Saving queries

Overview

Teaching: 20 min
Exercises: 10 min

Questions

• How can I save a query for future use?

• How can I remove a saved query?

Objectives

• Learn how to save repeated queries as ‘Views’ and how to drop them.

Saving queries for future use

It is not uncommon to repeat the same operation more than once, for example for monitoring or reporting purposes. SQL comes with a very powerful mechanism to do this: views. Views are queries saved in the database. You query it as a (virtual) table that is populated every time you query it.

Creating a view from a query requires you to add CREATE VIEW viewname AS before the query itself. For example, if we want to save the query giving the number of journals in a view, we can write:

CREATE VIEW journal_counts AS
SELECT ISSNs, COUNT(*)
FROM articles
GROUP BY ISSNs;

Now, we will be able to access these results with a much shorter notation:

SELECT *
FROM journal_counts;

Assuming we do not need this view anymore, we can remove it from the database almost as we would a table:

DROP VIEW journal_counts;

In DBBrowser for SQLite, you can also create a view from any query by omitting the CREATE VIEW viewname AS statement and instead, clicking the small Save icon at the bottom of the Execute SQL tab and then clicking Save as view. Whatever method you use to create a view, it will appear in the list of views under the Database Structure tab.

Challenge

Write a CREATE VIEW query that JOINS the articles table with the journals table on ISSNs and returns the COUNT of article records grouped by the Journal_Title in DESC order.

Solution

CREATE VIEW journal_counts AS
SELECT journals.Journal_Title, COUNT(*)
FROM articles
JOIN journals
ON articles.ISSNs = journals.ISSNs
GROUP BY Journal_Title
ORDER BY COUNT(*) DESC

Key Points

• Saving queries as ‘Views’ allows you to save time and avoid repeating the same operation more than once.