func (from From) MergeClause(clause *Clause) {
	clause.Expression = from
}
MergeClause merge from clause
package clause
type From struct {
	Tables []Table
	Joins  []Join
}
func (from From) Name() string {
	return "FROM"
}
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)
	}
}