opt: make FK ON UPDATE CASCADE input columns anonymous

This commit anonymizes the columns in the input of a foreign key
ON UPDATE CASCADE expression. This is safe because these columns can
only be referenced by other expressions if they are update columns, and
in that case, `mutationBuilder.addUpdateCascade` will give them a
distinct name in the scope it produces. This change allows a special
case added in cockroachdb#57153 to be removed, without failing the regression test.

Release note: None

pkg/sql/opt/optbuilder/fk_cascade.go

@@ -677,10 +677,6 @@ func (cb *onUpdateCascadeBuilder) Build(
 			updateExprs[i] = &tree.UpdateExpr{}
 			switch cb.action {
 			case tree.Cascade:
-				// TODO(radu): This requires special code in addUpdateCols to
-				// prevent this scopeColumn from being duplicated in mb.outScope
-				// (see the addCol anonymous function in addUpdateCols). Find a
-				// cleaner way to handle this.
 				updateExprs[i].Expr = &newValScopeCols[i]
 			case tree.SetNull:
 				updateExprs[i].Expr = tree.DNull
@@ -871,12 +867,17 @@ func (b *Builder) buildUpdateCascadeMutationInput(
 		outScope.expr, mutationInput, on, memo.EmptyJoinPrivate,
 	)
 	// Append the columns from the right-hand side to the scope.
-	for i, col := range outCols {
+	//
+	// These columns can only be referenced if they are update columns. In that
+	// case, they are given distinct names in mutationBuilder.addUpdateCol, so
+	// we make them anonymous here. This prevents column name ambiguity in
+	// outScope. There is no need to attach a metadata name here because these
+	// columns have already been added to the metadata with a name in the calls
+	// to md.AddColumn above.
+	for _, col := range outCols {
 		colMeta := md.ColumnMeta(col)
-		ord := fk.OriginColumnOrdinal(childTable, i%numFKCols)
-		c := childTable.Column(ord)
 		outScope.cols = append(outScope.cols, scopeColumn{
-			name: scopeColName(c.ColName()),
+			name: scopeColName(""),
 			id:   col,
 			typ:  colMeta.Type,
 		})

pkg/sql/opt/optbuilder/update.go

@@ -212,21 +212,6 @@ func (mb *mutationBuilder) addUpdateCols(exprs tree.UpdateExprs) {
 	}
 
 	addCol := func(expr tree.Expr, targetColID opt.ColumnID) {
-		// If the expression is already a scopeColumn, we can skip creating a
-		// new scopeColumn and proceed with type checking and adding the column
-		// to the list of source columns to update. The expression can be a
-		// scopeColumn when addUpdateCols is called from the
-		// onUpdateCascadeBuilder while building foreign key cascading updates.
-		//
-		// The input scopeColumn is a pointer to a column in mb.outScope. It was
-		// copied by value to projectionsScope. The checkCol function mutates
-		// the name of projected columns, so we must lookup the column in
-		// projectionsScope so that the correct scopeColumn is renamed.
-		if scopeCol, ok := expr.(*scopeColumn); ok {
-			checkCol(projectionsScope.getColumn(scopeCol.id), targetColID)
-			return
-		}
-
 		// Allow right side of SET to be DEFAULT.
 		if _, ok := expr.(tree.DefaultVal); ok {
 			expr = mb.parseDefaultExpr(targetColID)