joins

SQL joins combine data from multiple tables. INNER JOIN returns matching rows only. LEFT/RIGHT JOIN includes all rows from one table, nulls for non-matches. FULL OUTER JOIN combines both. I use CROSS JOIN for Cartesian products sparingly—performance k

LATERAL joins enable correlated subqueries in FROM clause. Each row can reference previous table columns. I use LATERAL for top-N-per-group queries. CROSS JOIN LATERAL iterates for each row. LEFT JOIN LATERAL includes rows without matches. Understandi

Merges are where silent data corruption often begins. I prefer explicit key audits, join cardinality validation, and indicator columns when investigating row loss or duplication. In production analytics, proving that a join is one_to_one or many_to_on