[DRILL-3806] add metadata for untyped null and simple type promotion

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Fix Version/s: Future
• Component/s: Execution - Data Types
• Assignee: Unassigned
• Reporter: Julien Le Dem
• Created: 18/Sep/15 22:23
• Updated: 12/Jun/17 10:54

Description

Currently when a field has literal null values in JSON the type will be assigned as BIGINT by default for lack of better type.
```
{
"a": null
}
```
if later on a is assigned with a string value the query will fail with a schema change error,

The idea is to capture the notion of "untyped null" and implement simple type promotion from untyped null to the actual type.

Issue Links

• relates to: DRILL-3577 Counting nested fields on CTAS-created-parquet file/s reports inaccurate results
• relates to: DRILL-4479 JsonReader should pick a less restrictive type when creating the default column
• relates to: DRILL-4614 Drill must appoint one data type per one column for self-describing data while querying directories
• relates to: DRILL-4824 Null maps / lists and non-provided state support for JSON fields. Numeric types promotion.