Используйте как показано ниже -
Select Distinct
a.CID,
CONCAT (RTRIM(Name1), ' ', RTRIM(Name2)) As [Name of Policy Holder],
DOC = cast(InsuStartDate as date)
ИЛИ
Select Distinct
a.CID,
CONCAT (RTRIM(Name1), ' ', RTRIM(Name2)) As [Name of Policy Holder],
cast(InsuStartDate as date) DOC