[ SQL ] เรื่องการ Count และการเช็คการอัพเดต

select count(type) from(
   select distinct type from table
) as tmp

select count(xtype) from(
   select distinct case type when 3 then 2 else type end as xtype from table
) as tmp

select count(xtype) from(
   select distinct 
   case type 
   when 3 then 2 
   when 5 then 4
   when 6 then 4
   else type 
   end as xtype from table
) as tmp

select count(*) 
from (
  select distinct g.id
  from ( 
   select 'A' as Name, 1 as Type union
   select 'B', 1 union
   select 'C', 1 union
   select 'D', 2 union
   select 'E', 2 union
   select 'F', 2 union
   select 'G', 2 union
   select 'H', 3 union
   select 'J', 3
  ) as d
  left join (
    select 1 as id, '1,2' as types union
    select 2, '3,4,5'
  ) as g 
  on find_in_set(d.type, g.types)
) as tmp