SQL - Stored Procedures

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SQL Stored Procedures

An SQL stored procedure is a group of pre-compiled SQL statements (prepared SQL code) that can be reused by simply calling it whenever needed.

It can be used to perform a wide range of database operations such as inserting, updating, or deleting data, generating reports, and performing complex calculations. Stored procedures are very useful because they allow you to encapsulate (bundle) a set of SQL statements as a single unit and execute them repeatedly with different parameters, making it easy to manage and reuse the code.

Procedures have similar structure as functions: they accept parameters and perform operations when we call them. But, the difference between them is that SQL stored procedures are simpler to write or create, whereas functions have a more rigid structure and support fewer clauses.

Syntax

The basic syntax to create an SQL stored procedure is as follows −

DELIMITER //
CREATE PROCEDURE procedure_name(parameter1 datatype, parameter2 datatype, ...)
BEGIN
   -- SQL statements to be executed
END
DELIMITER ;

• The CREATE PROCEDURE statement is used to create the procedure. We can define any number of input parameters as per the requirement.

• The SQL statements that make up the procedure are placed between the BEGIN and END keywords.

Creating a Procedure

We can create a stored procedure using the CREATE PROCEDURE statement in SQL. Following are the simple steps for creating a stored procedure −

• Choose a name for the procedure.

• Write the SQL code for the procedure.

• We can then test the stored procedure by executing it with different input parameters.

Example

To understand it better let us consider the CUSTOMERS table which contains the personal details of customers including their name, age, address and salary etc. as shown below −

CREATE TABLE CUSTOMERS (
   ID INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

Now, insert values into this table using the INSERT statement as follows −

INSERT INTO CUSTOMERS VALUES 
(1, 'Ramesh', 32, 'Ahmedabad', 2000.00),
(2, 'Khilan', 25, 'Delhi', 1500.00),
(3, 'Kaushik', 23, 'Kota', 2000.00),
(4, 'Chaitali', 25, 'Mumbai', 6500.00),
(5, 'Hardik', 27, 'Bhopal', 8500.00),
(6, 'Komal', 22, 'Hyderabad', 4500.00),
(7, 'Muffy', 24, 'Indore', 10000.00);

The table will be created as −

Now, let us look at a simple example of creating a stored procedure that takes an input parameter and returns a result set.

In the following query, we are creating the stored procedure with the name GetCustomerInfo. then we provide it with a single input parameter called @CutomerAge. The stored procedure then selects all records from the CUSTOMERS table where the value of the CutomerAge matches the input parameter.

DELIMITER //
CREATE PROCEDURE GetCustomerInfo(IN CustomerAge INT)
   BEGIN
      SELECT * FROM CUSTOMERS WHERE AGE = CustomerAge;
   END //
DELIMITER ;

Output

This would produce the following result −

Query OK, 0 rows affected (0.01 sec)

Verification

We can test the stored procedure by executing it using the CALL statement as shown below −

CALL GetCustomerInfo(25);

This will return all columns from the CUSTOMERS table where the customers age is 25.

Stored Procedure Parameter Types

Stored procedures in a database system can have different types of parameters, which are placeholders for values that will be passed to the stored procedure when it is executed. Following are the different types of stored procedure parameters in SQL −

Procedure with IN parameter

IN is the default parameter of the procedure that will receive input values. We can pass the values as arguments when the stored procedure is being called.

These values are read-only, so they cannot be modified by the stored procedure.

Example

In the following query, we are creating a stored procedure that takes a customer ID as an input parameter and returns the corresponding customer salary.

The procedure body simply performs a SELECT statement to retrieve the "Salary" column from the "CUSTOMERS" table, where the "CustomerID" matches the input parameter.

DELIMITER //
CREATE PROCEDURE GetCustomerSalary(IN CustomerID Int)
   BEGIN
      SELECT SALARY FROM CUSTOMERS WHERE ID = CustomerID;
   END //
DELIMITER ;

Output

This would produce the following result −

Query OK, 0 rows affected (0.01 sec)

Verification

We can test it by executing it with different ID as an input parameter as shown in the query below −

CALL GetCustomerSalary(6);

This will return the salary for the customer with an ID of 6, assuming there is a corresponding row in the CUSTOMERS table −

Procedure with OUT parameter

The OUT parameter is used to return the output value from the procedure.

Note that when using an OUT parameter, we must specify the keyword OUT before the parameter name when passing it to the stored procedure. This tells the SQL database that the parameter is an output parameter and should be assigned with a value in the stored procedure.

Example

In the following query we are creating a stored procedure that used to count the number of records of customer having same age and assign this count to the 'total' variable which holds the number of records.

The procedure body performs a SELECT statement to get the count of records having same age from the "CUSTOMERS" table

DELIMITER //
CREATE PROCEDURE GetDetail(OUT total INT)
   BEGIN
      SELECT COUNT(AGE) INTO total FROM CUSTOMERS
      WHERE AGE = 25;
   END //
DELIMITER ;

Calling the created procedure and passing the 'total' parameter

CALL GetDetail(@total);

Here, we are using the SELECT statement and getting the count −

SELECT @total;

Output

This would produce the following result −

Verification

To verify weather the procedure is created, we can use the following query −

SHOW CREATE PROCEDURE GetDetails;

Procedure with INOUT parameter

The INOUT parameter is a combination of an IN parameter and an OUT parameter. You can pass data into the stored procedure and receive data from the stored procedure using the same parameter.

To declare an INOUT parameter in a stored procedure, we need to specify the INOUT keyword before the parameter name.

Example

In the following query, we provide two INOUT parameters to the stored procedure: cust_id and curr_Salary. These two are used as both an input and output parameters.

The stored procedure first retrieves the current salary of the customer from the database using the cust_id parameter. It then increases the salary by 10% and updates the customers salary in the database using the same parameter.

DELIMITER //
CREATE PROCEDURE increaseSalary(INOUT Cust_Id Int,  INOUT curr_Salary Int)
   BEGIN
      SELECT SALARY INTO curr_Salary From CUSTOMERS Where ID = Cust_Id;
      SET curr_Salary = curr_Salary * 1.1;
      Update CUSTOMERS SET SALARY = curr_Salary Where ID = Cust_Id;
   END //
DELIMITER ;

Output

This would produce the following result −

Query OK, 0 rows affected (0.01 sec)

Verification

We can test it by executing it with different ID or input parameters as shown in the query below −

SET @customerID = 1;
SET @salary = 0.0;
CALL increaseSalary(@customerID, @salary);

Following is Query to select the updated salary from the stored procedure

SELECT @salary AS updated_salary;

The result-set is obtained as −

Advantages of Stored Procedures

Following are the advantages of stored procedures −

• Improved Performance: Stored procedures are pre-compiled and stored on the server, so they can be executed more quickly than SQL statements that are sent from client applications.

• Code Reuse: Stored procedures can be called from different client applications, which means that the same code can be reused across different applications. This reduces development time and maintenance costs.

• Reduced Network Traffic: Because stored procedures are executed on the server, only the results are returned to the client, which reduces network traffic and improves application performance.

• Better Security: Stored procedures can be used to enforce security rules and prevent unauthorized access to sensitive data. They can also limit the actions that can be performed by users, making it easier to maintain data integrity and consistency.

• Simplified Maintenance: By storing SQL code in a single location, it becomes easier to maintain and update the code. This makes it easier to fix bugs, add new functionality, and optimize performance.

Drawbacks of Stored Procedures

Following are the disadvantages of stored procedures −

• Increased Overhead: Stored procedures can consume more server resources than simple SQL statements, particularly when they are used frequently or for complex operations.

• Limited Portability: Stored procedures are often specific to a particular database management system (DBMS), which means they may not be easily portable to other DBMSs.

• Debugging Challenges: Debugging stored procedures can be more challenging than debugging simple SQL statements, particularly when there are multiple layers of code involved.

• Security Risks: If stored procedures are not written correctly, they can pose a security risk, particularly if they are used to access sensitive data or to perform actions that could compromise the integrity of the database.