[DRILL-7426] Json support lists of different types

• Type: Improvement
• Status: Open
• Priority: Trivial
• Resolution: Unresolved
• Affects Version/s: 1.16.0
• Component/s: Documentation
• Assignee: Unassigned
• Reporter: benj
• Created: 28/Oct/19 16:39
• Updated: 29/Oct/19 08:33

Description

With a file.json like

{
    "name": "toto",
    "info": [["LOAD", []]],
    "response": 1
}

A simple SELECT gives an error

apache drill> SELECT * FROM dfs.test.`file.json`;
Error: UNSUPPORTED_OPERATION ERROR: In a list of type VARCHAR, encountered a value of type LIST. Drill does not support lists of different types.

But there is an option exec.enable_union_type that allows these request

apache drill> ALTER SESSION SET `exec.enable_union_type` = true;
apache drill> SELECT * FROM dfs.test.`file.json`;
+------+---------------+----------+
| name |     info      | response |
+------+---------------+----------+
| toto | [["LOAD",[]]] | 1        |
+------+---------------+----------+
1 row selected (0.283 seconds)

The usage of this option is not evident. So, it will be useful to mention after the error message the possibility to set it.

Error: UNSUPPORTED_OPERATION ERROR: In a list of type VARCHAR, encountered a value of type LIST. Drill does not support lists of different types. .... SET the option 'exec.enable_union_type' to true and try again;

This behaviour is used for other error, example:

...
Error: UNSUPPORTED_OPERATION ERROR: This query cannot be planned possibly due to either a cartesian join or an inequality join. 
If a cartesian or inequality join is used intentionally, set the option 'planner.enable_nljoin_for_scalar_only' to false and try again.