>Hi,
>
>My application creates one SQL Server connection at the top of the application and then relies on it for all calls to SQL Server. But I understand that the connection can time out. Therefore, do you recommend that the program checks if the connection is still valid (by e.g. by SELECT CAST(1 as BIT) or some other way) every time the program needs to connect (to SQL Select or Update)? TIA.

There's no point. If the connection is *down* then it doesn't matter whether the SQL is simple or complex - it will fail immediately.
And if it is *up* there is no quarantee that it will not go down whilst the query is executing anyway.....

Of course, if, as suggested, you switch to closing and re-opening connections it's not relevant anyway.

>UPDATE. An idea just occurred to me. What if on every call to the SQL Server I store the time of the call to the application property. Then, every time another call needs to be made, the code would check how much time elapsed since the last call. Then if the time is greater than the set Time Out, create new connection, otherwise, use existing.
>Does it make sense? Is it practical?