Synonyms

A synonym is an alias for a database object (such as a table, view, materialized view, sequence, stored procedure, function, package, type, or user-defined type). You can also create a synonym for another synonym. A synonym is just an alias and does not occupy any space. It is defined only in the data dictionary. This topic describes the types, characteristics, and privileges of synonyms.

Synonym types

There are two types of synonyms: public synonyms and private synonyms.

A public synonym belongs to the PUBLIC group and can be accessed by all users. A private synonym belongs to the owner of the object and can be accessed by other users only after they are explicitly authorized.

Public synonyms are generally created by DBA. If you want to create a public synonym, you need the CREATE PUBLIC SYNONYM system privilege.

Basic characteristics

Synonyms extend the scope of database usage and enable seamless interaction between different database users. They are often used to simplify object access and enhance the security of object access.

Create a synonym

You can execute the CREATE SYNONYM statement to create a synonym. The syntax is as follows:

CREATE [ OR REPLACE ] [ PUBLIC ]
SYNONYM [ schema. ]synonym
FOR [ schema. ]object;

Parameter description

After a synonym is created, you can query the USER_SYNONYMS, ALL_SYNONYMS, or DBA_SYNONYMS view to view the synonym.

Examples

• Create a private synonym.

  obclient> CREATE TABLE t1(c1 INT);
  obclient> CREATE SYNONYM s1 FOR t1;
  obclient> INSERT INTO s1 VALUES(1);
  obclient> SELECT * FROM s1;
  +------+
  | c1   |
  +------+
  |    1 |
  +------+
  1 row in set
  

• Create a public synonym.

  obclient> CREATE PUBLIC SYNONYM syn_pub FOR t1;
  obclient> SELECT * FROM syn_pub;
  +------+
  | c1   |
  +------+
  |    1 |
  +------+
  1 row in set
  

Drop a synonym

You can execute the DROP SYNONYM statement to drop a synonym. The syntax is as follows:

DROP [PUBLIC] SYNONYM [ schema. ]synonym;

Parameter description

Examples

• Drop a private synonym.

  obclient> DROP SYNONYM test.s1;
  Query OK, 0 rows affected
  

• Drop a public synonym.

  obclient> DROP PUBLIC SYNONYM syn_pub;
  Query OK, 0 rows affected
  

Considerations

To create a synonym, you must meet the following privilege requirements:

• To create a private synonym in the current user's schema, you must have the CREATE SYNONYM privilege.

• To create a private synonym in a schema other than the current user's schema, you must have the CREATE ANY SYNONYM privilege.

• To create a public synonym, you must have the CREATE PUBLIC SYNONYM privilege.

• You do not need the privilege to access the object for which the synonym is created.

/* Connect to the `SYS` user */
obclient> CREATE USER syn_user IDENTIFIED BY syn_user;
obclient> GRANT CREATE ON syn_user.* TO syn_user;
obclient> GRANT SELECT ON syn_user.* TO syn_user;

/* Connect to the `syn_user` user and create a synonym. The operation fails. */
obclient> CREATE SYNONYM syn_1 FOR t1;
ERROR-00600: internal error code, arguments: -5036, Access denied; you need (at least one of) the CREATE SYNONYM privilege(s) for this operation

/* Connect to the `SYS` user and grant the CREATE SYNONYM privilege to the `syn_user` user. */
obclient> GRANT CREATE SYNONYM ON *.* TO syn_user;

/* Connect to the `syn_user` user again. */
obclient> CREATE SYNONYM syn_1 FOR t1;