Fix bogus logic for combining range-partitioned columns during pruning.

gen_prune_steps_from_opexps's notion of how to do this was overly
complicated and underly correct.

Per discussion of a report from Alan Jackson (though this fixes only one
aspect of that problem).  Back-patch to v11 where this code came in.

Amit Langote

Discussion: https://postgr.es/m/FAD28A83-AC73-489E-A058-2681FA31D648@tvsquared.com

src/test/regress/expected/partition_prune.out

@@ -3123,6 +3123,33 @@ select * from stable_qual_pruning
 (4 rows)
 
 drop table stable_qual_pruning;
+--
+-- Check that pruning with composite range partitioning works correctly when
+-- it must ignore clauses for trailing keys once it has seen a clause with
+-- non-inclusive operator for an earlier key
+--
+create table mc3p (a int, b int, c int) partition by range (a, abs(b), c);
+create table mc3p0 partition of mc3p
+  for values from (0, 0, 0) to (0, maxvalue, maxvalue);
+create table mc3p1 partition of mc3p
+  for values from (1, 1, 1) to (2, minvalue, minvalue);
+create table mc3p2 partition of mc3p
+  for values from (2, minvalue, minvalue) to (3, maxvalue, maxvalue);
+insert into mc3p values (0, 1, 1), (1, 1, 1), (2, 1, 1);
+explain (analyze, costs off, summary off, timing off)
+select * from mc3p where a < 3 and abs(b) = 1;
+                   QUERY PLAN                    
+-------------------------------------------------
+ Append (actual rows=3 loops=1)
+   ->  Seq Scan on mc3p0 (actual rows=1 loops=1)
+         Filter: ((a < 3) AND (abs(b) = 1))
+   ->  Seq Scan on mc3p1 (actual rows=1 loops=1)
+         Filter: ((a < 3) AND (abs(b) = 1))
+   ->  Seq Scan on mc3p2 (actual rows=1 loops=1)
+         Filter: ((a < 3) AND (abs(b) = 1))
+(7 rows)
+
+drop table mc3p;
 -- Ensure runtime pruning works with initplans params with boolean types
 create table boolvalues (value bool not null);
 insert into boolvalues values('t'),('f');

src/test/regress/sql/partition_prune.sql

@@ -792,6 +792,25 @@ select * from stable_qual_pruning
 
 drop table stable_qual_pruning;
 
+--
+-- Check that pruning with composite range partitioning works correctly when
+-- it must ignore clauses for trailing keys once it has seen a clause with
+-- non-inclusive operator for an earlier key
+--
+create table mc3p (a int, b int, c int) partition by range (a, abs(b), c);
+create table mc3p0 partition of mc3p
+  for values from (0, 0, 0) to (0, maxvalue, maxvalue);
+create table mc3p1 partition of mc3p
+  for values from (1, 1, 1) to (2, minvalue, minvalue);
+create table mc3p2 partition of mc3p
+  for values from (2, minvalue, minvalue) to (3, maxvalue, maxvalue);
+insert into mc3p values (0, 1, 1), (1, 1, 1), (2, 1, 1);
+
+explain (analyze, costs off, summary off, timing off)
+select * from mc3p where a < 3 and abs(b) = 1;
+
+drop table mc3p;
+
 -- Ensure runtime pruning works with initplans params with boolean types
 create table boolvalues (value bool not null);
 insert into boolvalues values('t'),('f');