Re: SQL Exists for Flag

[Vern Hamberg <vhamberg@xxxxxxxxxxxxxxx>]

Nice chart. It doesn't quite fit the kinds of JOIN we have, or we use a different name. We have an EXCEPTION JOIN, which is like that LEFT OUTER JOIN that excludes the records that don't have a NULL from the 2nd table, right?

----- Original Message -----
Nice Charles!


On Thu, Jun 20, 2013 at 2:05 PM, Charles Wilt <charles.wilt@xxxxxxxxx>wrote:

> http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html
>
> Charles
>
>
> On Thu, Jun 20, 2013 at 1:52 PM, Michael Ryan <michaelrtr@xxxxxxxxx>
> wrote:
>
> > I certainly was! I don't know why I can't get my head around this stuff
> > sometimes. Maybe it's a vitamin deficiency.
> >
> >
> > On Thu, Jun 20, 2013 at 1:42 PM, Vern Hamberg <vhamberg@xxxxxxxxxxxxxxx
> > > wrote:
> >
> > > Woohoo! You made me almost do a happy dance!
> > >
> > > ----- Original Message -----
> > > Wonderful...it works! Thanks Vern (and Charles). Seeing the straight
> > select
> > > with the left outer join helped me see it Vern. Yay!
> > >
> > >
> > > On Thu, Jun 20, 2013 at 1:33 PM, Vern Hamberg <
> vhamberg@xxxxxxxxxxxxxxx
> > > > wrote:
> > >
> > > > Hi Michael
> > > >
> > > > Let's see if I can make sense of this - a LEFT OUTER JOIN gives you
> all
> > > > records from the first table, plus any matching records from the
> second
> > > > table.
> > > >
> > > > So the JOIN accomplishes the EXISTS condition. If FLD1 exists in
> > TableB,
> > > > there will be values there.
> > > >
> > > > When there is not a matching record - FLD1 is not in TableB, then the
> > > > column TAbleB/Fld1 will be NULL. So the CASE tests for that and sets
> > > either
> > > > 'X' or a blank.
> > > >
> > > > You can get a better feel for it, perhaps, if you run this -
> > > >
> > > > select tablea.fld1, tablea.fld2, tableb.fld1 from tablea left outer
> > join
> > > > tableb on tablea.fld1 = tableb.fld1
> > > >
> > > > If I'm guessing right, you should see some hyphens in the 3rd column
> -
> > > > these are the NULLs for unmatched records.
> > > >
> > > > Vern
> > > >
> > > > ----- Original Message -----
> > > > Hey Vern -
> > > >
> > > > But the condition isn't that TableB.Fld1 is null, it's that the key
> > value
> > > > TableA.Fld1 is found in TableB.
> > > >
> > > >
> > > > On Thu, Jun 20, 2013 at 1:01 PM, Vern Hamberg <
> > vhamberg@xxxxxxxxxxxxxxx
> > > > > wrote:
> > > >
> > > > > Hi Michael
> > > > >
> > > > > That's what this should do - a LEFT OUTER JOIN will give you all
> > > records
> > > > > from TableA and TableB, if there is a match - NULLs, otherwise.
> > > > >
> > > > > Give it a try. You might like it almost as much as 7Up!
> > > > >
> > > > > Vern
> > > > >
> > > > > ----- Original Message -----
> > > > > Thanks guys...I didn't explain myself well. I want to display the
> > > values
> > > > > from TableA, and an 'X' if the key in TableA is found in TableB.
> > > > >
> > > > >
> > > > > On Thu, Jun 20, 2013 at 12:27 PM, Vern Hamberg <
> > > vhamberg@xxxxxxxxxxxxxxx
> > > > > > wrote:
> > > > >
> > > > > > Left outer JOIN, I think.
> > > > > >
> > > > > > select tablea.fld1, tablea.fld2, case when TableB.fld1 is null
> then
> > > ' '
> > > > > > else 'X' end from tablea join tableb on tablea.fld1 = tableb.fld1
> > > > > >
> > > > > > Check the syntax of the CASE - I'm doing this from memory.
> > > > > >
> > > > > > HTHAW (hope this helps and works)
> > > > > > Vern
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > Here's what I want to do...TableA has 4 columns. TableB shares a
> > key
> > > > > value
> > > > > > with TableA. I want to produce this output in a select statement
> > (to
> > > be
> > > > > > used from PHP fwiw):
> > > > > >
> > > > > > TableA.Fld1 TableA.Fld2 'X' (if TableA.Fld1 is in TableB).
> > > > > >
> > > > > > I've been trying combinations of a CTE, CASE, and exists, but I
> > can't
> > > > get
> > > > > > this to work. I'd like:
> > > > > >
> > > > > > A1 A2
> > > > > > A3 A4 X
> > > > > > A5 A6 X
> > > > > > A7 A8
> > > > > >
> > > > > > IOW, I want the values for TableA to show up, and an X if the
> > > > > corresponding
> > > > > > key value is in TableB. This has to be easier than I'm making it
> > out
> > > to
> > > > > be.
> > > > > > Thanks!
> > > > > > --
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