMA 表，其中有不少表都支持相应的 SHOW 命令。查询 INFORMATION_SCHEMA 表也为表的连接操作提供了可能。

CHARACTER_SETS Table

CHARACTER_SETS 表提供字符集相关的信息。TiDB 目前仅支持部分字符集。

mysql> SELECT * FROM character_sets;
+--+-++--+
| CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME | DESCRIPTION   | MAXLEN |
+--+-++--+
| utf8               | utf8_bin             | UTF-8 Unicode |      3 |
| utf8mb4            | utf8mb4_bin          | UTF-8 Unicode |      4 |
| ascii              | ascii_bin            | US ASCII      |      1 |
| latin1             | latin1_bin           | Latin1        |      1 |
| binary             | binary               | binary        |      1 |
+--+-++--+
5 rows in set (0.00 sec)

COLLATIONS Table

COLLATIONS 表提供了 CHARACTER_SETS 表中字符集对应的排序规则列表。TiDB 当前仅支持二进制排序规则，包含该表仅为兼容 MySQL。

mysql> SELECT * FROM collations WHERE character_set_name='utf8mb4';
++--+++-++
| COLLATION_NAME         | CHARACTER_SET_NAME | ID   | IS_DEFAULT | IS_COMPILED | SORTLEN |
++--+++-++
| utf8mb4_general_ci     | utf8mb4            |   45 | Yes        | Yes         |       1 |
| utf8mb4_bin            | utf8mb4            |   46 |            | Yes         |       1 |
| utf8mb4_unicode_ci     | utf8mb4            |  224 |            | Yes         |       1 |
| utf8mb4_icelandic_ci   | utf8mb4            |  225 |            | Yes         |       1 |
| utf8mb4_latvian_ci     | utf8mb4            |  226 |            | Yes         |       1 |
| utf8mb4_romanian_ci    | utf8mb4            |  227 |            | Yes         |       1 |
| utf8mb4_slovenian_ci   | utf8mb4            |  228 |            | Yes         |       1 |
| utf8mb4_polish_ci      | utf8mb4            |  229 |            | Yes         |       1 |
| utf8mb4_estonian_ci    | utf8mb4            |  230 |            | Yes         |       1 |
| utf8mb4_spanish_ci     | utf8mb4            |  231 |            | Yes         |       1 |
| utf8mb4_swedish_ci     | utf8mb4            |  232 |            | Yes         |       1 |
| utf8mb4_turkish_ci     | utf8mb4            |  233 |            | Yes         |       1 |
| utf8mb4_czech_ci       | utf8mb4            |  234 |            | Yes         |       1 |
| utf8mb4_danish_ci      | utf8mb4            |  235 |            | Yes         |       1 |
| utf8mb4_lithuanian_ci  | utf8mb4            |  236 |            | Yes         |       1 |
| utf8mb4_slovak_ci      | utf8mb4            |  237 |            | Yes         |       1 |
| utf8mb4_spanish2_ci    | utf8mb4            |  238 |            | Yes         |       1 |
| utf8mb4_roman_ci       | utf8mb4            |  239 |            | Yes         |       1 |
| utf8mb4_persian_ci     | utf8mb4            |  240 |            | Yes         |       1 |
| utf8mb4_esperanto_ci   | utf8mb4            |  241 |            | Yes         |       1 |
| utf8mb4_hungarian_ci   | utf8mb4            |  242 |            | Yes         |       1 |
| utf8mb4_sinhala_ci     | utf8mb4            |  243 |            | Yes         |       1 |
| utf8mb4_german2_ci     | utf8mb4            |  244 |            | Yes         |       1 |
| utf8mb4_croatian_ci    | utf8mb4            |  245 |            | Yes         |       1 |
| utf8mb4_unicode_520_ci | utf8mb4            |  246 |            | Yes         |       1 |
| utf8mb4_vietnamese_ci  | utf8mb4            |  247 |            | Yes         |       1 |
++--+++-++
26 rows in set (0.00 sec)

COLLATION_CHARACTER_SET_APPLICABILITY Table

COLLATION_CHARACTER_SET_APPLICABILITY 表将排序规则映射至适用的字符集名称。和 COLLATIONS 表一样，包含此表也是为了兼容 MySQL。

mysql> SELECT * FROM collation_character_set_applicability WHERE character_set_name='utf8mb4';
++--+
| COLLATION_NAME         | CHARACTER_SET_NAME |
++--+
| utf8mb4_general_ci     | utf8mb4            |
| utf8mb4_bin            | utf8mb4            |
| utf8mb4_unicode_ci     | utf8mb4            |
| utf8mb4_icelandic_ci   | utf8mb4            |
| utf8mb4_latvian_ci     | utf8mb4            |
| utf8mb4_romanian_ci    | utf8mb4            |
| utf8mb4_slovenian_ci   | utf8mb4            |
| utf8mb4_polish_ci      | utf8mb4            |
| utf8mb4_estonian_ci    | utf8mb4            |
| utf8mb4_spanish_ci     | utf8mb4            |
| utf8mb4_swedish_ci     | utf8mb4            |
| utf8mb4_turkish_ci     | utf8mb4            |
| utf8mb4_czech_ci       | utf8mb4            |
| utf8mb4_danish_ci      | utf8mb4            |
| utf8mb4_lithuanian_ci  | utf8mb4            |
| utf8mb4_slovak_ci      | utf8mb4            |
| utf8mb4_spanish2_ci    | utf8mb4            |
| utf8mb4_roman_ci       | utf8mb4            |
| utf8mb4_persian_ci     | utf8mb4            |
| utf8mb4_esperanto_ci   | utf8mb4            |
| utf8mb4_hungarian_ci   | utf8mb4            |
| utf8mb4_sinhala_ci     | utf8mb4            |
| utf8mb4_german2_ci     | utf8mb4            |
| utf8mb4_croatian_ci    | utf8mb4            |
| utf8mb4_unicode_520_ci | utf8mb4            |
| utf8mb4_vietnamese_ci  | utf8mb4            |
++--+
26 rows in set (0.00 sec)

COLUMNS Table

COLUMNS 表提供了表的所有列的信息。

mysql> CREATE TABLE test.t1 (a int);
1 row in set (0.01 sec)
mysql> SELECT * FROM information_schema.columns WHERE table_schema='test' AND TABLE_NAME='t1'\G
*************************** 1. row ***************************
           TABLE_CATALOG: def
            TABLE_SCHEMA: test
              TABLE_NAME: t1
             COLUMN_NAME: a
        ORDINAL_POSITION: 1
          COLUMN_DEFAULT: NULL
             IS_NULLABLE: YES
               DATA_TYPE: int
CHARACTER_MAXIMUM_LENGTH: NULL
  CHARACTER_OCTET_LENGTH: NULL
       NUMERIC_PRECISION: 11
           NUMERIC_SCALE: 0
      DATETIME_PRECISION: NULL
      CHARACTER_SET_NAME: NULL
          COLLATION_NAME: NULL
             COLUMN_TYPE: int(11)
              COLUMN_KEY: 
                   EXTRA: 
              PRIVILEGES: select,insert,update,references
          COLUMN_COMMENT: 
   GENERATION_EXPRESSION: 
1 row in set (0.01 sec)

对应的 SHOW 语句如下：

mysql> SHOW COLUMNS FROM t1 FROM test;
+-+++++-+
| Field | Type    | Null | Key  | Default | Extra |
+-+++++-+
| a     | int(11) | YES  |      | NULL    |       |
+-+++++-+
1 row in set (0.00 sec)

ENGINES Table

ENGINES 表提供了关于存储引擎的信息。从和 MySQL 兼容性上考虑，TiDB 会一直将 InnoDB 描述为唯一支持的引擎。

mysql> SELECT * FROM engines\G
*************************** 1. row ***************************
      ENGINE: InnoDB
     SUPPORT: DEFAULT
     COMMENT: Supports transactions, row-level locking, and foreign keys
TRANSACTIONS: YES
          XA: YES
  SAVEPOINTS: YES
1 row in set (0.00 sec)

KEY_COLUMN_USAGE Table

KEY_COLUMN_USAGE 表描述了列的键约束，比如主键约束。

mysql> SELECT * FROM key_column_usage WHERE table_schema='mysql' and table_name='user'\G
*************************** 1. row ***************************
           CONSTRAINT_CATALOG: def
            CONSTRAINT_SCHEMA: mysql
              CONSTRAINT_NAME: PRIMARY
                TABLE_CATALOG: def
                 TABLE_SCHEMA: mysql
                   TABLE_NAME: user
                  COLUMN_NAME: Host
             ORDINAL_POSITION: 1
POSITION_IN_UNIQUE_CONSTRAINT: NULL
      REFERENCED_TABLE_SCHEMA: NULL
        REFERENCED_TABLE_NAME: NULL
       REFERENCED_COLUMN_NAME: NULL
*************************** 2. row ***************************
           CONSTRAINT_CATALOG: def
            CONSTRAINT_SCHEMA: mysql
              CONSTRAINT_NAME: PRIMARY
                TABLE_CATALOG: def
                 TABLE_SCHEMA: mysql
                   TABLE_NAME: user
                  COLUMN_NAME: User
             ORDINAL_POSITION: 2
POSITION_IN_UNIQUE_CONSTRAINT: NULL
      REFERENCED_TABLE_SCHEMA: NULL
        REFERENCED_TABLE_NAME: NULL
       REFERENCED_COLUMN_NAME: NULL
2 rows in set (0.00 sec)

SCHEMATA Table

SCHEMATA 表提供了关于数据库的信息。表中的数据与 SHOW DATABASES 语句的执行结果等价。

mysql> SELECT * FROM schemata; 
+--+--+-++-+ 
| CATALOG_NAME | SCHEMA_NAME        | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH | 
+--+--+-++-+ 
| def          | INFORMATION_SCHEMA | utf8mb4                    | utf8mb4_bin            | NULL     | 
| def          | mynewdb            | utf8mb4                    | utf8mb4_bin            | NULL     |
| def          | mysql              | utf8mb4                    | utf8mb4_bin            | NULL     | 
| def          | PERFORMANCE_SCHEMA | utf8mb4                    | utf8mb4_bin            | NULL     | 
| def          | test               | utf8mb4                    | utf8mb4_bin            | NULL     | 
+--+--+-++-+ 
5 rows in set (0.00 sec)

SESSION_VARIABLES Table

SESSION\_VARIABLES 表提供了关于 session 变量的信息。表中的数据跟 SHOW SESSION VARIABLES 语句执行结果类似。

mysql> SELECT * FROM session_variables LIMIT 10;
+-+-+
| VARIABLE_NAME                    | VARIABLE_VALUE       |
+-+-+
| max_write_lock_count             | 18446744073709551615 |
| server_id_bits                   | 32                   |
| net_read_timeout                 | 30                   |
| innodb_online_alter_log_max_size | 134217728            |
| innodb_optimize_fulltext_only    | OFF                  |
| max_join_size                    | 18446744073709551615 |
| innodb_read_io_threads           | 4                    |
| session_track_gtids              | OFF                  |
| have_ssl                         | DISABLED             |
| max_binlog_cache_size            | 18446744073709547520 |
+-+-+
10 rows in set (0.00 sec)

STATISTICS Table

STATISTICS 表提供了关于表索引的信息。

mysql> desc statistics;
+|||||-+
| Field         | Type                | Null | Key  | Default | Extra |
+|||||-+
| TABLE_CATALOG | varchar(512)        | YES  |      | NULL    |       |
| TABLE_SCHEMA  | varchar(64)         | YES  |      | NULL    |       |
| TABLE_NAME    | varchar(64)         | YES  |      | NULL    |       |
| NON_UNIQUE    | varchar(1)          | YES  |      | NULL    |       |
| INDEX_SCHEMA  | varchar(64)         | YES  |      | NULL    |       |
| INDEX_NAME    | varchar(64)         | YES  |      | NULL    |       |
| SEQ_IN_INDEX  | bigint(2) UNSIGNED  | YES  |      | NULL    |       |
| COLUMN_NAME   | varchar(21)         | YES  |      | NULL    |       |
| COLLATION     | varchar(1)          | YES  |      | NULL    |       |
| CARDINALITY   | bigint(21) UNSIGNED | YES  |      | NULL    |       |
| SUB_PART      | bigint(3) UNSIGNED  | YES  |      | NULL    |       |
| PACKED        | varchar(10)         | YES  |      | NULL    |       |
| NULLABLE      | varchar(3)          | YES  |      | NULL    |       |
| INDEX_TYPE    | varchar(16)         | YES  |      | NULL    |       |
| COMMENT       | varchar(16)         | YES  |      | NULL    |       |
| INDEX_COMMENT | varchar(1024)       | YES  |      | NULL    |       |
+|||||-+

下列语句是等价的：

SELECT * FROM INFORMATION_SCHEMA.STATISTICS
  WHERE table_name = 'tbl_name'
  AND table_schema = 'db_name'
SHOW INDEX
  FROM tbl_name
  FROM db_name

TABLES Table

TABLES 表提供了数据库里面关于表的信息。

mysql> SELECT * FROM tables WHERE table_schema='mysql' AND table_name='user'\G
*************************** 1. row ***************************
  TABLE_CATALOG: def
   TABLE_SCHEMA: mysql
     TABLE_NAME: user
     TABLE_TYPE: BASE TABLE
         ENGINE: InnoDB
        VERSION: 10
     ROW_FORMAT: Compact
     TABLE_ROWS: 0
 AVG_ROW_LENGTH: 0
    DATA_LENGTH: 0
MAX_DATA_LENGTH: 0
   INDEX_LENGTH: 0
      DATA_FREE: 0
 AUTO_INCREMENT: 0
    CREATE_TIME: 2019-03-29 09:17:27
    UPDATE_TIME: NULL
     CHECK_TIME: NULL
TABLE_COLLATION: utf8mb4_bin
       CHECKSUM: NULL
 CREATE_OPTIONS: 
  TABLE_COMMENT: 
  TIDB_TABLE_ID: 5
1 row in set (0.00 sec)

以下操作是等价的：

SELECT table_name FROM INFORMATION_SCHEMA.TABLES
  WHERE table_schema = 'db_name'
  [AND table_name LIKE 'wild']
SHOW TABLES
  FROM db_name
  [LIKE 'wild']

TABLE_CONSTRAINTS Table

TABLE\_CONSTRAINTS 表记录了表的约束信息。

mysql> SELECT * FROM table_constraints WHERE constraint_type='UNIQUE'\G
*************************** 1. row ***************************
CONSTRAINT_CATALOG: def
 CONSTRAINT_SCHEMA: mysql
   CONSTRAINT_NAME: name
      TABLE_SCHEMA: mysql
        TABLE_NAME: help_topic
   CONSTRAINT_TYPE: UNIQUE
*************************** 2. row ***************************
CONSTRAINT_CATALOG: def
 CONSTRAINT_SCHEMA: mysql
   CONSTRAINT_NAME: tbl
      TABLE_SCHEMA: mysql
        TABLE_NAME: stats_meta
   CONSTRAINT_TYPE: UNIQUE
*************************** 3. row ***************************
CONSTRAINT_CATALOG: def
 CONSTRAINT_SCHEMA: mysql
   CONSTRAINT_NAME: tbl
      TABLE_SCHEMA: mysql
        TABLE_NAME: stats_histograms
   CONSTRAINT_TYPE: UNIQUE
*************************** 4. row ***************************
CONSTRAINT_CATALOG: def
 CONSTRAINT_SCHEMA: mysql
   CONSTRAINT_NAME: tbl
      TABLE_SCHEMA: mysql
        TABLE_NAME: stats_buckets
   CONSTRAINT_TYPE: UNIQUE
*************************** 5. row ***************************
CONSTRAINT_CATALOG: def
 CONSTRAINT_SCHEMA: mysql
   CONSTRAINT_NAME: delete_range_index
      TABLE_SCHEMA: mysql
        TABLE_NAME: gc_delete_range
   CONSTRAINT_TYPE: UNIQUE
*************************** 6. row ***************************
CONSTRAINT_CATALOG: def
 CONSTRAINT_SCHEMA: mysql
   CONSTRAINT_NAME: delete_range_done_index
      TABLE_SCHEMA: mysql
        TABLE_NAME: gc_delete_range_done
   CONSTRAINT_TYPE: UNIQUE
6 rows in set (0.00 sec)

其中：

CONSTRAINT_TYPE 的取值可以是 UNIQUE，PRIMARY KEY，或者 FOREIGN KEY。
UNIQUE 和 PRIMARY KEY 信息与 SHOW INDEX 语句的执行结果类似。

USER_PRIVILEGES Table

USER_PRIVILEGES 表提供了关于全局权限的信息。该表的数据根据 mysql.user 系统表生成。

mysql> desc USER_PRIVILEGES;
+-|--||||-+
| Field          | Type         | Null | Key  | Default | Extra |
+-|--||||-+
| GRANTEE        | varchar(81)  | YES  |      | NULL    |       |
| TABLE_CATALOG  | varchar(512) | YES  |      | NULL    |       |
| PRIVILEGE_TYPE | varchar(64)  | YES  |      | NULL    |       |
| IS_GRANTABLE   | varchar(3)   | YES  |      | NULL    |       |
+-|--||||-+
4 rows in set (0.00 sec)

VIEWS Table

VIEWS 表提供了关于 SQL 视图的信息。

mysql> create view test.v1 as select 1;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from views\G
*************************** 1. row ***************************
       TABLE_CATALOG: def
        TABLE_SCHEMA: test
          TABLE_NAME: v1
     VIEW_DEFINITION: select 1
        CHECK_OPTION: CASCADED
        IS_UPDATABLE: NO
             DEFINER: root@127.0.0.1
       SECURITY_TYPE: DEFINER
CHARACTER_SET_CLIENT: utf8
COLLATION_CONNECTION: utf8_general_ci
1 row in set (0.00 sec)

不支持的 Information Schema 表

TiDB 包含以下 INFORMATION_SCHEMA 表，但仅会返回空行：

COLUMN_PRIVILEGES
EVENTS
FILES
GLOBAL_STATUS
GLOBAL_VARIABLES
OPTIMIZER_TRACE
PARAMETERS
PARTITIONS
PLUGINS
PROFILING
REFERENTIAL_CONSTRAINTS
ROUTINES
SCHEMA_PRIVILEGES
SESSION_STATUS
TABLESPACES
TABLE_PRIVILEGES
TRIGGERS