Interview Questions

An index is a data structure (often a B-tree) that speeds up reads by avoiding full table scans. Trade-off: it consumes storage and slows writes (inserts/updates must maintain the index), so index columns you frequently filter or join on.

`==` compares values after type coercion, so `0 == "0"` is true. `===` (strict equality) compares both value and type without coercion, so `0 === "0"` is false. Prefer `===` to avoid surprising coercion bugs.

`undefined` means a variable was declared but not assigned; `null` is an explicit 'no value' you assign intentionally. `typeof undefined` is 'undefined', `typeof null` is 'object' (a historical quirk).

Lists are mutable (you can change, add, remove items) and use more memory; tuples are immutable and slightly faster, usable as dict keys. Use tuples for fixed collections and lists for changing sequences.