DBMS_OUTPUT.PUT_LINE is a procedure in Oracle’s PL/SQL that allows developers to display output from PL/SQL blocks, procedures, functions, packages, and triggers. It’s part of the DBMS_OUTPUT package, which provides a way for PL/SQL programs to communicate with the outside world in a simple manner. This is especially useful during development and debugging phases, where developers need to inspect values of variables, parameters, or to trace the execution flow of the PL/SQL code.
Basic Syntax
The basic syntax of DBMS_OUTPUT.PUT_LINE is as follows:
DBMS_OUTPUT.PUT_LINE(message);
message: The string or variable content you wish to display. This can be a text literal, a variable, or an expression that results in a string.
Key Points
Buffer Limit: The DBMS_OUTPUT package works by accumulating the messages in a buffer until the buffer is displayed to the screen. By default, the buffer size is limited, but it can be increased up to a limit using the DBMS_OUTPUT.ENABLE(buffer_size) procedure. If the buffer size is not explicitly enabled, it might result in some messages not being displayed if the buffer overflows.
Displaying Output: To see the output of DBMS_OUTPUT.PUT_LINE, you need to make sure that the client tool you are using is set up to display the DBMS_OUTPUT buffer. In SQL*Plus and SQL Developer, this is typically done by running the command SET SERVEROUTPUT ON. This command needs to be executed before running your PL/SQL block.
Usage: It is commonly used for debugging purposes, to print log messages, or to display results of PL/SQL blocks during development. However, it’s not recommended for use in production code as a means of user interaction or logging due to its limitations and the dependence on client tool configurations.
Example
BEGIN
DBMS_OUTPUT.PUT_LINE('Hello, World!');
END;
This simple PL/SQL block will output Hello, World! to the screen, assuming that the server output is enabled in your SQL client tool.
Considerations
Performance: Excessive use of DBMS_OUTPUT.PUT_LINE can impact performance, especially with large volumes of data or in loops, due to the overhead of managing the output buffer.
Alternative for Logging: For production environments or more complex logging needs, consider using logging frameworks or writing directly to log files or tables designed for logging purposes.
DBMS_OUTPUT.PUT_LINE is a basic but powerful tool in the PL/SQL developer’s toolkit for interactive debugging and simple messaging. However, its usage should be appropriately managed, especially in the context of production code.