Question

Please help me find the MongoDb equivalent for the SQL:

select val from tblName where colName1 = 7 
group by colName2 
order by colName3 desc, colName4 desc

Answer 1

For everything except the grouping :

db.tblName.find({colName1:7},{val:1}).sort({colName3:-1, colName4:-1})

But for grouping, you are either looking at MapReduce or the new Aggregation Framework (the Aggregation Framework isn’t in a stable build yet, it is only in 2.1.0 and odd-numbered releases aren’t production ready)

With the Aggregation Framework, based upon a quick scan of the documentation and no access to the latest Mongo (ie copy & pasting won’t work – it’s a basis on which to start):

db.tblName.aggregate(
    {$match : {colName1:7}}, //filter by colName1=7
    {$project: {val:1,colName2:1,colName3:1,colname4:1}}, //keep only the specified fields
    {$group: {colname2:1}}, //group by colName2 - this is the bit I'm least clear on
    {$sort: {colName3:-1; colname4:-1}}, //sort
    {$project: {val:1}} //keep only the val column
)

If anyone wants to improve on the syntax (ie someone with access to a Mongo with Aggregation) feel free 🙂