Fix plpgsql's handling of simple expressions in scrollable cursors.

exec_save_simple_expr did not account for the possibility that
standard_planner would stick a Materialize node atop the plan
of even a simple Result, if CURSOR_OPT_SCROLL is set.  This led
to an "unexpected plan node type" error.

This is a very old bug, but it'd only be reached by declaring a
cursor for a "SELECT simple-expression" query and explicitly
marking it scrollable, which is an odd thing to do.  So the lack
of prior reports isn't too surprising.

Bug: #18859
Reported-by: Olleg Samoylov <[email protected]>
Author: Andrei Lepikhov <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Discussion: https://postgr.es/m/18859-0d5f28ac99a37059@postgresql.org
Backpatch-through: 13

diff --git a/src/pl/plpgsql/src/expected/plpgsql_simple.out b/src/pl/plpgsql/src/expected/plpgsql_simple.out
index 7b22e60f1984ff07c526673212510c94cb58ee46..da351873e742e56dfc455d86541235f378d83588 100644 (file)
--- a/src/pl/plpgsql/src/expected/plpgsql_simple.out
+++ b/src/pl/plpgsql/src/expected/plpgsql_simple.out
@@ -118,3 +118,14 @@ select simplecaller();
            44
 (1 row)
 
+-- Check handling of simple expression in a scrollable cursor (bug #18859)
+do $$
+declare
+ p_CurData refcursor;
+ val int;
+begin
+ open p_CurData scroll for select 42;
+ fetch p_CurData into val;
+ raise notice 'val = %', val;
+end; $$;
+NOTICE:  val = 42

diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index ac87e6b83bb01231b5899eae91d21dfb9d0244e7..6469807a078c5bae959430dd346d6c9ba027dee8 100644 (file)
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -8136,10 +8136,12 @@ exec_save_simple_expr(PLpgSQL_expr *expr, CachedPlan *cplan)
    /*
     * Ordinarily, the plan node should be a simple Result.  However, if
     * force_parallel_mode is on, the planner might've stuck a Gather node
-    * atop that.  The simplest way to deal with this is to look through the
-    * Gather node.  The Gather node's tlist would normally contain a Var
-    * referencing the child node's output, but it could also be a Param, or
-    * it could be a Const that setrefs.c copied as-is.
+    * atop that; and/or if this plan is for a scrollable cursor, the planner
+    * might've stuck a Material node atop it.  The simplest way to deal with
+    * this is to look through the Gather and/or Material nodes.  The upper
+    * node's tlist would normally contain a Var referencing the child node's
+    * output, but it could also be a Param, or it could be a Const that
+    * setrefs.c copied as-is.
     */
    plan = stmt->planTree;
    for (;;)
@@ -8157,7 +8159,7 @@ exec_save_simple_expr(PLpgSQL_expr *expr, CachedPlan *cplan)
                   ((Result *) plan)->resconstantqual == NULL);
            break;
        }
-       else if (IsA(plan, Gather))
+       else if (IsA(plan, Gather) || IsA(plan, Material))
        {
            Assert(plan->lefttree != NULL &&
                   plan->righttree == NULL &&

diff --git a/src/pl/plpgsql/src/sql/plpgsql_simple.sql b/src/pl/plpgsql/src/sql/plpgsql_simple.sql
index 143bf09dce4694e2ce003f9b0aa9b89f6ca38db4..72d8afe4500d13ee13acac4f1b82601bb1032e55 100644 (file)
--- a/src/pl/plpgsql/src/sql/plpgsql_simple.sql
+++ b/src/pl/plpgsql/src/sql/plpgsql_simple.sql
@@ -102,3 +102,15 @@ as $$select 22 + 22$$;
 select simplecaller();
 
 select simplecaller();
+
+-- Check handling of simple expression in a scrollable cursor (bug #18859)
+
+do $$
+declare
+ p_CurData refcursor;
+ val int;
+begin
+ open p_CurData scroll for select 42;
+ fetch p_CurData into val;
+ raise notice 'val = %', val;
+end; $$;