Learn UNION and UNION ALL: THE VAULT

THE VAULT is chapter 14 and the set-operators chapter. DOMESTIC_OPS and FOREIGN_OPS share the same structure: OP_NAME, REGION, STATUS, BUDGET. UNION ALL stacks them into one result, duplicates included; plain UNION deduplicates the operations both agencies happen to run.

The missions walk through exactly that choice: combine everything, then dedupe, then unify only the active operations. Knowing when the duplicates matter is the whole lesson, and it is a distinction interviewers love to probe. You will also see why the column lists on both sides of a UNION have to line up.

One more door after this one, and it leads to the final mission.

This is the shape of query you practice here, not the answer to any mission. The real stages come with their own data, objectives, and hints.

SELECT OP_NAME, REGION FROM DOMESTIC_OPS
UNION
SELECT OP_NAME, REGION FROM FOREIGN_OPS;