asked on

LEFT JOIN vs RIGHT JOIN ???

Someone please explain

LEFT JOIN

vs

RIGHT JOIN

Why do I care if something is LEFT JOINED vs RIGHT JOINED?

I need someone to put this in layman's terms, really dummy it up.

I am trying to progress beyond SELECT FROM WHERE which is about as advanced as I get in SQL knowledge right now.

Thanks,

Tom

ASKER CERTIFIED SOLUTION

TheNextStep

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nico5038

The LEFT/RIGHT join is used to show all table-entries from one table and only the matching of the other.
The direction you draw the line will influence the sequence of the "mandatory" tables mentioned in the pop-up and lead to a LEFT or RIGHT.
Effectively the "non-match" wizard delivers only half of the non-match, as having a right-join, the left-join gives also a "non-match" but then seen from the other table.
To get all non-matching records you need to have a right-join AND a left-join with in both the criteria that the non-mandatory table has nulls in it's unique key.
With a union of those two queries you get effectively what another SQL implementation would call a FULL OUTERJOIN.

Normally a JOIN gives automatically all matched, the LEFT "union" RIGHT gives the remaining set of rows.

Clear ?
No, read again and again and ....

Nic;o)

Paurths

i've been reading it 3.526 times now Nico,

i must admit, i s@ck at SQL...

;-) ;-) ;-) ;-) ;-) ;-) ;-) ;-) ;-) ;-)

nico5038

Ricky, too much Hoegaarden causes reading loops.... ;-)

Nic;o)

Paurths

Public Sub Freetime()

Dim strSQL as String
Dim strBrand as String
Dim rst as DAO.Recordset
Dim dbs as DAO.Database

Select Case Today
Case Friday
strBrand = "Hoegaarden"
Case Saturday
strBrand = "KasteelBier"
Case Sunday
strBrand = "Jupiler"
End Select

strSQL = "Select Glas, Bottle From Bar where Brand = " & chr(34) & strBrand & chr(34) & ";"

set dbs = CurrentCafe
set rst = dbs.Openrecordset(strSQL)

rst.moveFirst

While dbs = open

rst.Edit
rst.Drink
rst.update

rst.Movenext
Wend

set rst = empty
dbs.close
set dbs = empty

msgbox "Time to go home", vbOkonly + vbInformation, "C ya tomorrow"

End Sub

nico5038

SYNTAX-ERROR rst.Drink UNKNOWN PROPERTY ;-)

(Sorry for the interrupt knowlton)

Nic;o)

Tom Knowlton

ASKER

Thanks everyone.

btw - while I was waiting for a reply I found a cool tutorial at:

http://www.w3schools.com/sql/sql_join.asp