SQL Syntax Rules: How to Write Readable SQL Statements

Every language has grammar. SQL's grammar is small and forgiving, but a few rules cause most beginner errors. This lesson covers them, along with a simple style that keeps your queries easy to read.

Statements and clauses#

A statement is one complete instruction to the database. A statement is made of clauses, each starting with a keyword:

SELECT name, salary       -- SELECT clause: which columns
FROM employees            -- FROM clause: which table
WHERE salary > 60000      -- WHERE clause: which rows
ORDER BY salary DESC;     -- ORDER BY clause: in what order

Clauses must appear in a fixed order. You can leave optional ones out, but you cannot reorder them. WHERE before FROM is a syntax error.

The usual order of clauses in a SELECT statement is:

SELECT ...
FROM ...
JOIN ... ON ...
WHERE ...
GROUP BY ...
HAVING ...
ORDER BY ...
LIMIT ...;

Semicolons end statements#

A semicolon ; marks the end of a statement. It is required when you run several statements together:

SELECT name FROM customers;
SELECT order_id FROM orders;

Many tools let you run a single statement without one, but adding it every time is a good habit.

Keywords are not case-sensitive#

SELECT, select and Select all work. The common convention is UPPERCASE keywords and lowercase names, so the structure of a query stands out:

-- All of these are the same query
select name from employees;
SELECT name FROM employees;
SeLeCt name FrOm employees;

Whitespace and line breaks do not matter#

SQL ignores extra spaces, tabs and new lines. These two queries are identical to the database:

SELECT name, salary FROM employees WHERE department = 'Sales' ORDER BY salary DESC;

SELECT name, salary
FROM employees
WHERE department = 'Sales'
ORDER BY salary DESC;

The second is much easier for people to read. Put each major clause on its own line.

Quotes: single for text, double for names#

This is the rule that trips up beginners most often:

To put a single quote inside text, write it twice:

SELECT 'Priya''s team' AS label;

label
------------
Priya's team

Comments#

Comments are notes for humans; the database ignores them.

-- A single-line comment starts with two dashes
SELECT name, salary
FROM employees
/* A block comment
   can span several lines */
WHERE salary > 60000;

Use comments to explain why a query does something unusual, not to repeat what the SQL already says.

Reserved words as names#

Words like order, group, select and user are reserved keywords. Naming a table order forces you to quote it every time ("order" or `order`). Prefer plural or more specific names such as orders or user_accounts.

A simple style guide#

These habits make SQL easier to read and review:

1. Keywords in UPPERCASE, names in lowercase snake_case (hire_date).
2. One major clause per line.
3. Indent continuation lines, such as extra AND conditions.
4. Name things clearly: orders, not tbl1.
5. List columns explicitly instead of SELECT * in finished queries.

SELECT e.name,
       e.department,
       e.salary
FROM employees AS e
WHERE e.department = 'Engineering'
  AND e.salary > 75000
ORDER BY e.salary DESC;

Common mistakes#

Practice#

select name, city,
from employees
order by name
where city = "Mumbai"

SELECT name, city
FROM employees
WHERE city = 'Mumbai'
ORDER BY name;

name | city
-----+-------
Asha | Mumbai
John | Mumbai

Key takeaway#