1 · Read the data · 12 MIN

Combine conditions without guessing precedence

AND requires both conditions; OR accepts either.

Complex filters are easier to understand when grouped with parentheses. The sample requires both a chosen city and enough points. AND binds more tightly than OR in SQL, but relying on remembered precedence can hide mistakes. Use parentheses to state the intended grouping and evaluate each row explicitly. A row with an unknown city does not satisfy city = Delhi. The next lesson explains why unknown values need a different comparison.

Keep the source rows visible. Predict which rows and columns will remain after each operation.

Before you start

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New words, explained

AND: Both conditions must be true.
OR: At least one condition must be true.
precedence: The order in which operators are grouped.

Follow the example step by step

Evaluate city and points as two separate questions for each row.
Combine with AND and retain only Grace.
Use parentheses around the city alternatives for the change task.
For the build task, either one of its two conditions is enough.

Practice table: learners
id	name	city	points
1	Ada	Delhi	20
2	Lin	NULL (unknown)	0
3	Grace	Delhi	35
4	Sam	Pune	20

Practice table: enrollments
learner_id	course
1	React
1	SQL
3	SQL

You are ready to move on when: Return names where city is Delhi OR points is zero, ordered by id. The zero-point learner must be included even with an unknown city.

Read the example

SELECT name FROM learners
WHERE city = 'Delhi' AND points >= 30
ORDER BY id;

Check the expected output

[["Grace"]]

Your challenge

Return names where city is Delhi OR points is zero, ordered by id. The zero-point learner must be included even with an unknown city.

Common trap

A missing pair of parentheses can allow rows that should fail another condition.

Open interactive exercise →See the syllabus

Further reading: SQLite SELECT reference

Next lesson: Understand unknown values and NULL →