Question

Pretty simple question that I can’t quite find the answer for:

Is there a simple and safe† way to cast a varchar to datetime in SQL Server?

† i.e. gracefully handle non-datetime strings with a default datetime value

Answer 1

You can filter your rows using the isdate function. This query returns three rows without any conversion errors:

with v as (
    select '20110714' value union all
    select '2011-07-15' union all
    select '3/22/2011' union all
    select 'foo' 
)
select cast(value as datetime)
from v
where isdate(value) = 1

Edit

When you want a default vaue (like the current date/time), you could do something like this:

select case when isdate(value) = 1 then cast(value as datetime) else getdate() end