SQL Syntax

SQL has a few simple writing rules. Learn them once and every later lesson will be easier to read.

SQL Statements

A command you send to the database is called a statement. Most actions in a database are done with statements.

SELECT * FROM students;

This statement reads every column of every row from the students table.

A statement is made of:

• Keywords, words with a special meaning such as SELECT, FROM and WHERE
• Names of tables and columns, such as students and city
• Values, such as 'Karachi' or 20

Keywords Are Not Case Sensitive

SELECT, select and Select all mean the same thing. These two statements give the same result:

SELECT name FROM students;
select name from students;

Semicolon at the End

The semicolon ; marks the end of a statement. It lets you send several statements one after another:

SELECT name FROM students;
SELECT title FROM courses;

Some tools run a single statement without a semicolon, but always adding it is a good habit.

Spaces and New Lines

SQL does not care about extra spaces or line breaks. A long query is easier to read when each part is on its own line:

SELECT name, city, marks
FROM students
WHERE marks > 80;

Text Values and Numbers

Text values go inside single quotes. Numbers are written without quotes.

SELECT name FROM students WHERE city = 'Lahore';
SELECT name FROM students WHERE age = 22;

If a text value itself has a single quote in it, write two single quotes: 'Ali''s laptop'.

Comments

Comments are notes for people. The database ignores them.

-- This is a one-line comment
SELECT name FROM students; -- a comment can also end a line

/* This is a comment
   over several lines */
SELECT title FROM courses;

The Most Important SQL Commands

You will learn each of these in the following lessons.

Exercise