Sybase Stored Procedure Problems

Q: SYBASEStored ProcedureWhy is this sentence not executed?
Select @ nSerialNo = serialno from schedule where phonenum = @ strPhoneNum and type = @ nType
If @ rowcount = 0
Begin
...
End
Else
Begin
...
End
The aboveSelectThe result is an empty record set. When a stored procedure is executed to an empty record set, it will return?
A:If exists (select @ nSerialNo = serialno from schedule where phonenum = @ strPhoneNum and type = @ nType)ThisStatementIs there a problem with the logic?
If existsIs it generally used to determine whether a similar record exists? Do you want to assign values to existing results now? In fact, it is better to writeIf existsSelect 1 from schedule where phonenum = @ strPhoneNum and type = @ nType)
Check whether such a record exists and perform corresponding processing.