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Views

TiDB supports views. A view acts as a virtual table, whose schema is defined by the SELECT statement that creates the view. Using views has the following benefits:

  • Exposing only safe fields and data to users to ensure security of sensitive fields and data stored in the underlying table.
  • Defining complex queries that frequently appear as views to make complex queries easier and more convenient.

Query views

Querying a view is similar to querying an ordinary table. However, when TiDB queries a view, it actually queries the SELECT statement associated with the view.

Show metadata

To obtain the metadata of views, choose any of the following methods.

Use the SHOW CREATE TABLE view_name or SHOW CREATE VIEW view_name statement

Usage example:

show create view v;

This statement shows the CREATE VIEW statement corresponding to this view and the value of the character_set_client and collation_connection system variables when the view was created.

+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ | 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)

Query the INFORMATION_SCHEMA.VIEWS table

Usage example:

select * from information_schema.views;

You can view the relevant meta information of the view by querying this table, such as TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME, VIEW_DEFINITION, CHECK_OPTION, IS_UPDATABLE, DEFINER, SECURITY_TYPE, CHARACTER_SET_CLIENT, and 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)

Use the HTTP APIs

Usage example:

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

By visiting http://{TiDBIP}:10080/schema/{db}/{view}, you can get all the metadata for the view.

{ "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 }

Example

The following example creates a view, queries this view, and delete this view:

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)

Limitations

Currently, views in TiDB are subject to the following limitations:

  • Materialized views are not supported yet.
  • Views in TiDB are read-only and do not support write operations such as UPDATE, INSERT, DELETE, and TRUNCATE.
  • For created views, the only supported DDL operation is DROP [VIEW | TABLE]

See also

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