diff options
Diffstat (limited to 'src/backend/optimizer/util/relnode.c')
| -rw-r--r-- | src/backend/optimizer/util/relnode.c | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c index 8ee5671a551..1f198201c32 100644 --- a/src/backend/optimizer/util/relnode.c +++ b/src/backend/optimizer/util/relnode.c @@ -677,6 +677,36 @@ subbuild_joinrel_joinlist(RelOptInfo *joinrel, /* + * build_empty_join_rel + * Build a dummy join relation describing an empty set of base rels. + * + * This is used for queries with empty FROM clauses, such as "SELECT 2+2" or + * "INSERT INTO foo VALUES(...)". We don't try very hard to make the empty + * joinrel completely valid, since no real planning will be done with it --- + * we just need it to carry a simple Result path out of query_planner(). + */ +RelOptInfo * +build_empty_join_rel(PlannerInfo *root) +{ + RelOptInfo *joinrel; + + /* The dummy join relation should be the only one ... */ + Assert(root->join_rel_list == NIL); + + joinrel = makeNode(RelOptInfo); + joinrel->reloptkind = RELOPT_JOINREL; + joinrel->relids = NULL; /* empty set */ + joinrel->rows = 1; /* we produce one row for such cases */ + joinrel->width = 0; /* it contains no Vars */ + joinrel->rtekind = RTE_JOIN; + + root->join_rel_list = lappend(root->join_rel_list, joinrel); + + return joinrel; +} + + +/* * find_childrel_appendrelinfo * Get the AppendRelInfo associated with an appendrel child rel. * |