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Views

TiDB 支持视图。视图充当虚拟表，其模式由创建该视图的 SELECT 语句定义。使用视图具有以下优点：

  • 仅向用户暴露安全的字段和数据，以确保底层表中敏感字段和数据的安全。
  • 定义经常出现的复杂查询作为视图，使复杂查询更简便、更方便。

查询视图

查询视图类似于查询普通表。然而，当 TiDB 查询视图时，实际上是查询与该视图关联的 SELECT 语句。

显示元数据

获取视图的元数据，可以选择以下任意方法。

使用 SHOW CREATE TABLE view_name 或 SHOW CREATE VIEW view_name 语句

用法示例：

show create view v;

此语句显示与该视图对应的 CREATE VIEW 语句，以及创建视图时的 character_set_client 和 collation_connection 系统变量的值。

+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| View | Create View                                                                                                                                                         | character_set_client | collation_connection |
+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| v    | CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`127.0.0.1` SQL SECURITY DEFINER VIEW `v` (`a`) AS SELECT `s`.`a` FROM `test`.`t` LEFT JOIN `test`.`s` ON `t`.`a`=`s`.`a` | utf8                 | utf8_general_ci      |
+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
1 row in set (0.00 sec)

查询 INFORMATION_SCHEMA.VIEWS 表

用法示例：

select * from information_schema.views;

通过查询此表，可以查看视图的相关元信息，例如 TABLE_CATALOG、TABLE_SCHEMA、TABLE_NAME、VIEW_DEFINITION、CHECK_OPTION、IS_UPDATABLE、DEFINER、SECURITY_TYPE、CHARACTER_SET_CLIENT 和 COLLATION_CONNECTION。

+---------------+--------------+------------+------------------------------------------------------------------------+--------------+--------------+----------------+---------------+----------------------+----------------------+
| TABLE_CATALOG | TABLE_SCHEMA | TABLE_NAME | VIEW_DEFINITION                                                        | CHECK_OPTION | IS_UPDATABLE | DEFINER        | SECURITY_TYPE | CHARACTER_SET_CLIENT | COLLATION_CONNECTION |
+---------------+--------------+------------+------------------------------------------------------------------------+--------------+--------------+----------------+---------------+----------------------+----------------------+
| def           | test         | v          | SELECT `s`.`a` FROM `test`.`t` LEFT JOIN `test`.`s` ON `t`.`a`=`s`.`a` | CASCADED     | NO           | root@127.0.0.1 | DEFINER       | utf8                 | utf8_general_ci      |
+---------------+--------------+------------+------------------------------------------------------------------------+--------------+--------------+----------------+---------------+----------------------+----------------------+
1 row in set (0.00 sec)

使用 HTTP API

用法示例：

curl http://127.0.0.1:10080/schema/test/v

通过访问 http://{TiDBIP}:10080/schema/{db}/{view}，你可以获取该视图的所有元数据。

{
 "id": 122,
 "name": {
  "O": "v",
  "L": "v"
 },
 "charset": "utf8",
 "collate": "utf8_general_ci",
 "cols": [
  {
   "id": 1,
   "name": {
    "O": "a",
    "L": "a"
   },
   "offset": 0,
   "origin_default": null,
   "default": null,
   "default_bit": null,
   "default_is_expr": false,
   "generated_expr_string": "",
   "generated_stored": false,
   "dependences": null,
   "type": {
    "Tp": 0,
    "Flag": 0,
    "Flen": 0,
    "Decimal": 0,
    "Charset": "",
    "Collate": "",
    "Elems": null
   },
   "state": 5,
   "comment": "",
   "hidden": false,
   "version": 0
  }
 ],
 "index_info": null,
 "fk_info": null,
 "state": 5,
 "pk_is_handle": false,
 "is_common_handle": false,
 "comment": "",
 "auto_inc_id": 0,
 "auto_id_cache": 0,
 "auto_rand_id": 0,
 "max_col_id": 1,
 "max_idx_id": 0,
 "update_timestamp": 416801600091455490,
 "ShardRowIDBits": 0,
 "max_shard_row_id_bits": 0,
 "auto_random_bits": 0,
 "pre_split_regions": 0,
 "partition": null,
 "compression": "",
 "view": {
  "view_algorithm": 0,
  "view_definer": {
   "Username": "root",
   "Hostname": "127.0.0.1",
   "CurrentUser": false,
   "AuthUsername": "root",
   "AuthHostname": "%"
  },
  "view_security": 0,
  "view_select": "SELECT `s`.`a` FROM `test`.`t` LEFT JOIN `test`.`s` ON `t`.`a`=`s`.`a`",
  "view_checkoption": 1,
  "view_cols": null
 },
 "sequence": null,
 "Lock": null,
 "version": 3,
 "tiflash_replica": null
}

示例

以下示例创建一个视图，查询该视图，并删除该视图：

create table t(a int, b int);
Query OK, 0 rows affected (0.01 sec)
insert into t values(1, 1),(2,2),(3,3);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0
create table s(a int);
Query OK, 0 rows affected (0.01 sec)
insert into s values(2),(3);
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0
create view v as select s.a from t left join s on t.a = s.a;
Query OK, 0 rows affected (0.01 sec)
select * from v;
+------+
| a    |
+------+
| NULL |
|    2 |
|    3 |
+------+
3 rows in set (0.00 sec)
drop view v;
Query OK, 0 rows affected (0.02 sec)

限制

目前，TiDB 中的视图受到以下限制：

  • 目前尚不支持物化视图。
  • TiDB 中的视图为只读，不支持 UPDATE、INSERT、DELETE 和 TRUNCATE 等写操作。
  • 对于已创建的视图，唯一支持的 DDL 操作是 DROP [VIEW | TABLE]

相关链接