Procedures and Functions are the subprograms which can be created and saved in the database as database objects. They can be called or referred inside the other blocks also. Apart from this, we will cover the major differences between these two subprograms. Also, we are going to discuss the Oracle built-in functions. In this Oracle Stored Procedure tutorial, you will learn-

Terminologies in PL/SQL Subprograms What is Procedure in PL/SQL? What is Function? Similarities between Procedure and Function Procedure Vs. Function: Key Differences Built-in Functions in PL/SQL

Terminologies in PL/SQL Subprograms

Before we learn about PL/SQL subprograms, we will discuss the various terminologies that are the part of these subprograms. Below are the terminologies that we are going to discuss.

Parameter:

The parameter is variable or placeholder of any valid PL/SQL datatype through which the PL/SQL subprogram exchange the values with the main code. This parameter allows to give input to the subprograms and to extract from these subprograms.

These parameters should be defined along with the subprograms at the time of creation. These parameters are included in the calling statement of these subprograms to interact the values with the subprograms. The datatype of the parameter in the subprogram and the calling statement should be same. The size of the datatype should not mention at the time of parameter declaration, as the size is dynamic for this type.

Based on their purpose parameters are classified as

IN Parameter OUT Parameter IN OUT Parameter

IN Parameter:

This parameter is used for giving input to the subprograms. It is a read-only variable inside the subprograms. Their values cannot be changed inside the subprogram. In the calling statement, these parameters can be a variable or a literal value or an expression, for example, it could be the arithmetic expression like ‘5*8’ or ‘a/b’ where ‘a’ and ‘b’ are variables. By default, the parameters are of IN type.

OUT Parameter:

This parameter is used for getting output from the subprograms. It is a read-write variable inside the subprograms. Their values can be changed inside the subprograms. In the calling statement, these parameters should always be a variable to hold the value from the current subprograms.

IN OUT Parameter:

This parameter is used for both giving input and for getting output from the subprograms. It is a read-write variable inside the subprograms. Their values can be changed inside the subprograms. In the calling statement, these parameters should always be a variable to hold the value from the subprograms.

These parameter type should be mentioned at the time of creating the subprograms.

RETURN

RETURN is the keyword that instructs the compiler to switch the control from the subprogram to the calling statement. In subprogram RETURN simply means that the control needs to exit from the subprogram. Once the controller finds RETURN keyword in the subprogram, the code after this will be skipped. Normally, parent or main block will call the subprograms, and then the control will shift from those parent block to the called subprograms. RETURN in the subprogram will return the control back to their parent block. In the case of functions RETURN statement also returns the value. The datatype of this value is always mentioned at the time of function declaration. The datatype can be of any valid PL/SQL data type. Note: Subprogram is nothing but a procedure, and it needs to be created manually as per the requirement. Once created they will be stored as database objects. Below are the characteristics of Procedure subprogram unit in PL/SQL:

Procedures are standalone blocks of a program that can be stored in the database. Call to these PLSQL procedures can be made by referring to their name, to execute the PL/SQL statements. It is mainly used to execute a process in PL/SQL. It can have nested blocks, or it can be defined and nested inside the other blocks or packages. It contains declaration part (optional), execution part, exception handling part (optional). The values can be passed into Oracle procedure or fetched from the procedure through parameters. These parameters should be included in the calling statement. A Procedure in SQL can have a RETURN statement to return the control to the calling block, but it cannot return any values through the RETURN statement. Procedures cannot be called directly from SELECT statements. They can be called from another block or through EXEC keyword.

Syntax:

CREATE PROCEDURE instructs the compiler to create new procedure in Oracle. Keyword ‘OR REPLACE’ instructs the compile to replace the existing procedure (if any) with the current one. Procedure name should be unique. Keyword ‘IS’ will be used, when the stored procedure in Oracle is nested into some other blocks. If the procedure is standalone then ‘AS’ will be used. Other than this coding standard, both have the same meaning.

Example1: Creating Procedure and calling it using EXEC In this example, we are going to create an Oracle procedure that takes the name as input and prints the welcome message as output. We are going to use EXEC command to call procedure. Code Explanation:

Code line 1: Creating the procedure with name ‘welcome_msg’ and with one parameter ‘p_name’ of ‘IN’ type. Code line 4: Printing the welcome message by concatenating the input name. Procedure is compiled successfully. Code line 7: Calling the procedure using EXEC command with the parameter ‘Guru99’. Procedure is executed, and the message is printed out as “Welcome Guru99”.

What is Function?

Functions is a standalone PL/SQL subprogram. Like PL/SQL procedure, functions have a unique name by which it can be referred. These are stored as PL/SQL database objects. Below are some of the characteristics of functions.

Functions are a standalone block that is mainly used for calculation purpose. Function use RETURN keyword to return the value, and the datatype of this is defined at the time of creation. A Function should either return a value or raise the exception, i.e. return is mandatory in functions. Function with no DML statements can be directly called in SELECT query whereas the function with DML operation can only be called from other PL/SQL blocks. It can have nested blocks, or it can be defined and nested inside the other blocks or packages. It contains declaration part (optional), execution part, exception handling part (optional). The values can be passed into the function or fetched from the procedure through the parameters. These parameters should be included in the calling statement. A PLSQL function can also return the value through OUT parameters other than using RETURN. Since it will always return the value, in calling statement it always accompanies with assignment operator to populate the variables.

Syntax

CREATE FUNCTION instructs the compiler to create a new function. Keyword ‘OR REPLACE’ instructs the compiler to replace the existing function (if any) with the current one. The Function name should be unique. RETURN datatype should be mentioned. Keyword ‘IS’ will be used, when the procedure is nested into some other blocks. If the procedure is standalone then ‘AS’ will be used. Other than this coding standard, both have the same meaning.

Example1: Creating Function and calling it using Anonymous Block In this program, we are going to create a function that takes the name as input and returns the welcome message as output. We are going to use anonymous block and select statement to call the function.

Code Explanation:

Code line 1: Creating the Oracle function with name ‘welcome_msg_func’ and with one parameter ‘p_name’ of ‘IN’ type. Code line 2: declaring the return type as VARCHAR2 Code line 5: Returning the concatenated value ‘Welcome’ and the parameter value. Code line 8: Anonymous block to call the above function. Code line 9: Declaring the variable with datatype same as the return datatype of the function. Code line 11: Calling the function and populating the return value to the variable ‘lv_msg’. Code line 12: Printing the variable value. The output you will get here is “Welcome Guru99” Code line 14: Calling the same function through SELECT statement. The return value is directed to the standard output directly.

Similarities between Procedure and Function

Both can be called from other PL/SQL blocks. If the exception raised in the subprogram is not handled in the subprogram exception handling section, then it will propagate to the calling block. Both can have as many parameters as required. Both are treated as database objects in PL/SQL.

Procedure Vs. Function: Key Differences

Built-in Functions in PL/SQL

PL/SQL contains various built-in functions to work with strings and date datatype. Here we are going to see the commonly used functions and their usage.

Conversion Functions

These built-in functions are used to convert one datatype to another datatype.

String Functions

These are the functions that are used on the character datatype. Select TO_NUMBER(‘1,234.45′,’9,999.99’) from dual; Output: 1234

Date Functions

These are functions that are used for manipulating with dates. Select INSTR(‘AEROPLANE’,’E’,2,2) from dual Output: 9 (2nd occurance of E) Select (‘my story’) from dual Output: My Story

Summary

In this chapter, we have learned the following.

How to create Procedure and different ways of calling it How to create Function and different ways of calling it Similarities and differences between Procedure and Function Parameters and RETURN common terminologies in PL/SQL subprograms Common built-in functions in Oracle PL/SQL