Vitalii Diravka created DRILL-4614:
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Summary: Drill must appoint one data type per one column for
self-describing data while querying directories
Key: DRILL-4614
URL: https://issues.apache.org/jira/browse/DRILL-4614
Project: Apache Drill
Issue Type: Bug
Components: Execution - Data Types
Affects Versions: 1.6.0
Reporter: Vitalii Diravka
Assignee: Vitalii Diravka
Fix For: 1.7.0
While drill selects data from the directory and detects data types on-the-fly
it is possible that one field will be of several data types .
For example:
1. Create an input file as follows
20K rows with the following -
{"some":"yes","others":{"other":"true","all":"false","sometimes":"yes"}}
200 rows with the following -
{"some":"yes","others":{"other":"true","all":"false","sometimes":"yes","additional":"last
entries only"}}
2. CTAS as follows
{code:sql}
CREATE TABLE dfs.`tmp`.`tp` as select * from dfs.`data.json` t
{code}
In this case will be created parquet table as the folder with two files.
3. Select the data
{code}
select t.others.additional from dfs.`tmp`.`tp` t
{code}
The result of selecting will be mix of EXPR$0<INT(OPTIONAL)> and
EXPR$0<VARCHAR(OPTIONAL)>.
It happens because Drill defines column data type per file.
The same result with json files.
Since streaming aggregate does not support schema changes this issue makes
impossible of using aggregate functions with query results.
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