func (u *sqlUniter) Unit() (Unit, error) {
	return NewSQLUnit(u.mappers, u.db, u.options...)
}
Unit constructs a new SQL work unit.
package work
import "database/sql"
type sqlUniter struct {
	mappers map[TypeName]SQLDataMapper
	db      *sql.DB
	options []Option
}
func NewSQLUniter(
	mappers map[TypeName]SQLDataMapper,
	db *sql.DB,
	options ...Option,
) Uniter {
	return &sqlUniter{
		mappers: mappers,
		db:      db,
		options: options,
	}
}