عملگر EXISTS

EXISTS چیست؟

EXISTS بررسی می‌کند که آیا یک Subquery هیچ رکوردی برمی‌گرداند یا نه.

مثال: دانش‌آموزانی که نمره دارند

SELECT name FROM students AS s
WHERE EXISTS (
    SELECT 1 FROM scores AS sc
    WHERE sc.student_id = s.id
);

NOT EXISTS

SELECT name FROM students AS s
WHERE NOT EXISTS (
    SELECT 1 FROM scores AS sc
    WHERE sc.student_id = s.id
);