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

	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{}) {

type Gt Eq

func (gt Gt) Build(builder Builder) {
	builder.WriteQuoted(gt.Column)
	builder.WriteString(" > ")
	builder.AddVar(builder, gt.Value)
}

func (gt Gt) NegationBuild(builder Builder) {
	Lte(gt).Build(builder)
}

// Gte greater than or equal to for where
type Gte Eq

func (gte Gte) Build(builder Builder) {
	builder.WriteQuoted(gte.Column)
	builder.WriteString(" >= ")

func (from From) Build(builder Builder) {
	if len(from.Tables) > 0 {
		for idx, table := range from.Tables {
			if idx > 0 {
				builder.WriteByte(',')
			}

			builder.WriteQuoted(table)
		}
	} else {
		builder.WriteQuoted(currentTable)
	}

	for _, join := range from.Joins {
		builder.WriteByte(' ')
		join.Build(builder)
	}
}

// MergeClause merge from clause

	if insert.Modifier != "" {
		builder.WriteString(insert.Modifier)
		builder.WriteByte(' ')
	}

	builder.WriteString("INTO ")
	if insert.Table.Name == "" {
		builder.WriteQuoted(currentTable)
	} else {
		builder.WriteQuoted(insert.Table)
	}
}

// MergeClause merge insert clause
func (insert Insert) MergeClause(clause *Clause) {
	if v, ok := clause.Expression.(Insert); ok {
		if insert.Modifier == "" {

	return "GROUP BY"
}

// Build build group by clause
func (groupBy GroupBy) Build(builder Builder) {
	for idx, column := range groupBy.Columns {
		if idx > 0 {
			builder.WriteByte(',')
		}

		builder.WriteQuoted(column)
	}

	if len(groupBy.Having) > 0 {
		builder.WriteString(" HAVING ")
		Where{Exprs: groupBy.Having}.Build(builder)
	}
}

// MergeClause merge group by clause

		for idx, assignment := range set {
			if idx > 0 {
				builder.WriteByte(',')
			}
			builder.WriteQuoted(assignment.Column)
			builder.WriteByte('=')
			builder.AddVar(builder, assignment.Value)
		}
	} else {
		builder.WriteQuoted(Column{Name: PrimaryKey})
		builder.WriteByte('=')
		builder.WriteQuoted(Column{Name: PrimaryKey})
	}
}

// MergeClause merge assignments clauses

		builder.WriteByte(' ')
	} else {
		if len(onConflict.Columns) > 0 {
			builder.WriteByte('(')
			for idx, column := range onConflict.Columns {
				if idx > 0 {
					builder.WriteByte(',')
				}
				builder.WriteQuoted(column)
			}
			builder.WriteString(`) `)
		}

		if len(onConflict.TargetWhere.Exprs) > 0 {
			builder.WriteString(" WHERE ")
			onConflict.TargetWhere.Build(builder)
			builder.WriteByte(' ')
		}
	}

func (update Update) Build(builder Builder) {
	if update.Modifier != "" {
		builder.WriteString(update.Modifier)
		builder.WriteByte(' ')
	}

	if update.Table.Name == "" {
		builder.WriteQuoted(currentTable)
	} else {
		builder.WriteQuoted(update.Table)
	}
}

// MergeClause merge update clause
func (update Update) MergeClause(clause *Clause) {
	if v, ok := clause.Expression.(Update); ok {
		if update.Modifier == "" {

	if orderBy.Expression != nil {
		orderBy.Expression.Build(builder)
	} else {
		for idx, column := range orderBy.Columns {
			if idx > 0 {
				builder.WriteByte(',')
			}

			builder.WriteQuoted(column.Column)
			if column.Desc {
				builder.WriteString(" DESC")
			}
		}
	}
}

// MergeClause merge order by clauses
func (orderBy OrderBy) MergeClause(clause *Clause) {