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 1.…