MySQL stored procedure

Preface

MySQL 5.0 The version starts to support stored procedures .

stored procedure （Stored Procedure） It's a complex program stored in a database , A database object that can be called by an external program .

Stored procedures are designed to accomplish specific functions SQL Statements set , Compiled, created and stored in a database , The user can specify the name of the stored procedure and give the parameters ( When needed ) To call execution .

Stored procedures are very simple in mind , Database SQL Language level code encapsulation and reuse .

advantage

• Stored procedures can be encapsulated , And hide complex business logic .
• Stored procedures can return values , And can accept parameters .
• Stored procedures cannot be used SELECT Command to run , Because it's a subroutine , And view table , Data tables or user-defined functions are different .
• Stored procedures can be used for data validation , Enforce business logic, etc .

shortcoming

• stored procedure , Often customized to a specific database , Because the supported programming languages are different . When switching to the database system of other manufacturers , You need to rewrite the original stored procedure .
• Performance tuning and writing of stored procedures , Limited by various database systems .

First example

We use a simple example to learn the basic syntax of stored procedures
Basic grammar ：

CREATE PROCEDURE produce_name( parameter list )
beign --  Indicates the beginning of the process body  --
   --  Here is your business logic code  --
end --  Indicates the end of the process body  -- 

Case study ：
Let me start with a few questions , What I use here is Navicat.Navicat The default statement end symbol in is “;” But in a stored procedure, we may have multiple statements , Every statement ends with “;”, To prevent the creation of stored procedures Navicat Just use “;” As a closing sign , We need to restate the closing symbol ：

DELIMITER $$
 or 
DELIMITER //

tips : Of course, you can define this symbol yourself （ Don't be too casual ）.
Come on ！ Look at the case ：

--  Declaration end symbol  --
DELIMITER $$
CREATE PROCEDURE PROC_SELECT_BOO()
BEGIN --  Start  --
	SELECT * FROM book;
END $$ --  end  --
--  After declaring the end symbol back  --
DELIMITER ;

After execution, view the structure viewport on the left ：

Execute stored procedures ：

CALL PROC_SELECT_BOO;

Delete stored procedure ：

DROP PROCEDURE PROC_SELECT_BOOK

Of course, the stored procedure above just executes a query statement .
There can be business logic in stored procedures , Then basic process control is required .
So we have to write a certain quality of stored procedures , You need to understand some basic syntax of stored procedures .
tips： As long as you have learned programming , It's all very simple .
Of course , What makes us sick is , The syntax of stored procedures in each different database is different . This is also the biggest drawback of stored procedures mentioned earlier .

Basic grammar

Variable

MySQL The variables of are ： Global variables , Call back variables , User variables , System variables , local variable .
Here we focus on the use of stored procedures , For the time being, only local variables .
Local variables are declared in BEGIN and END Between variables , The scope is in BEGIN and END Between .
Declare variables ： Use DECLARE keyword

DECLARE var_name var_type [default_value]

Case study ：

CREATE PROCEDURE PROC_SELECT_BOOK()
BEGIN --  Start  --
	--  Declare variables  v_bookid  And the default value is 1 --
	DECLARE v_bookid int default 1;
	--  Use variables as query criteria  --
	SELECT * FROM book where bookid = v_bookid;
END $$ --  end  --

There are two ways to assign values to variables ：
The way 1： direct set

set v_bookid = 1;

The way 2： Use select into

select count(*) into v_count from book

Case study ：

• Local variables must be placed at the beginning of the stored procedure

--  Declaration end symbol  --
DELIMITER $$
CREATE PROCEDURE PROC_SELECT_BOOK()
BEGIN --  Start  --
	--  Declare variables  v_bookid  And the default value is 1 --
	DECLARE v_bookid int default 0;
	DECLARE v_count int;
	--  Use set Assign a value to a variable  --
	SET v_bookid = 1;
	--  Use select into  Assign a value to a variable  --
	SELECT count(*) into v_count FROM book where bookid = v_bookid;
END $$ --  end  --
--  After declaring the end symbol back  --
DELIMITER ;

Flow control statement

Branch statement

[1] if…then …else
grammar

--  Only if Structure  --
if  Conditions   then
  Executed statement 
end if;
--if.. else --
if  Conditions   then
 	if sentence 
else
	else sentence 
end if;
--  Multiple branches  --
if  Conditions   then
 	if sentence 
elseif  Conditions   then
	 sentence ...
	.....
else
	else sentence 
end if;

Case study ：

DELIMITER $$
CREATE PROCEDURE PROC_DEMO()
BEGIN
	DECLARE v_num int;
	set v_num = ROUND(RAND() * 10);
	IF MOD(v_num,2)=0 THEN
		select ' even numbers ';
	elseif MOD(v_num,3) = 0 THEN
		select '3 Multiple ';
	else
		select ' Odd number ';
	end if;
END $$
DELIMITER ;

[2]CASE structure
Serve directly ：

DELIMITER $$
CREATE PROCEDURE PROC_DEMO()
BEGIN
	DECLARE v_num int;
	set v_num = ROUND(RAND() * 10);
	CASE v_num
	when MOD(v_num,2)=0 THEN
		select ' even numbers ';
	when MOD(v_num,3)=0 THEN
		select '3 Multiple ';
	else
		select ' Odd number ';
	end case;
END $$
DELIMITER ;

Loop statement

[1]while ···· end while

while  Conditions  do
    -- The loop body 
endwhile

DELIMITER $$
CREATE PROCEDURE PROC_DEMO()
BEGIN
	DECLARE v_num int default 0;
	while v_num < 10 do
	insert into temp values(v_num);
	set v_num = v_num + 1;
	end while;
END $$
DELIMITER ;

[2]repeat···· end repeat

repeat
    -- The loop body 
until  The loop condition   
end repeat;

DELIMITER $$
CREATE PROCEDURE PROC_DEMO()
BEGIN
	DECLARE v_num int default 0;
	repeat
	insert into temp values(v_num);
	set v_num = v_num + 1;
	until v_num >= 10 end repeat;
END $$
DELIMITER ;

[3]loop ·····endloop

loop The loop does not require initial conditions , This and while Cyclic similarity , At the same time with repeat There is no end condition for a loop , leave The meaning of a sentence is to leave a loop .

DELIMITER $$
CREATE PROCEDURE PROC_DEMO()
BEGIN
	DECLARE v_num int default 0;
	LOOP_LABLE:loop 
	insert into temp values(v_num);
	set v_num = v_num + 1;
	if v_num >=10 then 
		leave LOOP_LABLE; 
	end if;
	end loop;
END $$
DELIMITER ;

Parameters of stored procedure

MySQL Parameters of stored procedure are used in the definition of stored procedure , There are three types of parameters ,IN,OUT,INOUT, In the form of ：

CREAT EPROCEDURE  Stored procedure name ([[IN |OUT |INOUT ]  Parameter name   Data classes ...])

• IN Input parameters ： Indicates that the caller passes a value... To the procedure （ The incoming value can be literal or variable ）
• OUT Output parameters ： Indicates that the procedure passes out a value to the caller ( Multiple values can be returned )（ Outgoing values can only be variables ）
• INOUT Input/output parameter ： It means that the caller passes in a value to the procedure , It also indicates that the procedure passes out a value to the caller （ Values can only be variables ）

1、in Input parameters

It can be simply understood as java Method parameters

delimiter $$
create procedure in_param(in p_in int)
begin
	select p_in;
	set p_in=2;
	select P_in;
end $$
delimiter ;

forehead ~~~~
To call a stored procedure with input parameters, you need to pass in the corresponding parameters

call in_param(100);

2、out Output parameters

Simply understood as java The return value of the method in

delimiter $$
create procedure out_param(out p_out int)
BEGIN
	select p_out;
	set p_out = 10000;
	select p_out;
end $$
delimiter ;

Call a stored procedure with output parameters

--  there @p_out  Is a user variable  --
set @p_out=1;
call out_param(@p_out);
select @p_out;

3、inout Input parameters

forehead ！！！ Literally . Can input , It can also output . In fact, it's good to know , Try not to use this type of parameter

delimiter $$
create procedure inout_param(out p_inout int)
BEGIN
	select p_inout;
	set p_inout = 10000;
	select p_inout;
end $$
delimiter ;

call

set @p_inout=1;
call inout_param(@p_inout);
select @p_inout;