A case study of in, out and inout parameters of MySQL stored procedures
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Stored procedure
1. Create stored procedures and view global variables
two。 The change in the value of a global variable when calling a stored procedure
Stored procedure
1. Create stored procedures and view global variables
Mysql > create database yy;Query OK, 1 row affected (0.00 sec) mysql > use yy;Database changedmysql > set @ num1=10,@num2=20,@num3=30; / / set the global variable mysql > 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:
The in and inout parameters pass the value of the global variable into the stored procedure, while the out parameter does not pass the value of the global variable into the stored procedure. In the use of stored procedures, the parameter values in, out, and inout all change.
two。 The change in the value of a global variable when calling a stored procedure
Mysql > select @ num1,@num2,@num3
Summary 2:
When the stored procedure is called, 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 assign the referenced value of the stored procedure to the global variable.
The in parameter assignment type can be a variable and a fixed value, while the out and inout parameter assignment type must be a variable.
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