Naming things so they read

01 / 04

The heading comes out as the expression

The result of an aggregation takes whatever you wrote as its heading. Look at the first line below.

A heading of SUM(quantity) makes sense to whoever wrote it, but it reads badly to someone handed the result later on.

SELECT SUM(quantity) FROM orders;

Result

SUM(quantity)
27

02 / 04

Add AS name behind a column or an expression and the heading changes to that name. This is called an alias.

Nothing about the calculation changes. Only the heading does.

SELECT SUM(quantity) AS total  FROM orders;

Result

total
27

03 / 04

A calculation between columns can be named just as well. The longer the expression, the more a name earns its keep.

Below works out "10 points for each one" and calls it points.

SELECT id, quantity * 10 AS points  FROM orders  WHERE id = 3;

Result

id | points
3 | 40

04 / 04

ORDER BY takes an alias directly. That saves writing a long expression twice, which pays off when you put aggregating and sorting together.

Let us write some. Aliases will keep coming to your rescue once you start joining, as well.

SELECT channel,  SUM(quantity) AS total  FROM orders  GROUP BY channel  ORDER BY total DESC;

Result

channel | total
shop | 10
web | 9
app | 8