“@” symbol in stored procedure?

Question

I tried finding an answer to this online, but could not find any clear explanation:

Does the @ in a stored procedure serve some sort of special purpose/signify somet

Answer 1

The @variable syntax in MySQL denotes a user-defined session variable. You can set these user variables outside a stored procedure, but you can also set them inside a stored procedure, and the effect is that the variable retains the value after your procedure call returns.

So in your example, the following would also do the same thing:

CREATE PROCEDURE emp_count_2()
BEGIN
 SELECT COUNT(*) INTO @empCount FROM Employee;
END

CALL emp_count_2(); /* sets @empCount as a side-effect */
SELECT @empCount;

It's okay for multiple sessions to set the user variable in this way concurrently, because user variables are scoped to a single session, and concurrent sessions may have variables of the same name, but with different values.

The variable syntax with no @ prefix is for variables local to the procedure, either procedure parameters, or else local variables declared with DECLARE within the procedure body.

This usage you have, passing a user variable as a parameter and assigning it in the body of the procedure, is useful if you want to call a procedure several times and store the result in separate user variables. Otherwise each call to the procedure would overwrite the previous value in the @empCount user variable for the current session.