Can't compute sql sub-queries

[jerome73]

Hello,

I would like to compute percent metrics using the _sql api.
To do so I run this type of query:

POST _opendistro/_sql
{
  "query" : "SELECT count(*)/(SELECT count(*) FROM ml_algos), algo_version FROM ml_algos GROUP BY algo_version"
}```

But this returns the following error:

```json
{
  "error": {
    "reason": "There was internal problem at backend",
    "details": "unsupported expr: com.alibaba.druid.sql.ast.statement.SQLSelect@1d60737e",
    "type": "RuntimeException"
  },
  "status": 503
}

FYI this type of query runs well against db like sqlite.
Is this supported by opendistro sql plugin ?

[dai-chen]

Hi @jerome73 , thanks for reporting the issue! Unfortunately, this is not supported yet. For now only subqueries in FROM and WHERE can be supported. Please check out our doc: https://github.com/opendistro-for-elasticsearch/sql/blob/develop/docs/user/dql/complex.rst#subquery