ITPEC FE Morning April 2018 Question 28
ITPEC FE Morning April 2018 — Question 28 of 80
Sort-Merge Join — both tables are sorted by the join column, then merged sequentially.
How it works:
- Step 1: Sort both tables by the join column
- Step 2: Merge them in a single pass from top to bottom (like the merge phase in merge sort)
Why not others:
- (b) — describes index join (uses an index on one table to look up matching rows)
- (c) — describes nested loop join (iterate through one table, search the other for each row)
- (d) — describes hash join (build a hash table from one table, probe it with the other)
Key rule: The name says it all — sort first, then merge. Three main join methods in RDBMS: nested loop, sort-merge, and hash join.
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