intermediate

Query builder

Compose typed or fluent SQL while preserving control over joins, filters, ordering, pagination, and execution plans.

A query builder composes SQL through functions or a fluent API, often with parameter binding and optional type inference. It shines for dynamic filters, joins, and pagination without string concatenation.

					db.selectFrom('orders')
  .innerJoin('customers', 'customers.id', 'orders.customer_id')
  .where('orders.status', '=', status)
  .limit(pageSize)
  .offset(page * pageSize);

On interviews: explain optional filters, joins, pagination, SQL injection safety, and why builders still require index and plan knowledge.

Common pitfalls: fluent APIs that hide inefficient joins; unreadable dynamic queries; logging disabled in production so bad SQL stays invisible.

The trade-off is safer dynamic SQL and reuse versus readability and plan discipline.

Checklist:

Inspect generated SQL.
Parameterize dynamic values.
Tie query shape to indexes and pagination.
Log or trace important access paths.