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Soubhagya Ranjan 2Soubhagya Ranjan 2 

getting error through trigger

while i am inserting record i am getting these error 

Apex trigger DuplicateCoreCustomer caused an unexpected exception, contact your administrator: DuplicateCoreCustomer: execution of BeforeInsert caused by: System.QueryException: Non-selective query against large object type (more than 200000 rows). Consider an indexed filter or contact about custom indexing. Even if a field is indexed a filter might still not be selective when: 1. The filter value includes null (for instance binding with a list that contains null) 2. Data skew exists whereby the number of matching rows is very large (for instance, filtering for a particular foreign key value that occurs many times): Trigger.DuplicateCoreCustomer: line 12, column 1

why i am getting theses errors and how to avoid these 
Hi Soubhagya,

I hope solution for your question is there in the below link.Refer this...

Thanks & Best Regards,