Combining two columns into a single map column in hive table

Question

I have a hive table like

    a   b  
-------------
    1   2
    3   4

How can I create a map column c

     c
-----------
    1: 2
    3: 4

where column a is the keys and column b is the values?

Answer 1

Use map() construct in Hive:

select map(a,b) as c from mytable

In Presto you can use map(array[key], array[value])

select map(array[a],array[b]) as c from mytable

Or map_agg()

select map_agg(a,b) as c from mytable group by a,b