How can I view the data volume of each table in Oracle?

You can use the following SQL query to view the amount of data in each table:

SELECT table_name, num_rows
FROM all_tables
WHERE owner = 'your_schema_name';

Replace your_schema_name with the name of the schema or user you want to query. This will return the names and data sizes of each table under the specified schema or user. Please note that this query can only provide estimated data sizes as it is based on statistics rather than actual counts.