func (returning Returning) Build(builder Builder) {
	if len(returning.Columns) > 0 {
		for idx, column := range returning.Columns {
			if idx > 0 {
				builder.WriteByte(',')
			}

			builder.WriteQuoted(column)
		}
	} else {
		builder.WriteByte('*')
	}
}

// MergeClause merge order by clauses
func (returning Returning) MergeClause(clause *Clause) {

type ClauseBuilder func(Clause, Builder)

type Writer interface {
	WriteByte(byte) error
	WriteString(string) (int, error)
}

// Builder builder interface
type Builder interface {
	Writer
	WriteQuoted(field interface{})
	AddVar(Writer, ...interface{})
	AddError(error) error
}

// Clause
type Clause struct {
	Name                string // WHERE
	BeforeExpression    Expression

func (values Values) Build(builder Builder) {
	if len(values.Columns) > 0 {
		builder.WriteByte('(')
		for idx, column := range values.Columns {
			if idx > 0 {
				builder.WriteByte(',')
			}
			builder.WriteQuoted(column)
		}
		builder.WriteByte(')')

		builder.WriteString(" VALUES ")

		for idx, value := range values.Values {
			if idx > 0 {
				builder.WriteByte(',')
			}

			builder.WriteByte('(')

	if len(s.Columns) > 0 {
		if s.Distinct {
			builder.WriteString("DISTINCT ")
		}

		for idx, column := range s.Columns {
			if idx > 0 {
				builder.WriteByte(',')
			}
			builder.WriteQuoted(column)
		}
	} else {
		builder.WriteByte('*')
	}
}

func (s Select) MergeClause(clause *Clause) {
	if s.Expression != nil {
		if s.Distinct {
			if expr, ok := s.Expression.(Expr); ok {

	return stmt.SQL.WriteString(str)
}

// WriteByte write byte
func (stmt *Statement) WriteByte(c byte) error {
	return stmt.SQL.WriteByte(c)
}

// WriteQuoted write quoted value
func (stmt *Statement) WriteQuoted(value interface{}) {
	stmt.QuoteTo(&stmt.SQL, value)
}

// QuoteTo write quoted value to writer
func (stmt *Statement) QuoteTo(writer clause.Writer, field interface{}) {