[GitHub] [incubator-druid] jon-wei commented on issue #7584: Cant refer to variables declared inside sql statements for post aggregations

[GitBox <gi...@apache.org>]

jon-wei commented on issue #7584: Cant refer to variables declared inside sql statements for post aggregations
URL: https://github.com/apache/incubator-druid/issues/7584#issuecomment-489768496
 
 
   This example:
   ```
   select count(*), dataSource AS s
   from druid_rules
   group by s;
   ```
   
   is not the same type of query as
   ```
   SELECT "cluster", sum ("mem_limit") as memTotal, sum ("mem_used") as memUsed,  
   (memUsed*100.0/memTotal)  as pct  /*this causes problems*/
   FROM "metrics"
   WHERE   "__time" >= TIMESTAMP '2019-04-30 20:17:46' AND "__time" < TIMESTAMP '2019-04-30 20:17:48'   
   group by "cluster"
   ```
   See the following:
   
   ```
   mysql> select count(*), SUM(partitioned) as psum, (psum*100.0) as psumhundred, dataSource AS s from druid_segments group by s;
   ERROR 1054 (42S22): Unknown column 'psum' in 'field list'
   ```
   
   ```
   mysql> select count(*), SUM(partitioned) as psum, (SUM(partitioned)*100.0) as psumhundred, dataSource AS s from druid_segments group by s;
   +----------+------+-------------+------------+
   | count(*) | psum | psumhundred | s          |
   +----------+------+-------------+------------+
   |        1 |    1 |       100.0 | wikipedia  |
   |       44 |   44 |      4400.0 | wikipedia2 |
   +----------+------+-------------+------------+
   2 rows in set (0.00 sec)
   ```

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