Thread: why there are two TargetEntrys in Query when i use "select count(catcode) from pois group by catcode"?

I've the table
CREATE TABLE pois
(
   uid integer not null,
   name VARCHAR(128),
   catcode VARCHAR(32)  not null,
   catname VARCHAR(32),
   others VARCHAR(32)
);
after i execute "select count(*) from pois group by catcode";
the log of query.targetList is :
:targetList (
          {TARGETENTRY
          :expr
             {AGGREF
             :aggfnoid 2803
             :aggtype 20
             :args <>
             :agglevelsup 0
             :aggstar true
             :aggdistinct false
             :location 7
             }
          :resno 1
          :resname count
          :ressortgroupref 0
          :resorigtbl 0
          :resorigcol 0
          :resjunk false
          }
          {TARGETENTRY
          :expr
             {VAR
             :varno 1
             :varattno 3
             :vartype 1043
             :vartypmod 36
             :varlevelsup 0
             :varnoold 1
             :varoattno 3
             :location 35
             }
          :resno 2
          :resname <>
          :ressortgroupref 1
          :resorigtbl 0
          :resorigcol 0
          :resjunk true
          }
       )
why there is the second TARGETENTRY? what's the purpose of the second TARGETENTRY?

sunpeng <bluevaley@gmail.com> writes:
> after i execute "select count(*) from pois group by catcode";
> the log of query.targetList is :
> why there is the second TARGETENTRY? what's the purpose of the second
> TARGETENTRY?

It's the GROUP BY expression.  Note the ressortgroupref and resjunk
settings.

            regards, tom lane