I want to get records for which the child records are not null. I tried to use the resolution provided at the link mentioned below but it did not help. I tried the query with "!= null" as well as "!=''".

 https://developer.salesforce.com/forums/?id=906F00000008lxBIAQ .

I have been breaking my head over it ... hope someone else can help with this.

The query -

Select
(Select Id, FieldA, FieldB, FieldC From Child__r where FieldA IN
('Value1', 'Value2','Value3')  ) ,

o.Parent_Date_Time__c From Parent__c o

where o.Id IN (Select Parent__c from Child__c where Parent__c != '') AND

o.LastModifiedDate >= 2013-05-01T23:59:59Z AND
o.Parent_Date_Time__c = LAST_N_DAYS: 15