How to query all libraries in oracle

With the popularization and deepening of enterprise information construction, the application scope of databases has become more and more extensive, and querying data in databases has become one of the essential operations for enterprise information operation management. In the Oracle database, we need to master how to query related operations of all libraries. This article will introduce the methods of Oracle querying all libraries from the following aspects.

1. Use data dictionary to query all libraries

data dictionary is a built-in table in Oracle database, which stores various data dictionary information, including all database objects. By querying the data dictionary, we can obtain relevant information about all databases. In the Oracle database, all data dictionary tables start with 'DBA_', 'ALL_' or 'USER_'. 'DBA_' is to view all data dictionary tables, and 'ALL_' is to view the data that the current user has permission to view. Dictionary table, 'USER_' is to view object information owned by the current user.

We can query the data dictionary through the following SQL statement to obtain all database information:

SELECT DISTINCT owner FROM dba_objects;

After executing this statement, Oracle will return a list containing all owners in the database . The owner is the user who created the object in the database. There can be multiple owners in a database. We can use this statement in the query to obtain information from all databases. The database information obtained by this method includes database name, owner name, object type and other related information.

2. Use Enterprise Manager to query all libraries

Oracle provides a management tool called Enterprise Manager, which can help us manage database instances. In Enterprise Manager, we can query various information about the database instance, including all library-related information.

The specific steps are as follows:

1. First log in to Enterprise Manager and select a database instance.

2. Click ‘Control’ on the left menu bar, and then select ‘Library’. You can see all existing databases in ‘Library’.

3. Click the database name to be queried in ‘Library’, and Enterprise Manager will display the detailed information of the database instance.

This method can show us a complete library list, including database name, status, size and other related information.

3. Use sqlplus to connect to all libraries

sqlplus is a command line tool that allows us to connect to an Oracle database instance through the command line and query database information. We can use sqlplus to connect to all database instances, and then use SQL statements to query database related information. The specific steps are as follows:

1. Open the command line window and enter the following command to connect to the Oracle database instance:

sqlplus system/password@TNSNAME

Where, 'system' is the user name connected to the database, 'password' is the user's password and 'TNSNAME' is the connection string to the database. If you need to connect to multiple databases, you can replace TNSNAME with the corresponding connection string.

2. After the connection is successful, query the database related information by running SQL statements. For example:

SELECT name FROM v$database;

This command will return the name of the current database instance. We can execute similar commands in the command line to get more information about the database instance.

The advantage of this method is that you can connect to all database instances at once and then execute SQL statements to query related information. The disadvantage is that you need to enter multiple usernames and passwords to connect.

4. Use PL/SQL to query all libraries

Oracle PL/SQL is a procedural programming language that allows us to access database information programmatically. We can write a simple PL/SQL program to query the information of all libraries in the database. The specific steps are as follows:

DECLARE
DB_NAME VARCHAR2(255);
BEGIN
    FOR i IN (SELECT name FROM v$database)
    LOOP
        DB_NAME := i.name;
        dbms_output.put_line(DB_NAME);
    END LOOP;
END;
/

This code uses PL/SQL to loop through each database instance in the v$database view and output the database instance name to the console.

Conclusion

This article introduced four methods for Oracle to query all libraries, including using data dictionary, Enterprise Manager, sqlplus and PL/SQL. Each method has its own advantages and disadvantages, and we can choose to use the corresponding method according to the specific situation. No matter which method we choose, we need to have certain Oracle database operation foundation and skills to better manage database instances.

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