How to handle exception in WCF

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C#6.0

I have a wcf service. in my service i am validating the data and saving the data in db. when my client send the wrong data i am returning some mandatory fields are empty. but whenever my client send a correct data to me that time am saving the data in db and am returning the success message but if my db throw an exception but here i don't want to return to the client with failure message, here i want to recall the db and save the data how can i handle this requirement in my service but i want to release the call at exception with success message

What I have tried:

as off now i haven't tried anything