20.29. The `INFORMATION_SCHEMA VIEWS` Table

The VIEWS table provides information about views in databases. You must have the SHOW VIEW privilege to access this table.

`INFORMATION_SCHEMA` Name	`SHOW` Name	Remarks
`TABLE_CATALOG`		`def`
`TABLE_SCHEMA`
`TABLE_NAME`
`VIEW_DEFINITION`
`CHECK_OPTION`
`IS_UPDATABLE`
`DEFINER`
`SECURITY_TYPE`
`CHARACTER_SET_CLIENT`		MySQL extension
`COLLATION_CONNECTION`		MySQL extension

Notes:

The VIEW_DEFINITION column has most of what you see in the Create Table field that SHOW CREATE VIEW produces. Skip the words before SELECT and skip the words WITH CHECK OPTION. Suppose that the original statement was:
```
CREATE VIEW v AS  SELECT s2,s1 FROM t  WHERE s1 > 5  ORDER BY s1  WITH CHECK OPTION;
```
Then the view definition looks like this:
```
SELECT s2,s1 FROM t WHERE s1 > 5 ORDER BY s1
```
The CHECK_OPTION column has a value of NONE, CASCADE, or LOCAL.
MySQL sets a flag, called the view updatability flag, at CREATE VIEW time. The flag is set to YES (true) if UPDATE and DELETE (and similar operations) are legal for the view. Otherwise, the flag is set to NO (false). The IS_UPDATABLE column in the VIEWS table displays the status of this flag. It means that the server always knows whether a view is updatable. If the view is not updatable, statements such UPDATE, DELETE, and INSERT are illegal and will be rejected. (Note that even if a view is updatable, it might not be possible to insert into it; for details, refer to Section 13.1.20, "CREATE VIEW Syntax".)
DEFINER: The account of the user who created the view, in 'user_name'@'host_name' format. SECURITY_TYPE has a value of DEFINER or INVOKER.
CHARACTER_SET_CLIENT: The session value of the character_set_client system variable when the view was created.
COLLATION_CONNECTION: The session value of the collation_connection system variable when the view was created.

MySQL lets you use different sql_mode settings to tell the server the type of SQL syntax to support. For example, you might use the ANSI SQL mode to ensure MySQL correctly interprets the standard SQL concatenation operator, the double bar (||), in your queries. If you then create a view that concatenates items, you might worry that changing the sql_mode setting to a value different from ANSI could cause the view to become invalid. But this is not the case. No matter how you write out a view definition, MySQL always stores it the same way, in a canonical form. Here is an example that shows how the server changes a double bar concatenation operator to a CONCAT() function:

mysql> SET sql_mode = 'ANSI';Query OK, 0 rows affected (0.00 sec)mysql> CREATE VIEW test.v AS SELECT 'a' || 'b' as col1;Query OK, 0 rows affected (0.00 sec)mysql> SELECT VIEW_DEFINITION FROM
        INFORMATION_SCHEMA.VIEWS    -> WHERE TABLE_SCHEMA = 'test'
        AND TABLE_NAME = 'v';+----------------------------------+| VIEW_DEFINITION                  |+----------------------------------+| select concat('a','b') AS `col1` |+----------------------------------+1 row in set (0.00 sec)

The advantage of storing a view definition in canonical form is that changes made later to the value of sql_mode will not affect the results from the view. However an additional consequence is that comments prior to SELECT are stripped from the definition by the server.

20.29. The INFORMATION_SCHEMA VIEWS Table

20.29. The `INFORMATION_SCHEMA VIEWS` Table