SQL Syntax and Comments

SQL has a small set of syntax rules, and once you know them you can read almost any query. This lesson covers how a statement is built, when case matters, how to quote text and names, and how to write comments, with every rule shown on a real MySQL 8.4 query.

Anatomy of a SQL statement

SELECT first_name, salaryFROM employeesWHERE dept_id = 2;

Rule 1: keywords are not case sensitive

SELECT, select and SeLeCt all work. Writing keywords in UPPER CASE and names in lower case is the usual style because it makes queries easier to scan:

select first_name from employees where emp_id = 101;

Text comparisons are also case insensitive by default in MySQL, because the default collation (utf8mb4_0900_ai_ci) ends in ci, meaning case-insensitive:

SELECT first_name FROM employees WHERE city = 'PUNE';

Rule 2: whitespace and line breaks do not matter

You may put a whole query on one line or spread it over many. Spread long queries one clause per line, so they are easy to read and to compare in code reviews:

SELECT   first_name,         job_titleFROM     employeesWHERE    salary >= 100000;

Rule 3: end statements with a semicolon

The semicolon separates statements. In the mysql client a statement does not run until you type ;. When you send several statements at once, each needs one:

SELECT COUNT(*) AS departments FROM departments;SELECT COUNT(*) AS customers FROM customers;

Rule 4: quotes

To put a single quote inside text, double it:

SELECT 'It''s a test' AS message, 'O''Brien' AS surname;

Names normally need no quotes. Backticks are only needed when a name is a reserved word or contains spaces or special characters:

SELECT dept_name AS `Department Name`, location AS `where`FROM departmentsWHERE dept_id <= 2;

Rule 5: numbers, text and NULL

SELECT 42 AS whole_number, 3.75 AS decimal_number, 'hello' AS text_value, '2026-01-31' AS date_text, NULL AS nothing;

• Numbers are written without quotes.
• Text and dates use single quotes. MySQL dates are written 'YYYY-MM-DD'.
• NULL means “no value” and has its own lesson: NULL Values.

Comments

Comments are ignored by the database. Use them to explain why a query does something.

-- single-line comment: everything after "-- " is ignoredSELECT first_name,      -- the employee's first name       salary           /* monthly salary in rupees */FROM employees/* a multi-line comment   can span several lines */WHERE emp_id IN (101, 102);

Naming conventions

• Use lower case with underscores: order_items, hire_date.
• Make names describe the data: salary, not s1.
• Pick singular or plural table names and stay consistent. This tutorial uses plural (employees).
• Avoid reserved words like order, group or select as names; you would have to quote them everywhere.

SQL syntax FAQ