LEFT JOIN vs. LEFT OUTER JOIN in SQL Server
LEFT JOIN vs. LEFT OUTER JOIN in SQL Server
LEFT JOIN vs. LEFT OUTER JOIN in SQL Server
Re: LEFT JOIN vs. LEFT OUTER JOIN in SQL Server
As per the documentation: [FROM (Transact-SQL)](http://msdn.microsoft.com/en-us/library/ms177634%28SQL.90%29.aspx):
```
::=
[ { INNER | { { LEFT | RIGHT | FULL } [ OUTER ] } } [ ] ]
JOIN
```
The keyword `OUTER` is marked as optional (enclosed in square brackets). In this specific case, whether you specify `OUTER` or not makes no difference. Note that while the other elements of the join clause is also marked as optional, leaving *them* out *will* make a difference.
For instance, the entire type-part of the `JOIN` clause is optional, in which case the default is `INNER` if you just specify `JOIN`. In other words, this is legal:
```
SELECT *
FROM A JOIN B ON A.X = B.Y
```
Here's a list of equivalent syntaxes:
```
A LEFT JOIN B A LEFT OUTER JOIN B
A RIGHT JOIN B A RIGHT OUTER JOIN B
A FULL JOIN B A FULL OUTER JOIN B
A INNER JOIN B A JOIN B
```
Also take a look at the answer I left on this other SO question: [SQL left join vs multiple tables on FROM line?](https://stackoverflow.com/a/894659/267).
```
::=
[ { INNER | { { LEFT | RIGHT | FULL } [ OUTER ] } } [ ] ]
JOIN
```
The keyword `OUTER` is marked as optional (enclosed in square brackets). In this specific case, whether you specify `OUTER` or not makes no difference. Note that while the other elements of the join clause is also marked as optional, leaving *them* out *will* make a difference.
For instance, the entire type-part of the `JOIN` clause is optional, in which case the default is `INNER` if you just specify `JOIN`. In other words, this is legal:
```
SELECT *
FROM A JOIN B ON A.X = B.Y
```
Here's a list of equivalent syntaxes:
```
A LEFT JOIN B A LEFT OUTER JOIN B
A RIGHT JOIN B A RIGHT OUTER JOIN B
A FULL JOIN B A FULL OUTER JOIN B
A INNER JOIN B A JOIN B
```
Also take a look at the answer I left on this other SO question: [SQL left join vs multiple tables on FROM line?](https://stackoverflow.com/a/894659/267).