Declare @Table Table
(
ColDateTime Varchar(100)
)
Insert into @Table
Select '2042-04' UNION ALL
Select '2011-01'
Select ColDateTime As VarcharCol,
Cast(
substring(ColDateTime,0,charindex('-',ColDateTime))+substring(ColDateTime,charindex('-',ColDateTime)+1,len(ColDateTime))+'01'
As DateTime) As DateTimeCol
from @Table