[GitHub] [incubator-druid] Dylan1312 opened a new issue #8970: Expressions within aggregations can no longer use virtual columns

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

Dylan1312 opened a new issue #8970: Expressions within aggregations can no longer use virtual columns
URL: https://github.com/apache/incubator-druid/issues/8970
 
 
   ### Affected Version
   
   0.15.0-incubating
   0.15.1-incubating
   0.16.0-incubating
   
   ### Description
   
   Prior to 0.15.0, an expression within an aggregation could use a virtual column. In later versions it seems that a virtual column used within an expression will always evaluate to 0.
   
   This was useful as it allowed expressions using _time to be evaluated once per segment (within a virtual column) rather than evaluating it every aggregation operation.
   
   I'm still trying to decipher why but it looks like when the virtual column selector is loaded, the returned value is a "ArrayExprEval" which has a hardcoded value of 0 for asLong.
   
   bit of a contrived example but to show what's changed
   
   `{
     "dataSource" : "test",
     "intervals" : [
       "2019-11-01/2019-11-02"
     ],
     "granularity" : "all",
     "aggregations" : [
       {
         "type" : "longSum",
         "name" : "computed_value",
         "expression" : "1 + two"
       }
     ],
     "virtualColumns" : [
       {
         "name" : "two",
         "expression" : "2",
         "type" : "expression"
       }
     ],
     "queryType" : "timeseries"
   }`
   
   returns 
   
   `[
       {
           "timestamp": "2019-11-01T00:00:00.000Z",
           "result": {
               "computed_value": 1574832721
           }
       }
   ]`
   
   on 0.14.2
   
   but 
   
   `
   [
       {
           "timestamp": "2019-11-01T00:00:00.000Z",
           "result": {
               "computed_value": 0
           }
       }
   ]
   `
   on 0.16.0
   
   
   

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