Support FETCH FIRST WITH TIES

WITH TIES is an option to the FETCH FIRST N ROWS clause (the SQL
standard's spelling of LIMIT), where you additionally get rows that
compare equal to the last of those N rows by the columns in the
mandatory ORDER BY clause.

There was a proposal by Andrew Gierth to implement this functionality in
a more powerful way that would yield more features, but the other patch
had not been finished at this time, so we decided to use this one for
now in the spirit of incremental development.

Author: Surafel Temesgen <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Reviewed-by: Tomas Vondra <[email protected]>
Discussion: https://postgr.es/m/CALAY4q9ky7rD_A4vf=FVQvCGngm3LOes-ky0J6euMrg=_Se+ag@mail.gmail.com
Discussion: https://postgr.es/m/[email protected]

2 files changed, 215 insertions, 0 deletions

diff --git a/src/test/regress/expected/limit.out b/src/test/regress/expected/limit.out
index c18f547cbd3..a4e175855c3 100644
--- a/src/test/regress/expected/limit.out
+++ b/src/test/regress/expected/limit.out
@@ -286,6 +286,58 @@ fetch all in c4;
 ----+----
 (0 rows)
 
+declare c5 cursor for select * from int8_tbl order by q1 fetch first 2 rows with ties;
+fetch all in c5;
+ q1  |        q2        
+-----+------------------
+ 123 |              456
+ 123 | 4567890123456789
+(2 rows)
+
+fetch 1 in c5;
+ q1 | q2 
+----+----
+(0 rows)
+
+fetch backward 1 in c5;
+ q1  |        q2        
+-----+------------------
+ 123 | 4567890123456789
+(1 row)
+
+fetch backward 1 in c5;
+ q1  | q2  
+-----+-----
+ 123 | 456
+(1 row)
+
+fetch all in c5;
+ q1  |        q2        
+-----+------------------
+ 123 | 4567890123456789
+(1 row)
+
+fetch backward all in c5;
+ q1  |        q2        
+-----+------------------
+ 123 | 4567890123456789
+ 123 |              456
+(2 rows)
+
+fetch all in c5;
+ q1  |        q2        
+-----+------------------
+ 123 |              456
+ 123 | 4567890123456789
+(2 rows)
+
+fetch backward all in c5;
+ q1  |        q2        
+-----+------------------
+ 123 | 4567890123456789
+ 123 |              456
+(2 rows)
+
 rollback;
 -- Stress test for variable LIMIT in conjunction with bounded-heap sorting
 SELECT
@@ -503,3 +555,118 @@ select sum(tenthous) as s1, sum(tenthous) + random()*0 as s2
  45020 | 45020
 (3 rows)
 
+--
+-- FETCH FIRST
+-- Check the WITH TIES clause
+--
+SELECT  thousand
+		FROM onek WHERE thousand < 5
+		ORDER BY thousand FETCH FIRST 2 ROW WITH TIES;
+ thousand 
+----------
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+(10 rows)
+
+SELECT  thousand
+		FROM onek WHERE thousand < 5
+		ORDER BY thousand FETCH FIRST 1 ROW WITH TIES;
+ thousand 
+----------
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+        0
+(10 rows)
+
+SELECT  thousand
+		FROM onek WHERE thousand < 5
+		ORDER BY thousand FETCH FIRST 2 ROW ONLY;
+ thousand 
+----------
+        0
+        0
+(2 rows)
+
+-- should fail
+SELECT ''::text AS two, unique1, unique2, stringu1
+		FROM onek WHERE unique1 > 50
+		FETCH FIRST 2 ROW WITH TIES;
+ERROR:  WITH TIES options can not be specified without ORDER BY clause
+-- test ruleutils
+CREATE VIEW limit_thousand_v_1 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST 5 ROWS WITH TIES OFFSET 10;
+\d+ limit_thousand_v_1
+                      View "public.limit_thousand_v_1"
+  Column  |  Type   | Collation | Nullable | Default | Storage | Description 
+----------+---------+-----------+----------+---------+---------+-------------
+ thousand | integer |           |          |         | plain   | 
+View definition:
+ SELECT onek.thousand
+   FROM onek
+  WHERE onek.thousand < 995
+  ORDER BY onek.thousand
+ OFFSET 10
+ FETCH FIRST 5 ROWS WITH TIES;
+
+CREATE VIEW limit_thousand_v_2 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand OFFSET 10 FETCH FIRST 5 ROWS ONLY;
+\d+ limit_thousand_v_2
+                      View "public.limit_thousand_v_2"
+  Column  |  Type   | Collation | Nullable | Default | Storage | Description 
+----------+---------+-----------+----------+---------+---------+-------------
+ thousand | integer |           |          |         | plain   | 
+View definition:
+ SELECT onek.thousand
+   FROM onek
+  WHERE onek.thousand < 995
+  ORDER BY onek.thousand
+ OFFSET 10
+ LIMIT 5;
+
+CREATE VIEW limit_thousand_v_3 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST NULL ROWS WITH TIES;		-- fails
+ERROR:  row count cannot be NULL in FETCH FIRST ... WITH TIES clause
+CREATE VIEW limit_thousand_v_3 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST (NULL+1) ROWS WITH TIES;
+\d+ limit_thousand_v_3
+                      View "public.limit_thousand_v_3"
+  Column  |  Type   | Collation | Nullable | Default | Storage | Description 
+----------+---------+-----------+----------+---------+---------+-------------
+ thousand | integer |           |          |         | plain   | 
+View definition:
+ SELECT onek.thousand
+   FROM onek
+  WHERE onek.thousand < 995
+  ORDER BY onek.thousand
+ FETCH FIRST (NULL::integer + 1) ROWS WITH TIES;
+
+CREATE VIEW limit_thousand_v_4 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST NULL ROWS ONLY;
+\d+ limit_thousand_v_4
+                      View "public.limit_thousand_v_4"
+  Column  |  Type   | Collation | Nullable | Default | Storage | Description 
+----------+---------+-----------+----------+---------+---------+-------------
+ thousand | integer |           |          |         | plain   | 
+View definition:
+ SELECT onek.thousand
+   FROM onek
+  WHERE onek.thousand < 995
+  ORDER BY onek.thousand
+ LIMIT ALL;
+
+-- leave these views
diff --git a/src/test/regress/sql/limit.sql b/src/test/regress/sql/limit.sql
index 2a313d80ca8..afce5019b26 100644
--- a/src/test/regress/sql/limit.sql
+++ b/src/test/regress/sql/limit.sql
@@ -71,6 +71,16 @@ fetch backward all in c4;
 fetch backward 1 in c4;
 fetch all in c4;
 
+declare c5 cursor for select * from int8_tbl order by q1 fetch first 2 rows with ties;
+fetch all in c5;
+fetch 1 in c5;
+fetch backward 1 in c5;
+fetch backward 1 in c5;
+fetch all in c5;
+fetch backward all in c5;
+fetch all in c5;
+fetch backward all in c5;
+
 rollback;
 
 -- Stress test for variable LIMIT in conjunction with bounded-heap sorting
@@ -141,3 +151,41 @@ select sum(tenthous) as s1, sum(tenthous) + random()*0 as s2
 
 select sum(tenthous) as s1, sum(tenthous) + random()*0 as s2
   from tenk1 group by thousand order by thousand limit 3;
+
+--
+-- FETCH FIRST
+-- Check the WITH TIES clause
+--
+
+SELECT  thousand
+		FROM onek WHERE thousand < 5
+		ORDER BY thousand FETCH FIRST 2 ROW WITH TIES;
+
+SELECT  thousand
+		FROM onek WHERE thousand < 5
+		ORDER BY thousand FETCH FIRST 1 ROW WITH TIES;
+
+SELECT  thousand
+		FROM onek WHERE thousand < 5
+		ORDER BY thousand FETCH FIRST 2 ROW ONLY;
+-- should fail
+SELECT ''::text AS two, unique1, unique2, stringu1
+		FROM onek WHERE unique1 > 50
+		FETCH FIRST 2 ROW WITH TIES;
+
+-- test ruleutils
+CREATE VIEW limit_thousand_v_1 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST 5 ROWS WITH TIES OFFSET 10;
+\d+ limit_thousand_v_1
+CREATE VIEW limit_thousand_v_2 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand OFFSET 10 FETCH FIRST 5 ROWS ONLY;
+\d+ limit_thousand_v_2
+CREATE VIEW limit_thousand_v_3 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST NULL ROWS WITH TIES;		-- fails
+CREATE VIEW limit_thousand_v_3 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST (NULL+1) ROWS WITH TIES;
+\d+ limit_thousand_v_3
+CREATE VIEW limit_thousand_v_4 AS SELECT thousand FROM onek WHERE thousand < 995
+		ORDER BY thousand FETCH FIRST NULL ROWS ONLY;
+\d+ limit_thousand_v_4
+-- leave these views