VietMX Staff asked 3 years ago
Problem
Also how do LEFT JOIN, RIGHT JOIN and FULL JOIN fit in?
Assuming you’re joining on columns with no duplicates, which is a very common case:
- An inner join of A and B gives the result of A intersect B, i.e. the inner part of a Venn diagram intersection.
- An outer join of A and B gives the results of A union B, i.e. the outer parts of a Venn diagram union.
- A left outer join will give all rows in A, plus any common rows in B.
- A right outer join will give all rows in B, plus any common rows in A.
- A full outer join will give you the union of A and B, i.e. all the rows in A and all the rows in B. If something in A doesn’t have a corresponding datum in B, then the B portion is null, and vice versa.
