[DRILL-7747] Function to determine Unknow fields / on fly generated missing fields

• Type: Wish
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.17.0
• Component/s: Functions - Drill
• Assignee: Unassigned
• Reporter: benj
• Created: 04/Jun/20 13:06
• Updated: 04/Jun/20 17:59

Description

it would be really useful to have a function allowing to know if a field comes from an existing column or not.

With this data:

apache drill 1.17> SELECT * FROM dfs.test.`f1.parquet`;
+---+--------+-------+
| a |   b    |   c   |
+---+--------+-------+
| 1 | test-1 | other |
| 2 | test-2 | null  |
| 3 | test-3 | old   |
+---+--------+-------+

apache drill 1.17> SELECT * FROM dfs.test.`f2.parquet`;
+----+---------+
| a  |    b    |
+----+---------+
| 10 | test-10 |
| 20 | test-20 |
| 30 | test-30 |
+----+---------+

apache drill 1.17> SELECT *, drilltypeof(c), modeof(c) FROM dfs.test.`f*.parquet`;
+------------+----+---------+-------+---------+----------+
|    dir0    | a  |    b    |   c   | EXPR$1  |  EXPR$2  |
+------------+----+---------+-------+---------+----------+
| f1.parquet | 1  | test-1  | other | VARCHAR | NULLABLE |
| f1.parquet | 2  | test-2  | null  | VARCHAR | NULLABLE |
| f1.parquet | 3  | test-3  | old   | VARCHAR | NULLABLE |
| f2.parquet | 10 | test-10 | null  | VARCHAR | NULLABLE |
| f2.parquet | 20 | test-20 | null  | VARCHAR | NULLABLE |
| f2.parquet | 30 | test-30 | null  | VARCHAR | NULLABLE |
+------------+----+---------+-------+---------+----------+

It will be nice to know when 'c' data is present because the column exists in the Parquet (or other type file) or if the value NULL was generated because the column was missing.

Example a function 'origin' that take a column name and return for each row if the value was 'generated' or 'original' (other/better keyword could be choose (exist(column)=>true/false))
Virtual Example with previous data:

apache drill> SELECT *, drilltypeof(c), modeof(c), origin(c) AS origin FROM dfs.test.`f*.parquet`;
+------------+----+---------+-------+---------+----------+-----------+
|    dir0    | a  |    b    |   c   | EXPR$1  |  EXPR$2  |  origin   |
+------------+----+---------+-------+---------+----------+-----------+
| f1.parquet | 1  | test-1  | other | VARCHAR | NULLABLE | original |
| f1.parquet | 2  | test-2  | null  | VARCHAR | NULLABLE | original |
| f1.parquet | 3  | test-3  | old   | VARCHAR | NULLABLE | original |
| f2.parquet | 10 | test-10 | null  | VARCHAR | NULLABLE | generated |
| f2.parquet | 20 | test-20 | null  | VARCHAR | NULLABLE | generated |
| f2.parquet | 30 | test-30 | null  | VARCHAR | NULLABLE | generated |
+------------+----+---------+-------+---------+----------+-----------+

Or maybe another way could be to have an implicit column name (like filename, filepath...) that contains the list of available "columns"