What is stored procedures in SQL?

Answer 1

What is a Stored Procedure?
A stored procedure is a prepared SQL code that you can save, so the code can be reused over and over again.

So if you have an SQL query that you write over and over again, save it as a stored procedure, and then just call it to execute it.

You can also pass parameters to a stored procedure, so that the stored procedure can act based on the parameter value(s) that is passed.

Go to this and read what it says:
https://www.w3schools.com/SQL/sql_stored_procedures.asp

Answer 2

What is a proprietary extension ?

Answer 3

vendor-specific and proprietary extensions for SQL are features that are outside the ISO standard for SQL.

MySQL is an SQL vendor.
Microsoft SQL Server is another vendor.
Oracle PL/SQL is another vendor.
PostgreSQL is another vendor.

How you define a stored procedure often depends on the specific vendor you're adding your stored procedures to. SQLite is a vendor that doesn't support stored procedures so you simply can't implement them in an SQLite database.

In other words, if you want to see examples of stored procedure implementations, you should look for a specific vendor like MySQL.
This explains it assuming you're using MySQL:
https://www.w3resource.com/mysql/mysql-procedure.php