Don't. If you have a recordId, assume it exists and delete it - catch the exception if it did not. Adding checks like the one you proposed might say it exist, and still be deleted (by someone else) an instance later (unless it's an atomic operation, which I doubt).
if you delete it while it doesn't exist SQL will return something like: "0 rows deleted".
Deletefrom tableX where myconstraint='Myconstraint';
--> query returned in 10 ms: 0 rows deleted
If you do it in code you can get that by reading out the NrOfRowsAffected property when doing an ExecuteNonQuery statement. Same goes for Insert and Update queries eg.
as someone already replied, checking if it exists is inaccurate at best and doesn't add any functional advantage.
if you really, really must check it. Perform a select query perhaps with a count.
Select count(id) from tableX where myconstraint='Myconstraint'