The view of mysql is an interface for storing data in the mysql database, which can also be said to be a virtual table; these data can be data from one or several basic tables or views, or user-defined data. ; When the data in the basic table changes, the data in the view changes accordingly.
The operating environment of this article: Windows 7 system, mysql version 5.0, Dell G3 computer.
What is the view of mysql?
mysql View
View is an interface for storing data in the mysql database
Introduction
View is an interface for storing data, which can also be said to be a virtual table. This data can be data from one or several basic tables (or views). It can also be user-defined data. In fact, the data is not stored in the view. The data is still stored in the basic table. When the data in the basic table changes, the data in the view changes accordingly.
Function
1. Mysql view makes the query very clear. The data stored in the view is the data we want, and it can simplify user operations.
2, mysql view makes data more secure. The data in the view does not exist in the view, but is still in the basic table. Through the relationship of the view, we can effectively protect our important data
Type
Mysql views have three types: MERGE, TEMPTABLE, UNDEFINED. If there is no ALGORITHM clause, the default algorithm is UNDEFINED. Algorithms affect how MySQL handles views.
1, MERGE, will merge the text of the statement that references the view with the view definition, so that a certain part of the view definition replaces the corresponding part of the statement.
2, TEMPTABLE, the results of the view will be placed in a temporary table, and then used to execute the statement.
3, UNDEFINED, MySQL will choose the algorithm to be used. If possible, it favors MERGE over TEMPTABLE because MERGE is generally more efficient and the view is not updatable if temporary tables are used.
Grammar
CREATE [OR REPLACE] [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]
VIEW view_name [(column_list)]
AS select_statement
[WITH [CASCADED | LOCAL] CHECK OPTION]
This statement can create a new view. If the OR REPLACE clause is given, this statement can also Replace existing view. select_statement is a SELECT statement that gives the definition of a view. This statement can select from a base table or other view.
This statement requires CREATE VIEW permission on the view, as well as certain permissions on each column selected by the SELECT statement. SELECT permission is required for columns used elsewhere in the SELECT statement. If there is an OR REPLACE clause, you must have DROP permission on the view.
Views belong to the database. By default, a new view will be created in the current database. To explicitly create a view in a given database, when creating it, specify the name as db_name.view_name.
mysql> CREATE VIEW test.v AS SELECT * FROM t;
Tables and views share the same namespace in the database, therefore, the database cannot contain tables and views with the same name.
Views must have unique column names without duplication, just like the base table. By default, the column names retrieved by the SELECT statement are used as view column names. To define explicit names for view columns, use the optional column_list clause, which lists IDs separated by commas. The number of names in column_list must equal the number of columns retrieved by the SELECT statement.
The columns retrieved by the SELECT statement can be simple references to table columns. It can also be an expression using functions, constant values, operators, etc.
Unqualified tables or views in the SELECT statement will be interpreted according to the default database. A view can reference a table or view in another database by qualifying the table or view name with the appropriate database name.
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