AND & OR

Real questions usually have more than one rule. "Indian players and more than 400 runs." "MI players or anyone with 800+ runs." The logical operators AND and OR glue simple conditions together into one bigger condition.

Definition

A logical operator combines (or reverses) Boolean conditions and returns TRUE, FALSE or UNKNOWN.

• AND returns TRUE only when all the combined conditions are TRUE.
• OR returns TRUE when at least one of the combined conditions is TRUE.

In simple words: AND makes the filter stricter (fewer rows — every test must pass), OR makes it looser (more rows — any one test is enough).

Syntax

SELECT column_list
FROM table_name
WHERE condition1 AND condition2;   -- both must be TRUE

SELECT column_list
FROM table_name
WHERE condition1 OR condition2;    -- at least one must be TRUE

You can chain as many as you like: c1 AND c2 AND c3, c1 OR c2 OR c3.

Truth tables

(UNKNOWN comes from NULL. Since WHERE keeps only TRUE, UNKNOWN rows are dropped.)

Example — AND: India AND runs > 400

SELECT *
FROM players
WHERE country = 'India'
  AND runs > 400;

How it works: each row must pass both tests. MS Dhoni is Indian but has 350 runs → fails the runs test. Jos Buttler has 850 runs but is from England → fails the country test.

Example — OR: MI players OR 800+ runs

SELECT *
FROM players
WHERE team = 'MI'
   OR runs >= 800;

Rows pass if either condition is true: Rohit and Bumrah pass because of MI, Buttler passes because of 850 runs. OR returns more rows.

Example — the impossible AND

SELECT name, team
FROM players
WHERE team = 'MI'
  AND team = 'CSK';

Result: no rows. A single row's team can't be MI and CSK at the same time. When you mean "players from MI and CSK" in English, SQL needs OR (or IN): team = 'MI' OR team = 'CSK'.

Common mistakes

• ❌ Translating English "and" directly: "MI and CSK players" → team = 'MI' AND team = 'CSK' (0 rows). ✅ team = 'MI' OR team = 'CSK' or team IN ('MI', 'CSK').
• ❌ WHERE team = 'MI' OR 'CSK' → each side of OR must be a full condition. ✅ team = 'MI' OR team = 'CSK'.
• ❌ WHERE runs > 400 AND < 800 → the column must be repeated. ✅ runs > 400 AND runs < 800 (or BETWEEN).
• ❌ Mixing AND and OR without brackets — see the Precedence & Parentheses topic.

Interview tip

Q: A query with 2 conditions joined by AND returns 10 rows. If you change AND to OR, can it return fewer rows? A: No. Every row that passes A AND B also passes A OR B, so OR returns the same or more rows.