Where

In the last lesson you chose which columns to return. Now you'll choose which rows . By the end of this lesson you'll filter any table with WHERE — comparing values, combining conditions with AND / OR / NOT , matching ranges and lists, finding text patterns, and handling missing data correctly.

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Part of the free SQL course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

This is the same products table from the SELECT lesson, so the results stay consistent. Every query below filters these six rows — keep them in front of you as you read.

A WHERE clause adds a condition to a query. The database checks that condition once for each row and keeps only the rows where it is true. Everything else is filtered out.

WHERE is the bouncer at a club. Each row walks up; if it meets the rule ( price 30 ), it gets in; if not, it's turned away. The table itself is never changed — you're just choosing who gets through for this one query.

There are six comparison operators. Note that "not equal to" is written in standard SQL (most databases also accept != ):

When you compare against text , wrap the value in single quotes ( 'Electronics' ). Numbers like 30 are written bare, with no quotes.

Fill in the blanks to list the name and price of every Electronics product. Remember: column name on the left, the text value in single quotes on the right. The expected result is in the comments so you can check yourself.

One condition is rarely enough. Logical operators let you chain several together:

AND — both must be true

"Electronics and under $20" → narrows the result down.

OR — either can be true

NOT — flips a condition

BETWEEN x AND y is shorthand for column x AND column y . It is inclusive : both end values count as matches. It reads cleanly and is perfect for prices, dates, and ages.

Fill in the two range values so the query returns products priced from $5 up to $20 (inclusive). Low value first, then the high value.

IN (a, b, c) is true when the column equals any value in the list. It replaces a long chain of OR s and is much easier to read.

LIKE searches text with two wildcards: % stands for any number of characters (including none), and _ stands for exactly one character. Use it for "starts with", "ends with", and "contains" searches.

NULL is SQL's way of saying "there is no value here" — unknown or missing. Because NULL is not really a value, you cannot test it with = or ; those always come back "unknown" and match nothing. Use IS NULL and IS NOT NULL instead.

Never write WHERE category = NULL — it silently returns zero rows. It's always WHERE category IS NULL .

They do the same thing — "not equal to". is the official SQL standard; != works in most databases too. Pick one and stay consistent.

Inclusive. price BETWEEN 10 AND 35 includes both 10 and 35. If you want to exclude an end, use plain comparisons like price 10 AND price 35 .

It depends on the database. SQLite and MySQL are usually case-insensitive for ASCII letters; PostgreSQL's LIKE is case-sensitive (use ILIKE there). To be safe, match the case of your data.

Q: Why does WHERE category = NULL return nothing?

NULL means "unknown", and comparing anything to "unknown" gives "unknown" — never true. That's why you need IS NULL instead of = .

Put it all together — a brief, a blank canvas, and the expected result in the comments. Write it, then copy it into a playground to confirm.

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