Assuming
you're joining on columns with no duplicates, this the most common
case:

- An inner join of table One and Two gives the result of One intersect Two, i.e. the inner part of a venn diagram intersection.
- An outer join of One and Two gives the results of One union Two, 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:

`One Two`

`- -`

`1`

` `

`3`

`2`

` `

`4`

`3`

` `

`5`

`4`

` `

`6`

Note
that (1,2) are unique to One, (3,4) are common, and (5,6) are unique
to Two.

**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.

`select`

` * `

`from`

` One `

`INNER`

` `

`JOIN`

` Two `

`on`

` One.One = Two.Two;`

`One | Two`

`3`

` | `

`3`

`4`

` | `

`4`

**Left outer join**
A
left outer join will give all rows in One, plus any common rows in
Two.

`select`

` * `

`from`

` One `

`LEFT`

` `

`OUTER`

` `

`JOIN`

` Two `

`on`

` One.One = Two.Two;`

`One | Two `

`--+-----`

`1`

` | `

`null`

`2`

` | `

`null`

`3`

` | `

`3`

`4`

` | `

`4`

**Right outer join**
A
right outer join will give all rows in Two, plus any common rows in
One.

`select`

`*`

`from`

`One`

`LEFT`

`OUTER`

`JOIN`

`Two`

`on`

`One.One = Two.Two;`

`One | Two`

`--+-----`

`3`

`|`

`3`

`4`

`|`

`4`

`null`

`|`

`5`

`null`

` | `

`6`

**Full outer join**
A
full outer join will give you the union of Two and One, i.e. All the
rows in One and all the rows in Two. If something in One doesn't have
a corresponding value in Two, then the Two portion is null, and vice
versa.

`select`

`*`

`from`

`One`

`FULL`

`OUTER`

`JOIN`

`Two on One.One = Two.Two;`

`One`

`| Two`

`-----+-----`

`1`

`|`

`null`

`2`

`|`

`null`

`3`

`|`

`3`

`4`

`|`

`4`

`null`

`|`

`5`

` null`

` | `

`6`