Choosing a JOIN type

Pick the right JOIN for each scenario.

Choosing join types

The right JOIN type depends on the question. Pick INNER for matches, LEFT for missing records.

SELECT * FROM a
LEFT JOIN b ON a.id = b.id;

All a rows appear.

All columns are selected from a. b ON is joined, keeping every row of the left table.

None is bad; each has its purpose. Row coverage and NULL requirements decide.

Choose INNER for matches only, LEFT to keep one side complete, FULL to keep both sides complete, and CROSS for every combination.

Use LEFT JOIN to keep all rows of a joined with b.

Show example solution

SELECT * FROM a
LEFT JOIN b ON a.id = b.id;

Pick join type

SELECT * FROM a
____ b ON a.id = b.id;

Show answer

SELECT * FROM a
LEFT JOIN b ON a.id = b.id;