Add temporal FOREIGN KEY contraints

Add PERIOD clause to foreign key constraint definitions.  This is
supported for range and multirange types.  Temporal foreign keys check
for range containment instead of equality.

This feature matches the behavior of the SQL standard temporal foreign
keys, but it works on PostgreSQL's native ranges instead of SQL's
"periods", which don't exist in PostgreSQL (yet).

Reference actions ON {UPDATE,DELETE} {CASCADE,SET NULL,SET DEFAULT}
are not supported yet.

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

1 files changed, 58 insertions, 0 deletions

diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index f1543ae7d35..604280d322e 100644
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -15,6 +15,7 @@
 #include "postgres.h"
 
 #include "access/genam.h"
+#include "access/gist.h"
 #include "access/htup_details.h"
 #include "access/sysattr.h"
 #include "access/table.h"
@@ -1650,6 +1651,63 @@ DeconstructFkConstraintRow(HeapTuple tuple, int *numfks,
 }
 
 /*
+ * FindFkPeriodOpers -
+ *
+ * Looks up the operator oids used for the PERIOD part of a temporal foreign key.
+ * The opclass should be the opclass of that PERIOD element.
+ * Everything else is an output: containedbyoperoid is the ContainedBy operator for
+ * types matching the PERIOD element.
+ * aggedcontainedbyoperoid is also a ContainedBy operator,
+ * but one whose rhs is a multirange.
+ * That way foreign keys can compare fkattr <@ range_agg(pkattr).
+ */
+void
+FindFKPeriodOpers(Oid opclass,
+				  Oid *containedbyoperoid,
+				  Oid *aggedcontainedbyoperoid)
+{
+	Oid			opfamily = InvalidOid;
+	Oid			opcintype = InvalidOid;
+	StrategyNumber strat;
+
+	/* Make sure we have a range or multirange. */
+	if (get_opclass_opfamily_and_input_type(opclass, &opfamily, &opcintype))
+	{
+		if (opcintype != ANYRANGEOID && opcintype != ANYMULTIRANGEOID)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("invalid type for PERIOD part of foreign key"),
+					errdetail("Only range and multirange are supported."));
+
+	}
+	else
+		elog(ERROR, "cache lookup failed for opclass %u", opclass);
+
+	/*
+	 * Look up the ContainedBy operator whose lhs and rhs are the opclass's
+	 * type. We use this to optimize RI checks: if the new value includes all
+	 * of the old value, then we can treat the attribute as if it didn't
+	 * change, and skip the RI check.
+	 */
+	strat = RTContainedByStrategyNumber;
+	GetOperatorFromWellKnownStrategy(opclass,
+									 InvalidOid,
+									 containedbyoperoid,
+									 &strat);
+
+	/*
+	 * Now look up the ContainedBy operator. Its left arg must be the type of
+	 * the column (or rather of the opclass). Its right arg must match the
+	 * return type of the support proc.
+	 */
+	strat = RTContainedByStrategyNumber;
+	GetOperatorFromWellKnownStrategy(opclass,
+									 ANYMULTIRANGEOID,
+									 aggedcontainedbyoperoid,
+									 &strat);
+}
+
+/*
  * Determine whether a relation can be proven functionally dependent on
  * a set of grouping columns.  If so, return true and add the pg_constraint
  * OIDs of the constraints needed for the proof to the *constraintDeps list.