SQLite - VIEWS
A view is nothing more than a SQLite statement that is stored in the database with an associated name. A view is actually a composition of a table in the form of a predefined SQLite query.
A view can contain all rows of a table or selected rows from one or more tables. A view can be created from one or many tables which depends on the written SQLite query to create a view.
Views which are kind of virtual tables, allow users to do the following:
Structure data in a way that users or classes of users find natural or intuitive.
Restrict access to the data such that a user can only see limited data instead of complete table.
Summarize data from various tables which can be used to generate reports.
SQLite views are read-only and so you may not execute a DELETE, INSERT or UPDATE statement on a view. But you can create a trigger on a view that fires on an attempt to DELETE, INSERT, or UPDATE a view and do what you need in the body of the trigger.
The SQLite views are created using the CREATE VIEW statement. The SQLIte views can be created from a single table, multiple tables, or another view.
The basic CREATE VIEW syntax is as follows:
CREATE [TEMP | TEMPORARY] VIEW view_name AS SELECT column1, column2..... FROM table_name WHERE [condition];
You can include multiple tables in your SELECT statement in very similar way as you use them in normal SQL SELECT query. If the optional TEMP or TEMPORARY keyword is present, the view will be created in the temp database.
Consider COMPANY table is having the following records:
ID NAME AGE ADDRESS SALARY ---------- ---------- ---------- ---------- ---------- 1 Paul 32 California 20000.0 2 Allen 25 Texas 15000.0 3 Teddy 23 Norway 20000.0 4 Mark 25 Rich-Mond 65000.0 5 David 27 Texas 85000.0 6 Kim 22 South-Hall 45000.0 7 James 24 Houston 10000.0
Now, following is an example to create a view from COMPANY table. This view would be used to have only few columns from COMPANY table:
sqlite> CREATE VIEW COMPANY_VIEW AS SELECT ID, NAME, AGE FROM COMPANY;
Now, you can query COMPANY_VIEW in similar way as you query an actual table. Following is the example:
sqlite> SELECT * FROM COMPANY_VIEW;
This would produce the following result:
ID NAME AGE ---------- ---------- ---------- 1 Paul 32 2 Allen 25 3 Teddy 23 4 Mark 25 5 David 27 6 Kim 22 7 James 24
To drop a view, simply use the DROP VIEW statement with the view_name. The basic DROP VIEW syntax is as follows:
sqlite> DROP VIEW view_name;
Following command will delete COMPANY_VIEW view, which we created in the last section:
sqlite> DROP VIEW COMPANY_VIEW;