Oracle Exception ____oracle

1 ORA-00955 2 ORA-12514 ORA-12504 3 command line unable to log in

1 ORA-00955

This error occurred while building the table, the name is already used by the existing object (name is already used by a existing object), let's analyze it.
First, you must have built this form in the database;
Second, you "drop table name" hint does not have the table; third, execute look-up table statement "SELECT * from user_objects where object_name = ' Your table name '", there are three kinds of situations, one is that you write the name of the table in lowercase to find the result, When you write the name of the table, you have the result. The value of the Object_type field is displayed as a table, where you should use the drop statement, "drop table table space. Table name", where you delete the table under the specified table space, after the successful deletion of the table, two is the results of the search, The value of the Object_type field is displayed as a different type instead of a table, and you can "drop your object_type your object_name" and then build the table after it is successfully deleted, three kinds of results are always not found, At this point you can view the contents of the Synonyms folder in the Plsql tool, as shown below:

After you find it, you can perform the delete synonym statement "drop public synonym table name". When a public object has the same name as a private object (because the data is different for the user, so it can), the private object takes precedence (similar to a local variable), so here we have a public table that doesn't belong to the table space you use , you can delete a public table to build a private object (delete the private synonym statement "drop synonym tablespace. Table name"). 2 ORA-12514 ORA-12504

Plsql Connection Database error: ORA-12514 The TNS listener is currently unable to recognize the connection descriptor requesting service.
Make sure that you are using a Tnsnames.ora file, and that the instance name in the Tnsnames.ora file is correct.
Ora-12504:tns:listener was wasn't given the service_name in Connect_data.
This may be because you have installed the ORACLE database locally, you are connected to the instance name you did not fit into the%oracle_home%/network/admin/listener.ora, the configuration file is modified as follows:

Sid_list_listener =
  (sid_list = (
    Sid_desc =
      (sid_name = Clrextproc)
      (oracle_home = D:\devtool\oracle\ product\11.2.0\dbhome_1)
    #添加的实例, this instance can be configured in Tnsnames.ora
    (Sid_desc =
      (sid_name = ORCL)
      (ORACLE _home = D:\devtool\oracle\product\11.2.0\dbhome_1)))

LISTENER =
  (description_list =
    (  DESCRIPTION =
      (address = (PROTOCOL = IPC) (KEY = EXTPROC1521))
      (address = (PROTOCOL = TCP) (HOST = localhost) (PORT = 1521))
    )

Adr_base_listener = D:\devtool\oracle

3 command line cannot log in

You can log on to the database without building any users and without modifying any password, and then create the user yourself:
Sqlplus SYS/SYS@LOCALHOST/ORCL as Sysdba