Re: How does postgres store the join predicate for a relation in a given query

On Tue, Oct 10, 2017 at 07:29:24PM +0530, Gourav Kumar wrote:
> When you fire a query in postgresql, it will first parse the query and
> create the data structures for storing various aspects of the query and
> executing the query. (Like RangeTblEntry, PlannerInfo, RangeOptInfo etc.).
>
> I want to know how does postgresql stores the join predicates of a query.
> Like which data structure is used to store the join predicates.
>
> How can we find the join predicates applied on a relation from relid, Oid
> or RangeTblEntry ?
>
> I want to construct a join graph for a given query, for which I need the
> join predicates between two relations.

In the usingClause or quals fields of a JoinExpr. See
src/backend/parser/gram.y, search for join_qual.

Of course, WHERE clauses have to be inspected as well, which go into the
whereClause of of a SelectStmt; search for where_clause in
src/backend/parser/gram.y.

Nico
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