From cf9d5132a8ed32249a0255e1565c901974c29f2e Mon Sep 17 00:00:00 2001 From: HuaiyuXu <391585975@qq.com> Date: Mon, 25 May 2020 19:49:37 +0800 Subject: [PATCH] cherry pick #3179 to release-3.0 Signed-off-by: ti-srebot --- views.md | 140 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 138 insertions(+), 2 deletions(-) diff --git a/views.md b/views.md index 6c084a9bc6dd..cc3431432686 100644 --- a/views.md +++ b/views.md @@ -12,7 +12,143 @@ TiDB 支持视图，视图是一张虚拟表，该虚拟表的结构由创建视 查询一个视图和查询一张普通表类似。但是 TiDB 在真正执行查询视图时，会将视图展开成创建视图时定义的 `SELECT` 语句，进而执行展开后的查询语句。 -## 样例 +## 查看视图的相关信息 + +通过以下方式，可以查看 view 相关的信息。 + +### 使用 `SHOW CREATE TABLE view_name` 或 `SHOW CREATE VIEW view_name` 语句 + +示例： + +{{< copyable "sql" >}} + +```sql +show create view v; +``` + +使用该语句可以查看 view 对应的创建语句，及创建 view 时对应的 `character_set_client` 及 `collation_connection` 系统变量值。 + +```sql ++------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ +| 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 + +示例: + +{{< copyable "sql" >}} + +```sql +select * from information_schema.views; +``` + +通过查询该表可以查看 view 的相关元信息，如 `TABLE_CATALOG`、`TABLE_SCHEMA`、`TABLE_NAME`、`VIEW_DEFINITION`、`CHECK_OPTION`、`IS_UPDATABLE`、`DEFINER`、`SECURITY_TYPE`、`CHARACTER_SET_CLIENT`、`COLLATION_CONNECTION` 等。 + +```sql ++---------------+--------------+------------+------------------------------------------------------------------------+--------------+--------------+----------------+---------------+----------------------+----------------------+ +| 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) +``` + +### 查询 HTTP API + +示例: + +{{< copyable "" >}} + +``` +curl http://127.0.0.1:10080/schema/test/v +``` + +通过访问 `http://{TiDBIP}:10080/schema/{db}/{view}` 可以得到对应 view 的所有元信息。 + +``` +{ + "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 以下例子将创建一个视图，并在该视图上进行查询，最后删除该视图。 @@ -100,7 +236,7 @@ Query OK, 0 rows affected (0.02 sec) 目前 TiDB 中的视图有以下局限性： - 不支持物化视图。 -- TiDB 中视图为只读视图，不支持对视图进行 `UPDATE`、`INSERT`、`DELETE` 等写入操作。 +- TiDB 中视图为只读视图，不支持对视图进行 `UPDATE`、`INSERT`、`DELETE`、`TRUNCATE` 等写入操作。 - 对已创建的视图仅支持 `DROP` 的 DDL 操作，即 `DROP [VIEW | TABLE]`。 ## 扩展阅读