Your first SELECT

SELECT is the most used command in SQL. It reads data from the database and never changes it.

The pattern

SELECT columns FROM table;

• SELECT — what you want to see (columns);
• FROM — where it comes from (table);
• ; — the command ends here.

All columns: *

The asterisk means “every column”. Handy for a quick look at what a table holds:

SELECT * FROM faculties;

In real projects, be careful with SELECT *: if a column is added to the table later, the result changes, and data you do not need gets loaded too. Naming the columns you need is a good habit.

Only the columns you need

Columns are separated by commas and come out in exactly the order you wrote them:

SELECT last_name, first_name, course FROM students;

Case and spacing

SQL keywords can be written in any case: SELECT, select, Select — all the same. They are usually written in capitals so the query is easier to read.

A long query can be split over several lines — the database treats everything up to ; as one command:

SELECT first_name,
       last_name,
       city
FROM students;

Renaming a column: AS

You can change the heading of a column in the result. This is called an alias:

SELECT first_name AS name, last_name AS surname FROM students LIMIT 5;

If an alias contains a space or special characters, put it in quotes:

In PostgreSQL use double quotes: AS "Student name". Single quotes ('…') are only for text values.

A calculated column

SELECT can contain expressions, not just columns. For example, teachers’ yearly salary:

SELECT first_name, last_name, salary * 12 AS yearly FROM teachers;

Remember

• SELECT columns FROM table; is the basic pattern for reading data.
• * means every column, but at work it is better to name the ones you need.
• AS gives a column of the result a new name.