Logical operators
SQL Logical Operator Interview Questions
Logical operators are AND, OR and NOT, plus the rules about which of them applies first. They are how a sentence like "paid customers in the US, or anyone on a trial" becomes something a database can run.
What logical operator questions ask you to do
Across the questions here, these are the shapes that come up:
- Combine two groups of conditions with OR
- Apply one condition only when another one holds
- Exclude a combination rather than a single value
- Turn a requirement written in plain English into conditions
Common mistakes with logical operators
AND is applied before OR, which is rarely what people mean. Written without brackets, "country is US and tier is paid or tier is trial" returns every trial customer in the world, because the database reads it as "(US and paid) or trial". Brackets cost nothing and remove the ambiguity entirely.
Questions to practice
Questions last reviewed 19 October 2026.