Coalesce array of integers in Hive - hive

Question

foo_ids is an array of type bigint, but the entire array could be null. If the array is null, I want an empty array instead.
If I do this: COALESCE(foo_ids, ARRAY())
I get:
FAILED: SemanticException [Error 10016]: Line 13:45 Argument type mismatch 'ARRAY': The expressions after COALESCE should all have the same type: "array<bigint>" is expected but "array<string>" is found
If I do this: COALESCE(foo_ids, ARRAY<BIGINT>())
I get a syntax error: FAILED: ParseException line 13:59 cannot recognize input near ')' ')' 'AS' in expression specification
What's the proper syntax here?

Answer 1

Use this one:
coalesce(foo_ids, array(cast(null as bigint)))
Before, hive is treating empty array [] as []. But in Hadoop2, hive is now showing empty array [] as null (see refence below). Use array(cast(null as bigint)) for empty array of type bigint. Strangely, the size of empty array is -1 (instead of 0). Hope this helps. Thanks.
Sample data:
foo_ids
[112345677899098765,1123456778990987633]
[null,null]
NULL
select foo_ids, size(foo_ids) as sz from tbl;
Result:
foo_ids sz
[112345677899098765,1123456778990987633] 2
[null,null] 2
NULL -1
select foo_ids, coalesce(foo_ids, array(cast(null as bigint))) as newfoo from tbl;
Result:
foo_ids newfoo
[112345677899098765,1123456778990987633] [112345677899098765,1123456778990987633]
[null,null] [null,null]
NULL NULL
Reference: https://docs.treasuredata.com/articles/hive-change-201602