Question

My table is something like this:

_id     time    name    isNotFirstEntry
1       55555   aaa     0
2       66666           1
3       77777           1
4       88888   bbb     0
5       99998           4
6       99999           4

i.e. for duplicate entries, name is null and the _id of the original entry is stored in isNotFirstEntry.

I want do retrieve _id, time, name, no. of duplicate entries as n where name!=null

I tried something like this:
select _id, time, name, (select count(isNotFirstEntry) from mytable where isNotFirstEntry=_id) as n from mytable where name!=null

but of course that doesnt work. The _id in the nested query is not the same as that of the outside part. I need to access _id of the outside part from the nested query.

Im using android sdk, so i can use sqlite only.

Answer 1

You need to do a join. You can do this as a correlated subquery:

select mt._id, mt.time, mt.name,
       (select count(mt2.isNotFirstEntry)
        from mytable mt2
        where mt2.isNotFirstEntry=mt._id
       ) as n
from mytable mt
where mt.name!=null

Or as an explicit join with group by:

select mt._id, mt.time, mt.name, count(mt2._id) as n
from mytable mt left outer join
     mytable mt2
     on mt._id = mt2.isNotFirstEntry
where mt.name is not null
group by mt._id, mt.time, mt.name