SQL SELECT

The SELECT statement reads data from a table. It is the command you will use most.

SELECT Syntax

SELECT column1, column2
FROM table_name;

You list the columns you want after SELECT, and the table after FROM. The answer comes back as a new table, called the result set.

Select Some Columns

This query returns only the name and the city of each student:

SELECT name, city
FROM students;

The columns come back in the order you wrote them, not the order in the table.

Select All Columns

Use * to get every column:

SELECT * FROM courses;

SELECT DISTINCT

A column often has the same value many times. DISTINCT returns each value only once:

SELECT DISTINCT city
FROM students;

Six students live in only three different cities. You can also count the different values:

SELECT COUNT(DISTINCT city)
FROM students;

Rename a Column with AS

An alias gives a column a new name in the result. It does not change the table itself.

SELECT name AS student_name, marks AS score
FROM students;

Calculations in SELECT

You can calculate a new value for every row. Here every student gets 5 bonus marks, only in the result:

SELECT name, marks + 5 AS new_marks
FROM students;

You can use +, -, * and / in this way.

Summary

Exercise