Hi all,
I want to add a column, i.e. an additional TargetEntry, in an executor node named Foo that is placed on top of the
usuallycreated plan. This node Foo will calculate the column which is then used to sort the relation subsequently. If
desired,the column added by Foo is finally removed by a projection node, and might thus be a junk col.
(Projection
that removes bar,
if desired)||
Sort,
sorts by bar||
Foo,
adds column bar||
Usual
Plan||
...
How do I add an additional TargetEntry in my Foo node? Unfortunately, it does not suffice to simply append the
TargetEntryafter copying the child's targetlist in make_foo(Plan *). (I tested it and seems that some client side code
complainsabout 'advertised_#cols != actual_#cols')
How do I compute/evaluate the column? I just see ExecProject which evaluates the _whole_ targetlist with
ExecTargetList.But I would like to retrieve a tuple from the child node, evaluate my expression, wrap it into a
TargetEntryand append it to the tuple. Iterate.
Regards,
Peter