As per the documentation: FROM (Transact-SQL):
<join_type> ::=
[ { INNER | { { LEFT | RIGHT | FULL } [ OUTER ] } } [ <join_hint> ] ]
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?.
Simple Example: Let's say you have a Students
table, and a Lockers
table. In SQL, the first table you specify in a join, Students
, is the LEFT table, and the second one, Lockers
, is the RIGHT table.
Each student can be assigned to a locker, so there is a LockerNumber
column in the Student
table. More than one student could potentially be in a single locker, but especially at the beginning of the school year, you may have some incoming students without lockers and some lockers that have no students assigned.
For the sake of this example, let's say you have 100 students, 70 of which have lockers. You have a total of 50 lockers, 40 of which have at least 1 student and 10 lockers have no student.
INNER JOIN
is equivalent to "show me all students with lockers".
Any students without lockers, or any lockers without students are missing.
Returns 70 rows
LEFT OUTER JOIN
would be "show me all students, with their corresponding locker if they have one".
This might be a general student list, or could be used to identify students with no locker.
Returns 100 rows
RIGHT OUTER JOIN
would be "show me all lockers, and the students assigned to them if there are any".
This could be used to identify lockers that have no students assigned, or lockers that have too many students.
Returns 80 rows (list of 70 students in the 40 lockers, plus the 10 lockers with no student)
FULL OUTER JOIN
would be silly and probably not much use.
Something like "show me all students and all lockers, and match them up where you can"
Returns 110 rows (all 100 students, including those without lockers. Plus the 10 lockers with no student)
CROSS JOIN
is also fairly silly in this scenario.
It doesn't use the linked lockernumber
field in the students table, so you basically end up with a big giant list of every possible student-to-locker pairing, whether or not it actually exists.
Returns 5000 rows (100 students x 50 lockers). Could be useful (with filtering) as a starting point to match up the new students with the empty lockers.
Best Answer
Solved it!
Final Output:
Here is the Scenario
1 - The Database
2 - The Data
3 - The Entity in VS.NET 2008
alt text http://i478.photobucket.com/albums/rr148/KyleLanser/companyproduct.png
The Entity Container Name is 'testEntities' (as seen in model Properties window)
4 - The Code (FINALLY!)
5 - The Final Output