Aggregation pipeline for one use case

MongoDB for Academia MongoDB for Students
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I have 3 collection . coll1, coll2, coll3 . Each collection have multiple fields which includes state and priority . state field value can be “OPEN” . “INREVIEW”, "CLOSED"and priority value can be “HIGH”, “MEDIUM”, “LOW”. Now i would like to get the total count ,“OPEN” count, “INREVIEW” COUNT also “HIGH” , “MEDIUM”, “LOW” count for each collection. One tricky part here is I would like to execute single pipeline to get these result. Can some one help on this ?

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Take a look at