在MySQL中按首字母选择最大数量组

Question

I have column say, Process in MySQL table with values like A1,A2,..A100, B5,B7..B700, C2,C3...C900 each in separate row. I want to find max number from each initial. so output will be as

A100, B700,C900

I am using below query

select MAX(process) as max_process
from tablename
group by substr(process,1,1)

but it don't gives me max number

Answer 1

You can try below -

select MAX(cast(substr(process,2,length(process)-1) as signed)) as max_process
from tablename
group by substr(process,1,1)

Answer 2

Try:

select prefix, max(number) `max` from (
  select substring(process, 1, 1) prefix,
         cast(substring(process, 2, 100) as signed) number
  from MyTable
) a group by prefix;

Demo

Answer 3

You get the 1st char of process with left(process, 1) and the numeric part with substring(process, 2) .
Then by simply adding 0 to the numeric part you convert it to a number:

select
  left(process, 1) process1, 
  max(substring(process, 2) + 0) max_process
from tablename
group by process1