Hadoop 使用数据验证合并配置单元中的两个表

我有两个具有类似列的表。说，

表X

具有

id、名、姓

表Y

有

id、电子邮件id、名字

但是，这两个表都不完善，因此我需要从另一个表中的数据（使用一些键（eg中的id））填充这两个表中的空值，并将其推送到另一个表中

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如何有效地执行此操作？

只需连接表，然后编写一个

case

语句

示例0：

select x.id as id
  , case when x.first_name is null then y.first_name else x.first_name end as first_name
  , x.last_name as last_name
  , y.email_id as email_id
from db.tableX x
join db.tableY y
on y.id = x.id

select x.id as id
  , if(x.first_name is null, y.first_name, x.first_name) as first_name
  , x.last_name as last_name
  , y.email_id as email_id
from db.tableX x
join db.tableY y
on y.id = x.id

或者，您也可以使用

if

语句执行大致相同的操作

示例1：

select x.id as id
  , case when x.first_name is null then y.first_name else x.first_name end as first_name
  , x.last_name as last_name
  , y.email_id as email_id
from db.tableX x
join db.tableY y
on y.id = x.id

select x.id as id
  , if(x.first_name is null, y.first_name, x.first_name) as first_name
  , x.last_name as last_name
  , y.email_id as email_id
from db.tableX x
join db.tableY y
on y.id = x.id