Mixed set operators without parentheses

Question

Accepted Answer

INTERSECT has higher precedence than UNION, so the engine evaluates `b INTERSECT c` first, which yields just {2}. Then it computes `a UNION {2}`, giving {1, 2}. Most people assume left-to-right evaluation and expect {1, 2, 3, 4} INTERSECT c = {2, 4}, which is wrong. Use parentheses to make intent explicit: `(a UNION b) INTERSECT c` would give {2}.