hvordan man giver samme serienummer for en gruppe af poster i mysql

Dine grupper defineres ved at starte med code = 100 . Det her er lidt tricky. I MySQL 8+ kan du bruge vinduesfunktioner til at definere grupperne og derefter row_number() for at tildele serial_number :

select c.*, 
       row_number() over (partition by grp order by id) as serial_number
from (select c.*,
             sum( code = 100 ) over (order by id) as grp
      from carts c
     ) c;

Dette er meget mere kompliceret i tidligere versioner af MySQL.

Du kan identificere gruppen ved hjælp af en underforespørgsel:

select c.*,
       (select count(*)
        from carts c2
        where c2.id <= c.id and c2.code = 100
       ) as grp
from carts c;

Du kan derefter bruge variabler til at få den information, du ønsker:

select c.*,
       (@rn := if(@g = grp, @rn + 1,
                  if(@g := grp, 1, 1)
                 )
       ) as serial_number
from (select c.*,
             (select count(*)
              from carts c2
              where c2.id <= c.id and c2.code = 100
             ) as grp
      from carts c
      order by grp, id
     ) c cross join
     (select @g := -1, @rn := 0) params;