Re: How to look at the Expression Trees - Mailing list pgsql-hackers

Yes. There's actually two "trees" involved. The planner produces a tree of Expr nodes, and ExecInitExpr prepares a tree of ExprState nodes that mirrors the first tree. The ExprStates contain run-time state needed to execute the Expr tree.

5. The most common nodes in the expression trees are the ExecEvalVar,
ExecEvalConst and ExecEvalParam.

Well, that's obviously going to depend on the query.

I might be wrong somewhere (especially most people would be able to say
a lot about the 5th point). But if the above were to be correct then how
and why are the ExecMakeFunctionResultNoSets, ExecEvalRelabelType,
ExecEvalFuncArgs and the likes are used?

ExecMakeFunctionResultNoSets is used to evaluate function calls. The first function call invocation always uses ExecMakeFunctionResult, but if ExecMakeFunctionResult sees on that first invocation that it was not a set-returning-function, it changes the evaluator function for subsequent invocations to ExecMakeFunctionResultNoSets. ExecMakeFunctionResultNoSets does the same thing as ExecMakeFunctionResult, but skips the checks for set-returning functions, making the evaluation a bit faster.

ExecEvalFuncArgs is used by ExecMakeFunctionResult to evaluate the function arguments.

ExecEvalRelabelType is used to evaluate RelabelType nodes. RelabelType doesn't really do anything, it's just a placeholder when a type is cast to another, and the source and target types are binary compatible.

I wanted to see how the expression tree gets into form before it gets
into the ExecQual for parse by ExecEvalExpr function. Is there a way to
see the Expression Tree so that I get a better idea about what is
happening?

set debug_print_plan=on

--
 Heikki Linnakangas
 EnterpriseDB   http://www.enterprisedb.com