What Symbols are Used in Oracle Database

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Several symbols that are used in Oracle might represent different meanings in different place.

Question mark ?

ORACLE HOME

? (a Question Mark) in a path string represents the environmental variable of ORACLE_HOME. It's usually $ORACLE_HOME in UNIX or Linux, %ORACLE_HOME% in Windows.

SQL> alter tablespace temp add datafile '?/dbs/temp02.dbf' size 200M;

You may also use the environment variable $ORACLE_HOME directly in the statement.

SQL> alter tablespace temp add datafile '$ORACLE_HOME/dbs/temp02.dbf' size 200M;

Please do NOT use ? or $ORACLE_HOME in ALTER SYSETM statements, they won't be interpreted.

At sign @

Execute start with

If the @ sign is used at the beginning of a path string, then it notifies Oracle utility to execute the script followed with.

SQL> @?/rdbms/admin/awrrpt.sql

ORACLE_SID

If the @ sign is in a path string, then it represents the environmental variable of ORACLE_SID. It's usually $ORACLE_SID in UNIX or Linux, %ORACLE_SID% in Windows.

Example 1:

SQL> alter tablespace tablespace_name add datafile tempfile@.dbf;

Example 2:

SQL> create pfile='?/dbs/init@.ora' from spfile;

You may also use the environment variable $ORACLE_SID in the statement.

SQL> create pfile='?/dbs/init$ORACLE_SID.ora' from spfile;

Followed by a Connection String (or a TNS Name)

If the @ is in a connection string, it means the following identifier is a hostname, let's see some examples. The first one is the local naming method.

[oracle@test ~]$ sqlplus sys/password@ora12c as sysdba

The second is the easy connect method.

[oracle@test ~]$ sqlplus sys/password@ora12c-server:1521/ora12c as sysdba

For your reference, the following documents contain more about those symbols:

  1. Starting SQL*Plus
  2. Administering Oracle Database
  3. Connecting to a Database

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