MySQL stored procedure in, out and inout parameter examples and summary

Stored Procedures

1. Create a stored procedure and view global variables

mysql> create database yy;
Query OK, 1 row affected (0.00 sec)

mysql> use yy;
Database changed
mysql> set @num1=10,@num2=20,@num3=30; //Set global variablesmysql> delimiter $$
mysql> create procedure p(in num1 int,out num2 int,inout num3 int)
 -> begin
 -> select num1,num2,num3;
 -> set num1=100,num2=200,num3=300;
 -> select num1,num2,num3;
 -> end $$
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter;
mysql> call p(@num1,@num2,@num3);

Summary 1:

• in and inout parameters pass the value of the global variable into the stored procedure, while out parameters do not pass the value of the global variable into the stored procedure. When using a stored procedure, the parameter values ​​in, out, and inout will change.
  

2. Changes in global variable values ​​when calling a stored procedure

mysql> select @num1,@num2,@num3;

Summary 2:

• After calling the stored procedure, it is found that the in parameter will not change the value of the global variable, while the out and inout parameters will change the value of the global variable after calling the stored procedure, and the value after the stored procedure reference will be assigned to the global variable.
  
• The in parameter assignment type can be a variable or a fixed value, while the out and inout parameter assignment types must be variables.

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