ALTER DATABASE

Description

Alters a database, including its name, owner, object isolation, and connection limitation.

Precautions

Only the database owner or a user granted with the ALTER permission can run the ALTER DATABASE command. System administrators have this permission by default. The following are permission restrictions depending on attributes to be modified:
- To change the database name, you must have the CREATEDB permission.
- To change a database owner, you must be a database owner or system administrator and a member of the new owner role, with the CREATEDB permission.
- To change the default tablespace of the database, the user must have the CREATE permission for creating tablespaces. This statement physically migrates tables and indexes in a default tablespace to a new tablespace. Note that tables and indexes outside the default tablespace are not affected.
You are not allowed to rename a database in use. To rename it, connect to another database.

Syntax

Modify the maximum number of connections to the database.

ALTER DATABASE database_name 
    [ WITH ] CONNECTION LIMIT connlimit;

Rename the database.

ALTER DATABASE database_name 
    RENAME TO new_name;

Change the database owner.

ALTER DATABASE database_name 
    OWNER TO new_owner;

Change the default tablespace of the database.
```
ALTER DATABASE database_name 
    SET TABLESPACE new_tablespace;
```
If some tables or objects in the database have been created in new_tablespace, the default tablespace of the database cannot be changed to new_tablespace. An error will be reported during the execution.

Modify the session parameter value of the database.

ALTER DATABASE database_name 
    SET configuration_parameter { { TO | = } { value | DEFAULT } | FROM CURRENT };

Reset the database configuration parameter.

ALTER DATABASE database_name RESET 
    { configuration_parameter | ALL };

Modify the object isolation attribute of the database.
```
ALTER DATABASE database_name [ WITH ] { ENABLE | DISABLE } PRIVATE OBJECT;
```
- To modify the object isolation attribute of a database, the database must be connected. Otherwise, the modification will fail.
- For a new database, the object isolation attribute is disabled by default. After this attribute is enabled, common users can view only the objects (such as tables, functions, views, and columns) that they have the permission to access. This attribute does not take effect for administrators. After this attribute is enabled, administrators can still view all database objects.

Parameters

database_name
Specifies the name of the database whose attributes are to be modified.

Value range: a string that complies with the Identifier Naming Conventions.
connlimit
Specifies the maximum number of concurrent connections that can be made to this database (excluding administrators' connections).

Value range: an integer ranging from –1 to 2³¹ – 1. You are advised to set this parameter to an integer ranging from 1 to 50. The default value –1 indicates that there is no restriction on the number of concurrent connections.
new_name
Specifies the new name of a database.

Value range: a string that complies with the Identifier Naming Conventions.
new_owner
Specifies the new owner of a database.

Value range: a string. It must be a valid username.
new_tablespace
Specifies the new default tablespace of a database. The tablespace exists in the database. The default tablespace is pg_default.

Value range: a string. It must be a valid tablespace name.
configuration_parameter
- value
  Sets a specified database session parameter to a specified value. If the value is DEFAULT or RESET, the default setting is used in the new session. OFF disables the setting.
  
  Value range: a string.
  - DEFAULT
  - OFF
  - RESET
- FROM CURRENT
  Uses the value of configuration_parameter of the current session.
FROM CURRENT
Sets the value of the database based on the current connected session.
RESET configuration_parameter
Resets the specified database session parameter.
RESET ALL
Resets all database session parameters.

Modify the default tablespace of a database by moving the table or index in the old tablespace into the new tablespace. This operation does not affect the tables or indexes in other non-default tablespaces.
The modified database session parameter values will take effect in the next session.