SQL · Lesson 3 of 8

WHERE, ORDER BY, LIMIT, narrowing the noise

10 min readUpdated 24 Jun 2026

A SELECT without WHERE is like walking into a library and asking for "all the books." Technically correct, practically useless. WHERE is how you filter. ORDER BY is how you sort. LIMIT is how you stop the database from drowning you in rows.

These three clauses show up in every real query you will ever write. Let us learn them properly.

WHERE: the filter

WHERE follows FROM. Read it as a sentence: "from this table, where this condition is true."

sql

SELECT name, city FROM customers
WHERE city = 'Mumbai';

The operators you actually use:

= equals. Strings need single quotes, numbers do not.
!= or <> not equals. Both work, pick one and stay consistent.
<, >, <=, >= the usual suspects, for numbers and dates.
BETWEEN a AND b inclusive range. BETWEEN 100 AND 500 includes both endpoints.
IN (...) one of these values. Cleaner than chaining ORs.
LIKE '%chai%' pattern match. % is "anything," _ is "exactly one character."
IS NULL / IS NOT NULL NULL is special. = NULL does not work, ever.

NULL is not a value. It is the absence of a value. WHERE column = NULL always returns nothing. Use IS NULL. I have debugged this exact bug for senior engineers more times than I care to admit.

Combining conditions

Chain with AND and OR. Wrap with parentheses when you mix them, because precedence will bite you.

sql

SELECT * FROM orders
WHERE city = 'Bengaluru'
  AND (status = 'delivered' OR status = 'out_for_delivery');

Without the parentheses, the OR would slip past the AND and you would get every "out_for_delivery" order in the country.

ORDER BY: sort it

By default, databases give you rows in whatever order they feel like. If you want a specific order, you have to ask.

sql

SELECT name, total FROM orders
ORDER BY total DESC;

ASC ascending (default, smallest first).
DESC descending, biggest first. The one you actually want most of the time.
Multi-column: ORDER BY city ASC, total DESC sorts by city, then within each city sorts by total descending.

LIMIT and OFFSET: pagination

You do not want all 4 million orders. You want the first 20.

sql

SELECT name, total FROM orders
ORDER BY created_at DESC
LIMIT 20 OFFSET 40;

LIMIT 20 give me 20 rows.
OFFSET 40 skip the first 40. So this is page 3 if your page size is 20.

Always pair LIMIT with ORDER BY. Without sorting, "the first 20" is meaningless. The database could return any 20.

Try it on the right

Three assignments waiting. They build on each other, do them in order. Next up: JOINs, where SQL gets actually interesting.

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Try this (0 of 3 done)

1
Show the 3 orders with the highest total, descending.
hint
ORDER BY total DESC, then LIMIT 3.
show answer
SELECT * FROM orders ORDER BY total DESC LIMIT 3;
2
Find all orders where the total is between 300 and 500 (inclusive).
hint
WHERE total BETWEEN 300 AND 500
show answer
SELECT * FROM orders WHERE total BETWEEN 300 AND 500;
3
Show all cancelled orders.
show answer
SELECT * FROM orders WHERE status = 'cancelled';