根据加入SQL Server的条件执行查询

I want to fetch data from the table [DL_TRN]. If the record is not present in that table then I want to fetch details from another table [D_Loan], Same condition for [FL_TRN] table and [F_LOAN].I mentioned only two loan tables(Demand Loan and Festival Loan) but I have to do work with multiple types loan tables in the same query.I triedI want to fetch data from the table [DL_TRN]. I