[英]NULL in sql case when statements
我将按年龄将人们按年龄分类,并带有case when
语句,因此
select
case when age >= 11 and age <= 20 then name end column1 as "11-20",
case when age >= 21 and age <= 30 then name end column2 as "21-30",
case when age >= 31 and age <= 40 then name end column3 as "31-40"
from passenger
结果是这样的:
11-20 21-30 31-40
John NULL NULL
NULL Kevin NULL
Michael NULL NULL
NULL NULL Beckey
我希望输出看起来像:
11-20 21-30 31-40
John Kevin Beckey
Michael
所以我该如何删除NULL或将非NULL值向上移动?
根据戈登·林多夫(Gordon Lindoff)的Oracle(?)答案,您可以在MySQL中执行以下操作:
select
max(case when agegroup = '11-20' then name end) as "11-20",
max(case when agegroup = '21-30' then name end) as "21-30",
max(case when agegroup = '31-40' then name end) as "31-40"
from
(select @rownum1 := 0, @rownum2 := 0, @rownum3 := 0) v,
(select
case
when Age > 10 and Age <= 20 then '11-20'
when Age > 20 and Age <= 30 then '21-30'
when Age > 30 and Age <= 40 then '31-40'
end as agegroup,
case
when Age > 10 and Age <= 20 then @rownum1 := @rownum1 + 1
when Age > 20 and Age <= 30 then @rownum2 := @rownum2 + 1
when Age > 30 and Age <= 40 then @rownum3 := @rownum3 + 1
end as seqnum,
name
from
Passengers) p
group by
seqnum
演示: http : //sqlfiddle.com/#!2/5ea1a/9
摆弄给定的数据。
通过对group by
进行group by
可以删除NULL
。 但是,您没有group by
的密钥。 大多数数据库都支持row_number()
函数。 使用该功能,您可以执行以下操作:
select max(case when agegroup = '11-20' then name end) as "11-20",
max(case when agegroup = '21-30' then name end) as "21-30",
max(case when agegroup = '31-40' then name end) as "31-40"
from (select p.*, row_number() over (partition by agegroup order by name) as seqnum
from (select p.*,
(case when age >= 11 and age <= 20 then '11-20'
when age >= 21 and age <= 30 then '21-30'
when age >= 31 and age <= 40 then '31-40'
end) as agegroup
from passenger p
) p
group by seqnum;
编辑:
MySQL中的等效项使用变量:
select max(case when agegroup = '11-20' then name end) as "11-20",
max(case when agegroup = '21-30' then name end) as "21-30",
max(case when agegroup = '31-40' then name end) as "31-40"
from (select p.*,
@rn := if(agegroup = @agegroup, @rn + 1, 1) as seqnum,
@agegroup := agegroup
from (select p.*,
(case when age >= 11 and age <= 20 then '11-20'
when age >= 21 and age <= 30 then '21-30'
when age >= 31 and age <= 40 then '31-40'
end) as agegroup
from passenger p
) p cross join
(select @rn := 0, @agegroup := '') var
order by agegroup
) p
group by seqnum;
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