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Views

This document describes how to use views in TiDB.

Overview

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

  • You can create views to expose only safe fields and data to users, which ensures the security of sensitive fields and data in the underlying tables.
  • You can create views for complex queries that are frequently used to make complex queries easier and more convenient.

Create a view

In TiDB, a complex query can be defined as a view with the CREATE VIEW statement. The syntax is as follows:

CREATE VIEW view_name AS query;

Note that you cannot create a view with the same name as an existing view or table.

For example, the multi-table join query gets a list of books with average ratings by joining the books table and the ratings table through a JOIN statement.

For the convenience of subsequent queries, you can define the query as a view using the following statement:

CREATE VIEW book_with_ratings AS
SELECT b.id AS book_id, ANY_VALUE(b.title) AS book_title, AVG(r.score) AS average_score
FROM books b
LEFT JOIN ratings r ON b.id = r.book_id
GROUP BY b.id;

Query views

Once a view is created, you can use the SELECT statement to query the view just like a normal table.

SELECT * FROM book_with_ratings LIMIT 10;

When TiDB queries a view, it queries the SELECT statement associated with the view.

Update views

Currently, the view in TiDB does not support the ALTER VIEW view_name AS query;, you can "update" a view in the following two ways:

  • Delete the old view with the DROP VIEW view_name; statement, and then update the view by creating a new view with the CREATE VIEW view_name AS query; statement.
  • Use the CREATE OR REPLACE VIEW view_name AS query; statement to overwrite an existing view with the same name.
CREATE OR REPLACE VIEW book_with_ratings AS
SELECT b.id AS book_id, ANY_VALUE(b.title), ANY_VALUE(b.published_at) AS book_title, AVG(r.score) AS average_score
FROM books b
LEFT JOIN ratings r ON b.id = r.book_id
GROUP BY b.id;

Using the SHOW CREATE TABLE|VIEW view_name statement

SHOW CREATE VIEW book_with_ratings\G

The result is as follows:

*************************** 1. row ***************************
                View: book_with_ratings
         Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`%` SQL SECURITY DEFINER VIEW `book_with_ratings` (`book_id`, `ANY_VALUE(b.title)`, `book_title`, `average_score`) AS SELECT `b`.`id` AS `book_id`,ANY_VALUE(`b`.`title`) AS `ANY_VALUE(b.title)`,ANY_VALUE(`b`.`published_at`) AS `book_title`,AVG(`r`.`score`) AS `average_score` FROM `bookshop`.`books` AS `b` LEFT JOIN `bookshop`.`ratings` AS `r` ON `b`.`id`=`r`.`book_id` GROUP BY `b`.`id`
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
1 row in set (0.00 sec)

Query the INFORMATION_SCHEMA.VIEWS table

SELECT * FROM information_schema.views WHERE TABLE_NAME = 'book_with_ratings'\G

The result is as follows:

*************************** 1. row ***************************
       TABLE_CATALOG: def
        TABLE_SCHEMA: bookshop
          TABLE_NAME: book_with_ratings
     VIEW_DEFINITION: SELECT `b`.`id` AS `book_id`,ANY_VALUE(`b`.`title`) AS `ANY_VALUE(b.title)`,ANY_VALUE(`b`.`published_at`) AS `book_title`,AVG(`r`.`score`) AS `average_score` FROM `bookshop`.`books` AS `b` LEFT JOIN `bookshop`.`ratings` AS `r` ON `b`.`id`=`r`.`book_id` GROUP BY `b`.`id`
        CHECK_OPTION: CASCADED
        IS_UPDATABLE: NO
             DEFINER: root@%
       SECURITY_TYPE: DEFINER
CHARACTER_SET_CLIENT: utf8mb4
COLLATION_CONNECTION: utf8mb4_general_ci
1 row in set (0.00 sec)

Drop views

Use the DROP VIEW view_name; statement to drop a view.

DROP VIEW book_with_ratings;

Limitation

For limitations of views in TiDB, see Limitations of Views.

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