Allow ALTER TABLE ADD COLUMN to specify an inline FK constraint

server/ast/alter_table.go

@@ -98,6 +98,22 @@ func nodeAlterTableCmds(
 				return nil, nil, err
 			}
 			vitessDdlCmds = append(vitessDdlCmds, statement)
+
+			// Postgres (unlike MySQL) allows an inline FK constraint
+			// when altering a table to add a column. GMS doesn't support
+			// this directly in the ALTER TABLE ADD COLUMN DDL command,
+			// so we break this out into a separate DDL command.
+			if len(statement.TableSpec.Constraints) > 0 {
+				vitessDdlCmds = append(vitessDdlCmds,
+					&vitess.DDL{
+						Action:           "alter",
+						ConstraintAction: "add",
+						Table:            tableName,
+						IfExists:         ifExists,
+						TableSpec:        statement.TableSpec,
+					})
+			}
+
 		case *tree.AlterTableDropColumn:
 			statement, err = nodeAlterTableDropColumn(ctx, cmd, tableName, ifExists)
 			if err != nil {
@@ -217,6 +233,14 @@ func nodeAlterTableAddColumn(ctx *Context, node *tree.AlterTableAddColumn, table
 	tableSpec := &vitess.TableSpec{}
 	tableSpec.AddColumn(vitessColumnDef)
 
+	if node.ColumnDef.References.Table != nil {
+		constraintDef, err := nodeForeignKeyDefinitionFromColumnTableDef(ctx, node.ColumnDef.Name, node.ColumnDef)
+		if err != nil {
+			return nil, err
+		}
+		tableSpec.AddConstraint(&vitess.ConstraintDefinition{Details: constraintDef})
+	}
+
 	return &vitess.DDL{
 		Action:       "alter",
 		ColumnAction: "add",

testing/go/alter_table_test.go

@@ -491,6 +491,27 @@ func TestAlterTable(t *testing.T) {
 				},
 			},
 		},
+		{
+			Name: "ALTER TABLE ADD COLUMN with inline FK constraint",
+			SetUpScript: []string{
+				"create table t (v varchar(100));",
+				"create table parent (id int primary key);",
+			},
+			Assertions: []ScriptTestAssertion{
+				{
+					Query:    "ALTER TABLE t ADD COLUMN c1 int REFERENCES parent(id);",
+					Expected: []sql.Row{},
+				},
+				{
+					Query:    "SELECT conname AS constraint_name, pg_get_constraintdef(oid) AS constraint_definition FROM pg_constraint WHERE conrelid = 't'::regclass AND contype='f';",
+					Expected: []sql.Row{{"t_c1_fkey", "FOREIGN KEY t_c1_fkey (c1) REFERENCES parent (id)"}},
+				},
+				{
+					Query:       "INSERT INTO t VALUES ('abc', 123);",
+					ExpectedErr: "Foreign key violation on fk: `t_c1_fkey`",
+				},
+			},
+		},
 		{
 			Name: "Rename table",
 			SetUpScript: []string{