DataCamp

Inner join (3)

The ability to combine multiple joins in a single query is a powerful feature of SQL. Check out how this is done with the left_table, the right_table, and the table1 from the diagrams in the slides. (table1 is introduced in Chapter 2 and is seen below.)

+-----+
| id  |
|-----|
|   1 |
|   2 |
|   3 |
+-----+

SELECT *
FROM left_table
INNER JOIN right_table
ON left_table.id = right_table.id
INNER JOIN table1
ON left_table.id = table1.id;

As you can see here it becomes tedious to continually write long table names in joins. This is when it becomes useful to alias each table using the first letter of its name (e.g. countries AS c)! It is standard practice to alias in this way and, if you choose to alias tables or are asked to specifically for an exercise in this course, you should follow this protocol.

Now, for each country, you want to get the country name, its region, and the fertility rate and unemployment rate for both 2010 and 2015.

Create an inner join with countries on the left and populations on the right.
Alias countries AS c and populations AS p.
Select country code from countries, name, region, year, and fertility rate. (This corresponds to selecting five fields in total.)

Take Hint (-9 XP)

Exercise

Inner join (3)

Instructions 1/3