**JOIN** operator makes combining the records into two tables based on the related column between them. For example, we want to join `singers` and `songs` columns in some way. These tables have the same column: `singer_id` in songs and `id` in singers. We join them by this column, and now records are rearranged into groups by this `id`.

`JOIN` can be applied for multiple tables, and the syntax is:

--do not run this query
SELECT columns
FROM table1 INNER JOIN table2
ON table1.col1 = table2.col2
WHERE conditions
GROUP BY columns
HAVING agg_condition
ORDER BY columns

`JOIN` is an alternative to nested queries. Let's look at the following example, find all songs released between 1970 and 1990:

SELECT songs.title
FROM albums INNER JOIN songs ON songs.album_id = albums.id
WHERE year>=1970 AND year<=1990

This diagram shows how INNER JOIN works. Chosen columns `albums_id` and `id` are joined, and only `id`s present in both columns appear in the result query. Intersection of sets (1, 2, 3) and (1, 2, 4, 2) is a (1, 2, 2).

This way, we avoid using nested queries. Using `Joins` is a common practice, and in the next chapters, we'll learn other types, except `INNER JOIN`.

If you're an expert in creating queries for a single table, improve your knowledge! Let's start accessing and manipulating two and more tables. During the course, you'll learn how to work with special statements, what is the join and how to use it, and also will practice a lot!

We shall take a look at the database we'll work with and how we can create a query inside another query.

Learn how to join and work with multiple tables.

Try creating queries with no limits on how you should do that. Use all your knowledge from previous chapters!

SQL Inner Join

Lösning