What is the usage of “@” symbol in MySQL stored procedure?

The @ symbol in a stored procedure can be used for user-defined session variables. Let us first create a table −

mysql> create table DemoTable (    StudentName varchar(50) ); Query OK, 0 rows affected (1.30 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values('John Smith'); Query OK, 1 row affected (1.00 sec) mysql> insert into DemoTable values('John Doe'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values('Chris Brown'); Query OK, 1 row affected (0.53 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+-------------+ | StudentName | +-------------+ | John Smith | | John Doe | | Chris Brown | +-------------+ 3 rows in set (0.00 sec)

Let us now create a stored procedure to calculate the number of records from DemoTable −

mysql> DELIMITER // mysql> create procedure `Demo_Of_@Symbol`() BEGIN select count(*) into @numberOfRecords from DemoTable; END // Query OK, 0 rows affected (0.33 sec) mysql> DELIMITER ;

Following is the query to call the stored procedure using CALL command −

mysql> call `Demo_Of_@Symbol`(); Query OK, 1 row affected (0.00 sec)

Let us now see the usage of the @symbol −

mysql> select @numberOfRecords;

This will produce the following output −

+------------------+ | @numberOfRecords | +------------------+ | 3 | +------------------+ 1 row in set (0.00 sec)