[HIVE-12028] An empty array is of type Array<String> and incompatible with other array types

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.1.0, 1.2.1
• Assignee: Unassigned
• Reporter: Furcy Pin
• Created: 03/Oct/15 18:30
• Updated: 14/Oct/15 08:51

Description

How to reproduce:

```sql
SELECT ARRAY(ARRAY(1),ARRAY()) ;
FAILED: SemanticException [Error 10016]: Line 1:22 Argument type mismatch 'ARRAY': Argument type "array<string>" is different from preceding arguments. Previous type was "array<int>"

SELECT COALESCE(ARRAY(1),ARRAY()) ;
FAILED: SemanticException [Error 10016]: Line 1:25 Argument type mismatch 'ARRAY': The expressions after COALESCE should all have the same type: "array<int>" is expected but "array<string>" is found
```

This is especially painful for COALESCE, as we cannot
remove NULLS after doing a JOIN.

The same problem holds with maps.

The only workaround I could think of (except adding my own UDF)
is quite ugly :

```sql
SELECT ARRAY(ARRAY(1),empty.arr) FROM (SELECT collect_set(id) as arr FROM (SELECT 1 as id) T WHERE id=0) empty ;
```