Choosing the right SQL data types is one of the quiet decisions that shapes storage , correctness , and query behavior in PostgreSQL. In a tight SQL screen, interviewers often follow up on why you picked a type—not only whether the query returns rows. This guide walks through the main families, common pitfalls (rounding, time zones, type mismatches), and how to reason about casts—using PostgreSQL syntax, the same dialect PipeCode uses for practice.

If you want hands-on reps after you read, explore practice → , drill SQL problems → , browse SQL by topic → , or open Zero to FAANG SQL (full fundamentals) → for a structured path.

On this page

Why column types matter

Numeric types

Text and binary

Boolean and NULL

Date and time

Semi-structured and other types

Casting and comparison rules

Choosing types (checklist)

Frequently asked questions

Practice on PipeCode

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