If I create a class A and make subclasses A1 and A2, then
I get useful explanations when I say "EXPLAIN SELECT * FROM A1 ..."
but not if I ask about a query on the inheritance tree A*.

tgl=> EXPLAIN SELECT * FROM A* WHERE accountid = 3;
NOTICE:  QUERY PLAN:

Append  (cost=0.00 size=0 width=0)

EXPLAIN

With "explain verbose" it is possible to see that the APPEND plan
has substructure, but it's hard to see what's going on in that format.
How come plain "explain" doesn't show the subnodes of an APPEND plan?

			regards, tom lane

Tue, 14 Jul 1998 13:48:41 -0400
Tom Lane <tgl@sss.pgh.pa.us>
EXPLAIN doesn't explain operations on inheritance trees
> If I create a class A and make subclasses A1 and A2, then
> I get useful explanations when I say "EXPLAIN SELECT * FROM A1 ..."
> but not if I ask about a query on the inheritance tree A*.
> 
> tgl=> EXPLAIN SELECT * FROM A* WHERE accountid = 3;
> NOTICE:  QUERY PLAN:
> 
> Append  (cost=0.00 size=0 width=0)
> 
> EXPLAIN
> 
> With "explain verbose" it is possible to see that the APPEND plan
> has substructure, but it's hard to see what's going on in that format.
> How come plain "explain" doesn't show the subnodes of an APPEND plan?

I have just applied a patch to fix this.  Append is an unusual node,
because instead of checking left/right plans, you have to loop through a
list of plans.  EXPLAIN did not do this, nor did cost computations and
pprint().

Should be better now.  

I renamed all the Append structure names because they were very
confusing to me.  I had created some of them for UNION, but named the
badly.

-- 
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Wed, 15 Jul 1998 11:10:29 -0400 (EDT)
Bruce Momjian <maillist@candle.pha.pa.us>
Re: [HACKERS] EXPLAIN doesn't explain operations on inheritance trees