hadoop - Merging two tables in Hive with data validation -

i have 2 tables similar columns. say,
table x has id,first_name last_name.
table y has id,email_id, first_name.

however both these tables imperfect, need fill in null values in both tables data in other table(using key(id in eg)) , push table.

how can efficiently ?

just join tables , write case statement.

example 0:

select x.id id   , case when x.first_name null y.first_name else x.first_name end first_name   , x.last_name last_name   , y.email_id email_id db.tablex x join db.tabley y on y.id = x.id 

or pretty same if statement.

example 1:

select x.id id   , if(x.first_name null, y.first_name, x.first_name) first_name   , x.last_name last_name   , y.email_id email_id db.tablex x join db.tabley y on y.id = x.id