SQL选择最大值

Question

例如，在myValue列中有值'X'，'Y'，'Z'，''

并想做类似选择max（myValue）

所以我想要一个值，其中X = 1，Y = 2和Z = 0的值最大

Answer 1

select max(
    case myValue
        when 'X' then 1
        when 'Y' then 2
        when 'Z' then 0
    end) myValue
from myTable

Answer 2

(select max(PurDate) as mb,prodid as pd
from batch group by ProdId ) as rs 
on p.RndId = b.ProdId 
and p.ComId = c.RndId
where b.PurDate = rs.mb 
and b.ProdId = rs.pd 
and p.RndId in (select distinct prodid 
                from TranItem as ci, TranMain 
                as tm 
                where tm.RndId = ci.TranId 
                and tm.Invdate between '2016-May-01' and '2016-May-31')