support insert DEFAULT VALUES (#981)

Author: jycor

server/ast/insert.go

@@ -89,8 +89,14 @@ func nodeInsert(ctx *Context, node *tree.Insert) (*vitess.Insert, error) {
 	if vSelect, ok := rows.(*vitess.Select); ok && len(vSelect.From) == 1 {
 		if aliasedStmt, ok := vSelect.From[0].(*vitess.AliasedTableExpr); ok {
 			if valsStmt, ok := aliasedStmt.Expr.(*vitess.ValuesStatement); ok {
+				var vals vitess.Values
+				if len(valsStmt.Rows) == 0 {
+					vals = []vitess.ValTuple{{}}
+				} else {
+					vals = valsStmt.Rows
+				}
 				rows = &vitess.AliasedValues{
-					Values: valsStmt.Rows,
+					Values: vals,
 				}
 			}
 		}

server/ast/select.go

@@ -30,7 +30,9 @@ func nodeSelect(ctx *Context, node *tree.Select) (vitess.SelectStatement, error)
 		return nil, nil
 	}
 	if node.Select == nil {
-		return nil, fmt.Errorf("internal: select clause should not be null")
+		node.Select = &tree.ValuesClause{
+			Rows: []tree.Exprs{},
+		}
 	}
 	selectStmt, err := nodeSelectStatement(ctx, node.Select)
 	if err != nil {

testing/go/insert_test.go

@@ -150,5 +150,23 @@ func TestInsert(t *testing.T) {
 				},
 			},
 		},
+		{
+			Name: "implicit default values",
+			SetUpScript: []string{
+				"CREATE TABLE t (i INT DEFAULT 123, j INT default 456);",
+			},
+			Assertions: []ScriptTestAssertion{
+				{
+					Query:            "INSERT INTO t DEFAULT VALUES;",
+					SkipResultsCheck: true,
+				},
+				{
+					Query: "SELECT * FROM t",
+					Expected: []sql.Row{
+						{123, 456},
+					},
+				},
+			},
+		},
 	})
 }