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Table A has the keys a, b, c and d with the values u = 1, 2, 3, 4.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Table A has the keys a, b, c and d with the values u = 1, 2, 3, 4. Table B has the keys b, c and e with the values v = 10, 20, 30. Find the number of rows after a merge on the key with how equal to "inner", "left", "right" and "outer". Say what each one keeps.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Build the two tables, and merge four times.
Check. The keys in both tables are b and c.
innerkeeps only the keys that are in both tables: 2 rows.leftkeeps all the keys of A, withNaNfor thevthat B does not have: 4 rows.rightkeeps all the keys of B: 3 rows.outerkeeps all the keys of both: a, b, c, d, e, which is 5 rows.
Answer: 2, 4, 3 and 5 rows.
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