SQL SELECT: read data from a table

SELECT is the first statement everyone learns in SQL, and the one you will write most often. It is used to read data: show the content of a table, pick a few columns, compute new values. It never changes the database, so you can try it without any risk.

In this lesson, you will see how to write a SELECT query, how to choose the columns to display, and why the famous SELECT * is handy… but not always a good idea.

Syntax

SELECT column1, column2, …
FROM table_name;

How it works

A SELECT query reads almost like a sentence: “select these columns from this table”.

• SELECT lists the columns to display, separated by commas. They appear in the order you write them.
• FROM names the table that holds these columns.
• The star * means “all columns”. SELECT * FROM produits therefore shows the whole table.
• The semicolon ; ends the query. It is required when you chain several queries.

SQL keywords are not case-sensitive: select and SELECT work the same way. The convention is to write keywords in upper case and table and column names in lower case, so the query is easy to read.

Why avoid SELECT * in an application?

SELECT * is perfect for exploring a table. In a real application, you usually list the columns you need: the query transfers less data, and it does not break if someone adds or reorders columns in the table.

Diagram

Simplified diagram to show the idea. The examples below use the real SQL Quest practice database (a fictional online shop: see the full schema).

Examples with their results

SELECT * FROM fournisseurs;

SELECT nom, prix FROM produits;

SELECT ville, nom, prenom FROM clients;

Common mistakes

SELECT prenom nom FROM clients;

SELECT prenom, nom FROM clients;

SELECT prenom, nom, FROM clients;

SELECT prenom, nom FROM clients;

SELECT * FROM client;

SELECT * FROM clients;

Exercises

Try writing the query yourself before opening the solution.

SELECT email, ville FROM clients;

SELECT nom, poste, salaire FROM employes;

Frequently asked questions