Correlated subqueries (EXISTS)

Concepts: sqlExists

Watch how each order probes the subquery: the outer row expands, the payments table responds, and only rows with a qualifying payment move into the result. Each outer row probes the subquery independently. As soon as a qualifying payment is found, the subquery stops scanning and the order passes through. Orders with no matching payment are excluded entirely. EXISTS Efficiency Which subquery approach checks for related rows more efficiently?