希望对一些字段求和,而忽略其他字段吗

select region, 
    case when repeatLength >= 18 then ">=18" else repeatLength end as repeatLength, 
    count(*) as count  
from alignedRepeats 
group by region, 
    case when repeatLength >= 18 then ">=18" else repeatLength end; 

select region, repeatLength, 1 as Colname
from alignedRepeats
where repeatLength < 18
union
select region, repeatLength, count(*)
from alignedRepeats
where repeatLength >= 18
group by region, repeatLength;

但不确定最后一个字段要包含什么,因此“1 as Colname”

正确答案(已测试)

select
    region,
    repeatLength,
    count(*) as count
from
    alignedRepeats
where
    repeatLength < 18
group by
    region,
    repeatLength
union
select
    region,
    999,
    count(*)
from
    alignedRepeats
where
    repeatLength >= 18
group by
    region

注:用“999”表示聚合行。