SELECT and WHERE

~320 words · 2 min read

Asking questions of your data

Every SQL query is a question. SELECT chooses which columns to answer with; WHERE chooses which rows to include. Master these two clauses and you can answer most business questions.

Selecting columns

SELECT name, email, signup_date
FROM users;

Use * to select everything, but prefer naming columns explicitly — it makes the query faster and self-documenting, and it won't silently break if new columns are added later.

Filtering with WHERE

The WHERE clause keeps only the rows that match a condition:

SELECT name, email
FROM users
WHERE status = 'active'
  AND signup_date >= '2024-01-01';

Comparison and logical operators

= equal, <> not equal
<, >, <=, >= ordering
AND, OR, NOT combine conditions
IS NULL / IS NOT NULL — null checks (never use = NULL)
IN ('a', 'b', 'c') — membership in a list
BETWEEN x AND y — inclusive range
LIKE 'pre%' — pattern match (% = any chars)

NULL means "unknown", not "zero" or "empty". NULL = NULL is not true — always use IS NULL to test for it.

Sorting and limiting

SELECT name, score
FROM players
ORDER BY score DESC, name ASC
LIMIT 10;

ORDER BY sorts the final result; LIMIT caps how many rows come back. Together they answer "show me the top 10".

JOINs