EXISTS vs IN
Both can test membership; EXISTS expresses a correlated relationship clearly.
EXISTS
Use it when
Use EXISTS when checking whether related rows exist.
IN
Use it when
Be careful with NOT IN when NULL values can appear.
Decision rule
Choose the option that matches the real requirement, data size, maintainability needs and compatibility constraints. Avoid selecting a technique only because it is familiar.
Need clarity?Prefer the simpler option that expresses the business rule directly.
Verify before scaling
Run both approaches on a small known dataset if the difference affects financial, inventory or operational decisions. Equivalent-looking techniques can behave differently with duplicates, blanks, NULL values or version constraints.