You can also add a view using Create View in the View menu and see the results in the Views tab just like a table.

Exercise

1. Write a query that returns the number of articles published in each journal on each month, sorted from most popular journal to the ones with least publications each month starting from the most recent records. Save this query as a VIEW.

Overview

Teaching: 30 min 
Exercises: 30 min

Questions

• Linking tables together and using shorthand

Objectives

• to understand how to link tables together

Joins

To combine data from two tables we use the SQL JOIN command, which comes after the FROM command.

We also need to tell the computer which columns provide the link between the two tables using the word ON. What we want is to join the data with the same journal name.

SELECT *
FROM articles
JOIN journals
ON articles.issns = journals.issns;

ON is like WHERE, it filters things out according to a test condition. We use the table.colname format to tell the manager what column in which table we are referring to.

Alternatively, we can use the word USING, as a short-hand. In this case we are telling the manager that we want to combine articles with journals and that the common column is issns.

SELECT *
FROM articles
JOIN journals
USING (issns);

We often won’t want all of the fields from both tables, so anywhere we would have used a field name in a non-join query, we can use table.colname.

For example, what if we wanted information on published articles in different journals, but instead of their ISSN we wanted the actual journal title.

SELECT articles.issns, journal_title, title, first_author, citation_count, author_count, month, year
FROM articles
JOIN journals
ON articles.issns = journals.issns;

Joins can be combined with sorting, filtering, and aggregation. So, if we wanted average number of authors for articles on different journals, we could do something like

SELECT articles.issns, journal_title, ROUND(AVG(author_count), 2)
FROM articles
JOIN journals
ON articles.issns = journals.issns;
GROUP BY articles.issns;

Challenge: 

It is worth mentioning that you can join multiple tables. For example:

SELECT title, first_author, journal_title, language FROM articles JOIN journals ON articles.issns = journals.issns JOIN languages ON languages.id = articles.languageid

Challenge: 

Aliases

As queries get more complex names can get long and unwieldy. To help make things clearer we can use aliases to assign new names to things in the query.

We can alias both table names:

SELECT ar.title, ar.first_author, jo.journal_title
FROM articles AS ar
JOIN journals  AS jo
ON ar.issns = jo.issns;

And column names:

SELECT ar.title AS title, ar.first_author AS author, jo.journal_title AS journal
FROM articles AS ar
JOIN journals  AS jo
ON ar.issns = jo.issns;

The AS isn’t technically required, so you could do

SELECT a.title t
FROM articles a;

but using AS is much clearer so it is good style to include it.

Extra Challenges (optional)

SQL queries help us ask specific questions which we want to answer about our data. The real skill with SQL is to know how to translate our scientific questions into a sensible SQL query (and subsequently visualize and interpret our results).

Have a look at the following questions; these questions are written in plain English. Can you translate them to SQL queries and give a suitable answer?

Challenge 1 

How many plots from each type are there?

Solution 1 

Challenge 2 

How many papers have a single author? How many have 2 authors? How many 3? etc?

Solution 2 

Challenge 3 

How many articles are published for each language? (Ignore articles where language is unknown).

Solution 3 

Challenge 4 

How many articles are published for each licence type, and what is the average number of citations for that licence type

Solution 4 

Challenge 5 

Create a view with article, journal and publisher information