sql: disqualify partial unique indexes as foreign key reference indexes

Release justification: This is a critical bug fix for a new feature,
partial indexes.

Release note (bug fix): Foreign keys can no longer reference columns
that are only indexed by a partial unique index. A partial unique index
does not guarantee uniqueness in the entire table, therefore the column
indexed is not guaranteed to be a unique key.

pkg/sql/catalog/descpb/index.go

@@ -160,13 +160,13 @@ func (desc *IndexDescriptor) ColNamesString() string {
 // IsValidOriginIndex returns whether the index can serve as an origin index for a foreign
 // key constraint with the provided set of originColIDs.
 func (desc *IndexDescriptor) IsValidOriginIndex(originColIDs ColumnIDs) bool {
-	return ColumnIDs(desc.ColumnIDs).HasPrefix(originColIDs)
+	return !desc.IsPartial() && ColumnIDs(desc.ColumnIDs).HasPrefix(originColIDs)
 }
 
 // IsValidReferencedIndex returns whether the index can serve as a referenced index for a foreign
 // key constraint with the provided set of referencedColumnIDs.
 func (desc *IndexDescriptor) IsValidReferencedIndex(referencedColIDs ColumnIDs) bool {
-	return desc.Unique && ColumnIDs(desc.ColumnIDs).Equals(referencedColIDs)
+	return desc.Unique && !desc.IsPartial() && ColumnIDs(desc.ColumnIDs).Equals(referencedColIDs)
 }
 
 // HasOldStoredColumns returns whether the index has stored columns in the old

pkg/sql/logictest/testdata/logic_test/fk

@@ -3626,3 +3626,13 @@ USE db2
 
 statement ok
 CREATE TABLE child2 (c INT PRIMARY KEY, p INT REFERENCES db1.public.parent(p))
+
+# Test that foreign keys cannot reference columns that are indexed by a partial
+# unique index. Partial unique indexes do not guarantee uniqueness in the entire
+# table.
+
+statement ok
+CREATE TABLE partial_parent (p INT, UNIQUE INDEX (p) WHERE p > 100)
+
+statement error there is no unique constraint matching given keys for referenced table partial_parent
+CREATE TABLE partial_child (p INT REFERENCES partial_parent (p))

pkg/sql/opt/testutils/testcat/create_table.go

@@ -365,6 +365,9 @@ func (tc *Catalog) resolveFK(tab *Table, d *tree.ForeignKeyConstraintTableDef) {
 				return false
 			}
 		}
+		if _, isPartialIndex := idx.Predicate(); isPartialIndex {
+			return false
+		}
 		return true
 	}