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PL/SQL Datatypes  «Prev  Next»
Lesson 5Adding comments
ObjectiveAdd Comments to a PL/SQL block.

Add Comments to a PL/SQL block in Oracle

Ask any IT consultant what differentiates a good programmer from a bad one, and they will answer that good programmers always comment their code. Adding comments to code promotes readability and aids in logic comprehension and code maintenance.
Comments are strictly informational and do not enforce any conditions or behavioral logic or data. In fact, the Oracle compiler ignores all comments.
Comments are used to describe the purpose and use of each code segment. PL/SQL supports two comment styles.

Single-line comments

Single-line comments begin with a double hyphen (--) anywhere on a line and can extend to the end of line.
-- This is an example of a comment

Multiline Comments

Multiline comments begin with /* and end with /. Comments can span multiple lines and multiline comments in PL/SQL can be used to comment out whole sections of code.
/* This is an example of a comment that
spans more than one line. */
This is similar to the syntax of C and Java Programming Languages.


Another great way to enhance clarity and readability of your code is to indent each subsequent level within a hanging indent level.
Below is a good example of a well-documented PL/SQL block.

/*********************************************************/
/* Name:   pet_activity.sql                              */ 
/* Description: Sample Select on Pet_Care_Log table      */ 
/* Arguments: (None)                                     */ 
/* Return Value: (None)                                  */ 
/* History:                                              */ 
/*********************************************************/
DECLARE
v_logdate DATE;
v_product NUMBER(10);
BEGIN
SELECT LOG_DATETIME,
PRODUCT_ID
INTO v_logdate,
v_product 
 FROM PET_CARE_LOG 
 WHERE PRODUCT_ID = 22;
END;

Now that you have learned about PL/SQL blocks as well as literals, identifiers, and comments, let’s use an instructional simulation to build a nested PL/SQL block.
The following simulation demonstrates the creation of a PL/SQL block that declares a variable as a number. This variable is assigned the value 42. This block includes a nested block that converts this number as a string and displays the values using
DBMS_OUTPUT.PUT_LINE.

Adding Comments
In the next lesson, we will discuss explicit versus implicit datatype conversions.