How to query a user's tablespace through Oracle SQL

Table space is the basic unit for Oracle database to manage data. In Oracle database, both user data and system data are stored in table spaces. When we create a user, we need to allocate a tablespace for this user. Therefore, when managing an Oracle database, it is often necessary to query the user's table space and the usage of the table space. This article will introduce how to query the user's table space through Oracle SQL.

In Oracle database management, table space is a method of dividing the database into several logical areas. Each tablespace consists of a set of data files that are physically stored on disk. Each table space contains some related database objects, such as tables, indexes, and stored procedures. When creating a table space, we need to specify the name of the table space, data files, storage parameters and other information. Normally, we allocate a table space for each user.

In Oracle database, the system table space is the table space used to store system objects, such as data dictionary, stored procedures and internal tables. If we need to query the table space of a certain user, we can do it through the following steps:

Step 1: Log in to the Oracle database

We first need to log in to the Oracle database management system, you can use SQLPlus tool or Oracle SQL Developer tool, etc. Taking the SQLPlus tool as an example, we enter the following command to log in:

$ sqlplus / as sysdba

This command will log in to the Oracle database as a system administrator.

Step 2: Query the user table space

We can use the following SQL query statement to query the table space of a certain user:

SELECT USERNAME, DEFAULT_TABLESPACE
FROM DBA_USERS
WHERE USERNAME='username';

Among them, USERNAME represents the user to be queried. name, DEFAULT_TABLESPACE represents the user's default table space.

Step 3: Query the table space usage

If we need to know the table space usage of a certain user, we can use the following SQL query statement:

SELECT
A.TABLESPACE_NAME,
A.BYTES / (1024 * 1024) AS "TOTAL_MB",
(B.BYTES - NVL(F.BYTES, 0)) / (1024 * 1024) AS "USED_MB", 
NVL(F.BYTES, 0) / (1024 * 1024) AS "FREE_MB", 
(B.BYTES - NVL(F.BYTES, 0)) / A.BYTES * 100 AS "USED_PERCENTAGE",
NVL(F.BYTES, 0) / A.BYTES * 100 AS "FREE_PERCENTAGE"
FROM
(SELECT TABLESPACE_NAME, SUM(BYTES) BYTES FROM DBA_DATA_FILES GROUP BY TABLESPACE_NAME) A, 
(SELECT TABLESPACE_NAME, SUM(BYTES) BYTES FROM DBA_SEGMENTS GROUP BY TABLESPACE_NAME) B,
(SELECT TABLESPACE_NAME, SUM(BYTES) BYTES FROM DBA_FREE_SPACE GROUP BY TABLESPACE_NAME) F 
WHERE A.TABLESPACE_NAME = B.TABLESPACE_NAME(+) AND A.TABLESPACE_NAME = F.TABLESPACE_NAME(+);

This The SQL query statement will return the total size (TOTAL_MB), used space (USED_MB), free space (FREE_MB), used space percentage (USED_PERCENTAGE) and free space percentage (FREE_PERCENTAGE) of each table space.

Step 4: Summary

In Oracle database management, table space is a very important concept. We need to allocate a table space for each user, and often need to query the user's table space and table space usage. By using the above SQL query statement, we can easily query the table space in the Oracle database and understand the usage of the table space.

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