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  1. Core Server
  2. SERVER-34741

Move $match in front of $group if condition is on group key

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Details

    • Fully Compatible
    • v4.2
    • Query 2019-06-03, Query 2019-06-17, Query 2019-07-01

    Description

      In case of views created on results of a $group, if the subsequent query is filtering on _id field then it should be possible to push that $match in front of $group transforming it into filter against whatever field is being grouped.

      Example:

      Vew definition:

      [ {$group:{_id:"$city", ...}} ] 
      

      Query on view:

      {$match: {_id:{$in:["NY", "SF"]}}}
      

      Pipeline transformation:

      // from
      [ {$group:{_id:"$city", ...}}, {$match: {_id:{$in:["NY", "SF"]}}} ] 
      // to
      [{$match: {city:{$in:["NY", "SF"]}}}, {$group:{_id:"$city", ...}} ] 
      

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            backlog-query-optimization Backlog - Query Optimization
            asya.kamsky@mongodb.com Asya Kamsky
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              Created:
              Updated:
              Resolved: