Also how do LEFT JOIN
, RIGHT JOIN
and FULL JOIN
fit in?
Sql – the difference between “INNER JOIN” and “OUTER JOIN”
databaseinner-joinjoin;outer-joinsql
Related Topic
- Sql – the difference between Left, Right, Outer and Inner Joins?
- Sql – Difference between JOIN and INNER JOIN
- Mysql – INNER JOIN ON vs WHERE clause
- R – How to join (merge) data frames (inner, outer, left, right)
- C# – LEFT OUTER JOIN in LINQ
- Mysql – How to do a FULL OUTER JOIN in MySQL
- Sql – How to delete using INNER JOIN with SQL Server
Best Answer
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.
Examples
Suppose you have two tables, with a single column each, and data as follows:
Note that (1,2) are unique to A, (3,4) are common, and (5,6) are unique to B.
Inner join
An inner join using either of the equivalent queries gives the intersection of the two tables, i.e. the two rows they have in common.
Left outer join
A left outer join will give all rows in A, plus any common rows in B.
Right outer join
A right outer join will give all rows in B, plus any common rows in A.
Full outer join
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.