Subject Re: [firebird-support] Strange plan? Bug?
Author Kjell Rilbe
Den 2013-09-19 19:07 skrev Leyne, Sean såhär:
> > >I do expect more than on PLAN dues to the derived table and the union,
> > >but there seems to be a comma missing before the PLAN on line 05 at
> least.
> > >
> > >I don't really need to understand the plan, but I wanted to bring it up
> > >in case there's a bug that needs to be fixed...
> >
> > Hi Kjell, I doubt this is an error. The place you think a comma is
> missing, is
> > where your UNION is. I must admit that I've never before really noticed
> > whether or not there is a comma in the plan with union, but when I try
> Adding to Set's typically excellent comments, I would suggest that you
> look at using Common Table Expression (CTE) for your FE Företag inner
> join.
> The reason that the PLAN is showing a NATURAL access for FE Företag is
> because the SELECT from Företag is not getting the JOIN criteria,
> using a CTE would change that.

Strangely enough I SET's reply hasen't shown up in my inbox, and yes I
did check the spam/garbage folder. Anyway, I know separate subplans are
enumerated without comma, but it seems odd, then, that it doesn't prefix
*all* subplans with "PLAN". Shouldn't it appear like this?

02___JOIN (
03_____JOIN (
05_________PLAN FE Företag NATURAL
06_________PLAN JOIN (
07___________FE BIADR NATURAL,
08___________FE BI INDEX (IX_PK_Befattningsinnehav),
09___________FE BEF INDEX (IX_PK_Befattning)
12_______F INDEX (IX_PK_Företag),
13_______E INDEX (IX_PK_Epostadress),
14_______STATUS INDEX (IX_PK_Företagsstatus)
16_____JURFORM INDEX (IX_PK_JuridiskForm),
17_____BVSTATUS INDEX (IX_PK_BVstatus)

The lines 05-10 is the plan returned if only the derived table part is
executed alone (minus the FE prefixes for the table aliases of course).
Putting a paranthesis around that subplan makes sense, and makes the
wrapping join contain a correctly comma separated list of "items".
Without the paranthesis it's not clear that line 05 and lines 06-10 are
subplans that are unioned, and then joined.

At the least, it seems incorrect that line 05 is missing the "PLAN" prefix.


Kjell Rilbe
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