Retrieving distinct documents from Solr - solr

Question

I've had hard time explaining and finding what I need so please put your self in my shoes for a moment.
My requirement comes from a relational database background. I may be using Solr to do something it wasn't designed to do, or may be it can do what I need, I still need to confirm that. Hopefully you can assist me.
After indexing numerous documents into Solr. I need to retrieve distinct documents based on a filter. Just think about it as retrieving distinct rows while also applying a WHERE condition.
For example, in a relational database, I may have the following columns
(Country) (City) (Whatever)
Egypt Cairo Hospitals
Egypt Alex Schools
Egypt Mansoura Hospitals
Egypt Cairo Schools
If I perform this query: SELECT DISTINCT Country, City FROM mytable
I should get the following rows
(Country) (City)
Egypt Alex
Egypt Mansoura
Egypt Cairo
Now after indexing the original table (SELECT * FROM mytable), how can I achieve the SAME output from Solr ? How can I retrieve documents by saying that I need these documents to be distinct based on some fields ? I will also need to apply a not null filter for a specific field.
I don't need statistics of any kind, I only need to get the documents.
I hope I was clear enough. Thank you for your time.

Answer 1

this would be achievable with field collapsing by grouping by multiple fields, but unfortunately only one field is supported right now. There is an open issue, check it out.

Answer 2

Did you try with facet?
You should do somethings like this:
http://localhost:8983/solr/select/?q=*:*&facet=on&facet.field=city&facet.field=country
he will return you all the city (with a distinct) and the his count.
Here there is the wiki if you want to learn more about it.
I hope this help you.

Answer 3

Another good solution available from Solr 4 is based on Pivot (Decision Tree) Faceting.
Try with:
/solr/collection1/select?q=*:*&facet=true&facet.pivot=Country,City
This should return:
"facet_counts" : {
"facet_queries" : {},
"facet_fields" : {},
"facet_dates" : {},
"facet_ranges" : {},
"facet_pivot" : {
"Country,City" : [ {
"field" : "Country",
"value" : "Egypt",
"count" : 4,
"pivot" : [ {
"field" : "City",
"value" : "Cairo",
"count" : 2
}, {
"field" : "City",
"value" : "Alex",
"count" : 1
}, {
"field" : "City",
"value" : "Mansoura",
"count" : 1
} ]
} ]
}
}