SELECT, WHERE & ORDER BY

SQL (Structured Query Language) is how we talk to relational databases like MySQL. A database stores data in tables of rows and columns, and almost every question you will ever ask starts with SELECT.

The examples use an employees(id, name, city, department, salary, joined_on, manager_id) table.

The shape of a query

SELECT name, city, salary
FROM employees
WHERE city = 'Pune' AND salary > 50000
ORDER BY salary DESC
LIMIT 10;

Read it as: take the employees table, keep only rows that pass the WHERE test, show these three columns, sort them, and return the first ten. Every MySQL statement ends with a semicolon.

Choosing columns

SELECT * FROM employees;                      -- every column: fine while exploring
SELECT DISTINCT city FROM employees;          -- unique cities only
SELECT name AS employee, salary * 12 AS annual_ctc
FROM employees;                               -- expressions and aliases

Avoid SELECT * in application code: it moves columns you do not need and breaks the day the table changes.

Filtering with WHERE

Operator	Example
= , <>	department = 'Sales'
> < >= <=	salary >= 60000
BETWEEN	salary BETWEEN 30000 AND 60000 (inclusive)
IN	city IN ('Delhi', 'Pune', 'Kochi')
LIKE	name LIKE 'A%' (starts with A), '%kumar%'
IS NULL	manager_id IS NULL
NOT	city NOT IN ('Delhi')

Combine tests with AND and OR, and use brackets when you mix them, because AND binds more tightly than OR.

SELECT name, city, salary
FROM employees
WHERE department = 'Sales'
  AND (city = 'Mumbai' OR city = 'Surat')
  AND joined_on >= '2024-04-01';

Text comparisons are case-insensitive under MySQL 8's default utf8mb4_0900_ai_ci collation, so 'pune' matches 'Pune'.

NULL is not a value

NULL means "unknown", and any comparison with it is unknown too, so salary = NULL never matches. Use IS NULL and IS NOT NULL, and COALESCE(bonus, 0) to substitute a default.

Sorting and paging

SELECT name, department, salary
FROM employees
ORDER BY department ASC, salary DESC
LIMIT 20 OFFSET 40;       -- rows 41-60, i.e. page 3

ORDER BY accepts several columns, an alias, or an expression. Without it, row order is not guaranteed.

The order MySQL really works in

Step	Clause
1	FROM
2	WHERE
3	GROUP BY
4	HAVING
5	SELECT (aliases are created here)
6	ORDER BY
7	LIMIT

That is exactly why an alias defined in SELECT may be used in ORDER BY but not in WHERE.

Common mistakes

• Quoting text with double quotes; MySQL convention is single quotes, 'Pune'.
• Writing = NULL instead of IS NULL.
• Expecting BETWEEN '2026-01-01' AND '2026-01-31' to include a DATETIME at 10:30 on the 31st — it does not.
• Leading wildcards such as LIKE '%sharma', which cannot use an index.
• Forgetting LIMIT while exploring a million-row table.