Stored Procedures in MySQL | Advanced MySQL Series

Summary

This lesson introduces stored procedures in SQL, emphasizing their utility for code reusability, performance enhancement, and simplification of complex queries. It demonstrates creating a simple stored procedure, 'large_salaries', and evolves to include multiple queries within a single procedure using delimiters. The tutorial also covers best practices, such as using parameters for input values, and provides a step-by-step guide on creating and calling stored procedures, including error handling and naming conventions.

Takeaways

• 📚 Stored procedures are SQL code saved for reuse, enhancing performance and simplifying complex queries.
• 🔍 The script demonstrates creating a simple stored procedure with a SELECT statement filtering salaries greater than or equal to 50,000.
• 💡 To create a stored procedure, use the 'CREATE PROCEDURE' statement, followed by a name and the SQL code to be executed.
• 👉 The script shows how to call a stored procedure using the 'CALL' statement and the procedure's name.
• 🚫 The script points out that placing multiple queries directly in a stored procedure without proper structure is not a best practice.
• 🔄 The use of 'delimiter' is introduced to separate multiple queries within a stored procedure, avoiding confusion and errors.
• 🛠️ The 'BEGIN ... END' block is used to group SQL statements within a stored procedure, with a custom delimiter marking the start and end.
• 🔧 It's recommended to change the delimiter back to a semicolon after the procedure to maintain normal SQL query operations.
• 🔄 The script explains how to modify an existing stored procedure using 'ALTER PROCEDURE' and the GUI approach in a database editor.
• 🔑 Parameters are introduced as variables within stored procedures, allowing input values to be passed and used in the procedure's code.
• 🔍 Parameters are defined with a name and data type, and can be used in the procedure's SQL statements to dynamically alter the query based on input.

Q & A

What is a stored procedure in SQL?

A stored procedure is a saved block of SQL code that can be executed repeatedly. It is used to store complex queries, simplify repetitive code, and enhance performance.

How do you create a simple stored procedure in SQL?

To create a simple stored procedure, you use the 'CREATE PROCEDURE' statement, followed by a name for the procedure and a closed parenthesis. Then, you can define the SQL code to be executed within the procedure.

What is the purpose of the 'CALL' statement in SQL?

The 'CALL' statement is used to invoke a stored procedure. It includes the name of the procedure and any necessary parameters, and it executes the SQL code defined within the procedure.

Why is it necessary to use a delimiter in stored procedures?

A delimiter is used to separate different SQL statements within a stored procedure. It prevents the SQL engine from confusing the end of one statement with the beginning of another, which can cause errors.

What is the best practice for creating a stored procedure that includes multiple queries?

The best practice is to use a delimiter to separate the queries and to enclose the procedure's SQL code within a 'BEGIN' and 'END' block, followed by the new delimiter to signify the end of the procedure.

How can you check if a stored procedure already exists before creating a new one?

You can use the 'IF EXISTS' clause before the 'CREATE PROCEDURE' statement to check if a stored procedure with the same name already exists. If it does, you can drop the existing procedure before creating a new one.

What is a parameter in the context of stored procedures?

A parameter in stored procedures is a variable that is passed as input to the procedure. It allows the stored procedure to accept an input value and use it within the SQL code.

How do you define a parameter in a stored procedure?

You define a parameter by specifying its name and data type within the 'CREATE PROCEDURE' statement, after the procedure name and before the SQL code block.

What is the benefit of using parameters in stored procedures?

Using parameters in stored procedures allows for greater flexibility and reusability of the code. It enables the same procedure to be used with different input values, making it more efficient and reducing code duplication.

How can you modify an existing stored procedure?

You can modify an existing stored procedure by using the 'ALTER PROCEDURE' statement, followed by the procedure name and the new SQL code that you want to include in the procedure.

What is the next topic that will be covered after stored procedures in the script?

The next topic to be covered after stored procedures is triggers and events in SQL.