Oracle SQL is a powerful tool for managing and manipulating data in relational databases. One of the most common tasks performed by database administrators and developers is creating tables to store data. In addition to defining the structure and properties of these tables, it may also be necessary to add comments explaining the purpose and usage of the table. In this tutorial, we will explore the process of creating a table comment in Oracle SQL.
Creating Tables and Adding Comments in Oracle SQL
Creating a table in Oracle SQL involves defining the table’s name, the names and types of its columns, and any constraints or properties related to those columns. A comment is a textual note attached to a database object, such as a table or column. The comment can provide additional context or explanation about the function of the object.
CREATE TABLE my_table (
id NUMBER PRIMARY KEY,
COMMENT ON TABLE my_table IS ‘This table stores user details.’;
The above code snippet demonstrates how to create a table named ‘my_table’ with three columns: ‘id’, ‘name’, and ‘age’. Following the table creation statement is a COMMENT ON TABLE statement which adds the comment ‘This table stores user details.’ to the table.
Understanding the COMMENT ON TABLE Statement
The COMMENT ON TABLE statement is used to add a comment to an existing table in Oracle SQL. The statement takes the general form below:
COMMENT ON TABLE table_name IS ‘comment’;
In this statement, table_name is the name of the table to which the comment is being added, and ‘comment’ is the string of text that constitutes the comment.
When the COMMENT ON TABLE statement is executed, the comment is stored in the table’s metadata. This means that it does not affect the function of the table or the data stored in the table, but it can be retrieved and viewed by users who have permission to see the table’s metadata.
Retrieving Table Comments
Comments added to tables in Oracle SQL can be retrieved by querying the USER_TAB_COMMENTS view. This view contains a row for each table owned by the current user, along with any comments associated with those tables.
SELECT table_name, comments FROM user_tab_comments WHERE table_name = ‘MY_TABLE’;
This query retrieves the comment for the ‘my_table’ table. The results would look something like this:
| TABLE_NAME | COMMENTS |
| MY_TABLE | This table stores user details.|
As you can see, creating comments on tables in Oracle SQL can improve database maintainability by providing descriptive context about the database’s objects. It’s an innovative way to self-document the database and enhance understanding for future reference.