ORA-1254: TNS: could not resolve the connect identifier specified This error is because the connect identifier given, wrongalias, cannot be resolved into database connection details by the TNS (Transparent Network Substrate—not an acronym particularly worth remembering) layer of Oracle Net. The name resolution method to be used and its configuration is a matter for the database administrator. In this case, the error is obvious: the user entered the wrong connect identifier. The second connect attempt gives the correct identifier, orcl. This fails with ORA-12541: TNS:no listener This indicates that the connect identifier has resolved correctly into the address of a database listener, but that the listener is not actually running. Note that another possibility would be that the address resolution is faulty and is sending SQL*Plus to the wrong address. Following this error, the user should contact the database administrator and ask him or her to start the listener. Then try again. The thi...