ETL_场景练习
1 行列转换
(1) 列拆分为多行
把指定字段按指定分隔符进行拆分为多行,然后其它字段直接复制.
select字段列,hobby2
from tbl
-- lateral view udtf(expression) tablealias as columnalias (‘,’ columnalias)
lateral view explode(split(hobby,';')) temp as hobby2(2) 行扁平化
把同一组的多行数据合并成为一行.
select id, name, age, split(concat_ws(':',collect_list(hobby)),':')[0] as hobby1,split(concat_ws(':',collect_list(hobby)),':')[1] as hobby2,split(concat_ws(':',collect_list(hobby)),':')[2] as hobby3
from tbl
group by id, name, age;(3) 列转行
如果数据一列有相同的值，按照指定的字段，将其中一列的字段内容变成不同的列，然后把多行数据转换为一行数据.
selectname,max(if(wek = '周一',work_hour,0)) as mon,max(if(wek = '周二',work_hour,0)) as tue,max(if(wek = '周三',work_hour,0)) as wed,max(if(wek = '周四',work_hour,0)) as thu,max(if(wek = '周五',work_hour,0)) as fi,max(if(wek = '周六',work_hour,0)) as sat,max(if(wek = '周日',work_hour,0)) as sun
from tbl
group by name(4) 行转列
把数据字段的字段名转换为一列，把数据行变为数据列.
select name, 'mon' as wek, mon as work_hour from tbl
union all
select name, 'tue' as wek, tue as work_hour from tbl
union all
select name, 'wed' as wek, wed as work_hour from tbl
union all
select name, 'thu' as wek, thu as work_hour from tbl
union all
select name, 'fri' as wek, fri as work_hour from tbl
union all
select name, 'sat' as wek, sat as work_hour from tbl
union all
select name, 'sun' as wek, sun as work_hour from tbl