Add temporal PRIMARY KEY and UNIQUE constraints

Add WITHOUT OVERLAPS clause to PRIMARY KEY and UNIQUE constraints.
These are backed by GiST indexes instead of B-tree indexes, since they
are essentially exclusion constraints with = for the scalar parts of
the key and && for the temporal part.

(previously committed as 46a0cd4cefb, reverted by 46a0cd4cefb; the new
part is this:)

Because 'empty' && 'empty' is false, the temporal PK/UQ constraint
allowed duplicates, which is confusing to users and breaks internal
expectations.  For instance, when GROUP BY checks functional
dependencies on the PK, it allows selecting other columns from the
table, but in the presence of duplicate keys you could get the value
from any of their rows.  So we need to forbid empties.

This all means that at the moment we can only support ranges and
multiranges for temporal PK/UQs, unlike the original patch (above).
Documentation and tests for this are added.  But this could
conceivably be extended by introducing some more general support for
the notion of "empty" for other types.

Author: Paul A. Jungwirth <pj@illuminatedcomputing.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: jian he <jian.universality@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CA+renyUApHgSZF9-nd-a0+OPGharLQLO=mDHcY4_qQ0+noCUVg@mail.gmail.com

4 files changed, 71 insertions, 1 deletions

diff --git a/contrib/btree_gist/Makefile b/contrib/btree_gist/Makefile
index 9ab8548bc0e..7ac2df26c10 100644
--- a/contrib/btree_gist/Makefile
+++ b/contrib/btree_gist/Makefile
@@ -40,7 +40,7 @@ PGFILEDESC = "btree_gist - B-tree equivalent GiST operator classes"
 REGRESS = init int2 int4 int8 float4 float8 cash oid timestamp timestamptz \
         time timetz date interval macaddr macaddr8 inet cidr text varchar char \
         bytea bit varbit numeric uuid not_equal enum bool partitions \
-        stratnum
+        stratnum without_overlaps
 
 SHLIB_LINK += $(filter -lm, $(LIBS))
 
diff --git a/contrib/btree_gist/expected/without_overlaps.out b/contrib/btree_gist/expected/without_overlaps.out
new file mode 100644
index 00000000000..be52c522e89
--- /dev/null
+++ b/contrib/btree_gist/expected/without_overlaps.out
@@ -0,0 +1,44 @@
+-- Core must test WITHOUT OVERLAPS
+-- with an int4range + daterange,
+-- so here we do some simple tests
+-- to make sure int + daterange works too,
+-- since that is the expected use-case.
+CREATE TABLE temporal_rng (
+  id integer,
+  valid_at daterange,
+  CONSTRAINT temporal_rng_pk PRIMARY KEY (id, valid_at WITHOUT OVERLAPS)
+);
+\d temporal_rng
+              Table "public.temporal_rng"
+  Column  |   Type    | Collation | Nullable | Default 
+----------+-----------+-----------+----------+---------
+ id       | integer   |           | not null | 
+ valid_at | daterange |           | not null | 
+Indexes:
+    "temporal_rng_pk" PRIMARY KEY (id, valid_at WITHOUT OVERLAPS)
+
+SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conname = 'temporal_rng_pk';
+            pg_get_constraintdef             
+---------------------------------------------
+ PRIMARY KEY (id, valid_at WITHOUT OVERLAPS)
+(1 row)
+
+SELECT pg_get_indexdef(conindid, 0, true) FROM pg_constraint WHERE conname = 'temporal_rng_pk';
+                                pg_get_indexdef                                
+-------------------------------------------------------------------------------
+ CREATE UNIQUE INDEX temporal_rng_pk ON temporal_rng USING gist (id, valid_at)
+(1 row)
+
+INSERT INTO temporal_rng VALUES
+  (1, '[2000-01-01,2001-01-01)');
+-- same key, doesn't overlap:
+INSERT INTO temporal_rng VALUES
+  (1, '[2001-01-01,2002-01-01)');
+-- overlaps but different key:
+INSERT INTO temporal_rng VALUES
+  (2, '[2000-01-01,2001-01-01)');
+-- should fail:
+INSERT INTO temporal_rng VALUES
+  (1, '[2000-06-01,2001-01-01)');
+ERROR:  conflicting key value violates exclusion constraint "temporal_rng_pk"
+DETAIL:  Key (id, valid_at)=(1, [06-01-2000,01-01-2001)) conflicts with existing key (id, valid_at)=(1, [01-01-2000,01-01-2001)).
diff --git a/contrib/btree_gist/meson.build b/contrib/btree_gist/meson.build
index a44ce905e59..73b1bbf52a6 100644
--- a/contrib/btree_gist/meson.build
+++ b/contrib/btree_gist/meson.build
@@ -91,6 +91,7 @@ tests += {
       'bool',
       'partitions',
       'stratnum',
+      'without_overlaps',
     ],
   },
 }
diff --git a/contrib/btree_gist/sql/without_overlaps.sql b/contrib/btree_gist/sql/without_overlaps.sql
new file mode 100644
index 00000000000..433c609ab22
--- /dev/null
+++ b/contrib/btree_gist/sql/without_overlaps.sql
@@ -0,0 +1,25 @@
+-- Core must test WITHOUT OVERLAPS
+-- with an int4range + daterange,
+-- so here we do some simple tests
+-- to make sure int + daterange works too,
+-- since that is the expected use-case.
+CREATE TABLE temporal_rng (
+  id integer,
+  valid_at daterange,
+  CONSTRAINT temporal_rng_pk PRIMARY KEY (id, valid_at WITHOUT OVERLAPS)
+);
+\d temporal_rng
+SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conname = 'temporal_rng_pk';
+SELECT pg_get_indexdef(conindid, 0, true) FROM pg_constraint WHERE conname = 'temporal_rng_pk';
+
+INSERT INTO temporal_rng VALUES
+  (1, '[2000-01-01,2001-01-01)');
+-- same key, doesn't overlap:
+INSERT INTO temporal_rng VALUES
+  (1, '[2001-01-01,2002-01-01)');
+-- overlaps but different key:
+INSERT INTO temporal_rng VALUES
+  (2, '[2000-01-01,2001-01-01)');
+-- should fail:
+INSERT INTO temporal_rng VALUES
+  (1, '[2000-06-01,2001-01-01)');