sql: disallow virtual columns in FK references

Disallow FK references to or from virtual columns. Note that there is
no big reason why we couldn't support them other than some extra work
and testing surface; this is tracked by cockroachdb#59671.

Informs cockroachdb#57608.

Release note: None

pkg/sql/alter_table.go

@@ -300,16 +300,6 @@ func (n *alterTableNode) startExec(params runParams) error {
 				}
 
 			case *tree.ForeignKeyConstraintTableDef:
-				for _, colName := range d.FromCols {
-					col, err := n.tableDesc.FindActiveOrNewColumnByName(colName)
-					if err != nil {
-						return err
-					}
-
-					if err := col.CheckCanBeFKRef(); err != nil {
-						return err
-					}
-				}
 				affected := make(map[descpb.ID]*tabledesc.Mutable)
 
 				// If there are any FKs, we will need to update the table descriptor of the

pkg/sql/catalog/descpb/column.go

@@ -45,11 +45,30 @@ func (desc *ColumnDescriptor) ColName() tree.Name {
 	return tree.Name(desc.Name)
 }
 
-// CheckCanBeFKRef returns whether the given column is computed.
-func (desc *ColumnDescriptor) CheckCanBeFKRef() error {
+// CheckCanBeOutboundFKRef returns whether the given column can be on the
+// referencing (origin) side of a foreign key relation.
+func (desc *ColumnDescriptor) CheckCanBeOutboundFKRef() error {
+	if desc.Virtual {
+		return unimplemented.NewWithIssuef(
+			59671, "virtual column %q cannot reference a foreign key",
+			desc.Name,
+		)
+	}
 	if desc.IsComputed() {
 		return unimplemented.NewWithIssuef(
-			46672, "computed column %q cannot be a foreign key reference",
+			46672, "computed column %q cannot reference a foreign key",
+			desc.Name,
+		)
+	}
+	return nil
+}
+
+// CheckCanBeInboundFKRef returns whether the given column can be on the
+// referenced (target) side of a foreign key relation.
+func (desc *ColumnDescriptor) CheckCanBeInboundFKRef() error {
+	if desc.Virtual {
+		return unimplemented.NewWithIssuef(
+			59671, "virtual column %q cannot be referenced by a foreign key",
 			desc.Name,
 		)
 	}

pkg/sql/create_table.go

@@ -809,7 +809,7 @@ func ResolveFK(
 		if err != nil {
 			return err
 		}
-		if err := col.CheckCanBeFKRef(); err != nil {
+		if err := col.CheckCanBeOutboundFKRef(); err != nil {
 			return err
 		}
 		// Ensure that the origin columns don't have duplicates.
@@ -883,6 +883,12 @@ func ResolveFK(
 		return err
 	}
 
+	for i := range referencedCols {
+		if err := referencedCols[i].CheckCanBeInboundFKRef(); err != nil {
+			return err
+		}
+	}
+
 	if len(referencedCols) != len(originCols) {
 		return pgerror.Newf(pgcode.Syntax,
 			"%d columns must reference exactly %d columns in referenced table (found %d)",

pkg/sql/logictest/testdata/logic_test/computed

@@ -358,17 +358,17 @@ CREATE TABLE y (
   r INT AS (q) STORED
 )
 
-statement error computed column "r" cannot be a foreign key reference
+statement error computed column "r" cannot reference a foreign key
 CREATE TABLE y (
   r INT AS (1) STORED REFERENCES x (a)
 )
 
-statement error computed column "r" cannot be a foreign key reference
+statement error computed column "r" cannot reference a foreign key
 CREATE TABLE y (
   r INT AS (1) STORED REFERENCES x
 )
 
-statement error computed column "r" cannot be a foreign key reference
+statement error computed column "r" cannot reference a foreign key
 CREATE TABLE y (
   a INT,
   r INT AS (1) STORED REFERENCES x
@@ -393,14 +393,14 @@ CREATE TABLE xx (
   UNIQUE (a, b)
 )
 
-statement error computed column "y" cannot be a foreign key reference
+statement error computed column "y" cannot reference a foreign key
 CREATE TABLE yy (
   x INT,
   y INT AS (3) STORED,
   FOREIGN KEY (x, y) REFERENCES xx (a, b)
 )
 
-statement error computed column "y" cannot be a foreign key reference
+statement error computed column "y" cannot reference a foreign key
 CREATE TABLE yy (
   x INT,
   y INT AS (3) STORED,
@@ -416,7 +416,7 @@ CREATE TABLE y (
   INDEX (r)
 )
 
-statement error computed column "r" cannot be a foreign key reference
+statement error computed column "r" cannot reference a foreign key
 ALTER TABLE y ADD FOREIGN KEY (r) REFERENCES x (a)
 
 statement ok

pkg/sql/logictest/testdata/logic_test/virtual_columns

@@ -500,3 +500,45 @@ a  b   v   w1  w2
 1  10  11  10  20
 2  20  22  40  40
 3  30  33  90  60
+
+# Verify that FK relations on virtual columns are disallowed.
+statement ok
+CREATE TABLE fk (
+  a INT PRIMARY KEY,
+  b INT,
+  c INT,
+  u INT UNIQUE AS (b+c) VIRTUAL
+)
+
+statement error virtual column "u" cannot be referenced by a foreign key
+CREATE TABLE fk2 (
+  p INT PRIMARY KEY,
+  c INT REFERENCES fk(u)
+)
+
+statement error virtual column "c" cannot reference a foreign key
+CREATE TABLE fk2 (
+  p INT PRIMARY KEY,
+  c INT AS (p+1) VIRTUAL REFERENCES fk(a)
+)
+
+statement error virtual column "u" cannot be referenced by a foreign key
+CREATE TABLE fk2 (
+  p INT PRIMARY KEY,
+  q INT,
+  r INT,
+  CONSTRAINT fk FOREIGN KEY (q,r) REFERENCES fk(a,u)
+)
+
+statement ok
+CREATE TABLE fk2 (
+  x INT PRIMARY KEY,
+  y INT,
+  v INT AS (x+y) VIRTUAL
+)
+
+statement error virtual column "u" cannot be referenced by a foreign key
+ALTER TABLE fk2 ADD CONSTRAINT foo FOREIGN KEY (x) REFERENCES fk(u)
+
+statement error virtual column "v" cannot reference a foreign key
+ALTER TABLE fk2 ADD CONSTRAINT foo FOREIGN KEY (v) REFERENCES fk(a)