But we can also make more complicated filtering, for example, by two columns. Let's see the syntax of such filtering.

```sql
SELECT column1, AGG_FUNCTION(column_2) AS name2, 
AGG_FUNCTION(column_3) AS name3
FROM table
GROUP BY column1
HAVING condition for name2, condition for name3
```

It will be easier to understand it in practice!

In this section, you will learn how to group and work with such data. For this, we will get acquainted with such an operator as GROUP BY. You will also learn how to filter grouped data using the operator HAVING.

In this section, you will learn what nested subqueries are, how to create them, and how to work with them.

In this section, you will learn how you can combine several tables, thus working with one common table, which will simplify the creation of queries.

In this section, you will learn how to combine several tables in different ways, in particular: INNER JOIN, LEFT JOIN, RIGHT JOIN.

relation_id	line_name	station_name	time_to_next_station
1	Green	Angrignon	10
2	Green	Monk	16
3	Green	Verdun	9
...	...	...	...
21	Yellow	Longueuil	10

Intermediate SQL

More Complex Filtering

Task