You don't need SqlDataAdapter and DataTable to get a value, you can use the more lightweight SqlDataReader
, see example here: Retrieving Data Using a DataReader | Microsoft Docs
string value5 = reader.GetString(0));
Also use parameterized queries, especially in security sensitive queries like this one !
See: c# - How to use sql parameters for a select query? - Stack Overflow
If a value is found in tbladmin
, it means that an admin was found, other users can be found in tbluser