MySQL stored procedure

summary

What is stored procedure ？

A stored procedure is a set of SQL Statements set , Powerful , It can realize some complex logic functions , It's the database SQL Language level code closure and reuse .

What are the characteristics ？

There are input and output parameters , You can declare variables , Yes IF、ELSE,while Wait for the control statement , By writing stored procedures , It can realize complex logic functions ; Common features of functions , modularization , encapsulation , Code using , Fast , Only the first execution needs to be compiled and optimized , Subsequent calls can be executed directly , Omit compilation .

Format

delimiter  Custom end symbol 
create procedure  Storage name ( [in, out, inout]  Parameter name   data type ...)
begin
	sql sentence 
end  Custom end symbol 
delimiter;

Example 1：

--  Example 1
delimiter $$
create procedure proname1()
begin
	select dname, ename from employee;
end $$
delimiter;

--  Calling stored procedure 
call proname1()

Variable

Direct variable ：

--  Variable 
delimiter $$
create procedure p2()
BEGIN
	declare var1 varchar(20) default 'aaa'; --  Create variables 
	set var1 = 'setname'; --  Assign a value to a variable 
	select var1; --  Output variables 
end $$;

delimter ;
call p2();

Query statement variables ：

You can also use select into Statement to assign a value to a variable , Query results can only output single row and single column .

select col_name [...] into val_name[,...]
from table_name where condition

Example ：

--  Query statement variables 
delimiter $$
create procedure p3()
BEGIN
	declare var2 varchar(20) default ''; --  Create variables 
	select ename into var2 from employee where eid = '1001'; --  Assign a value to a variable 
	select var2; --  Output variables 
end $$;
delimiter ;

call p3();

User variables

User customization , The current session is valid .

grammar ：

@var_name, There is no need to state in advance , Use to declare

Example ：

--  User variables 
delimiter $$
create procedure p4()
BEGIN
	set @var_name1 = 'litchi';
end $$
call p4() $$
select @var_name1 $$;

System variables

System variables are divided into global variables and session variables

The global variable is in MYSQL The startup time is automatically initialized by the server to the default value , These default values can be changed by my.ini This file to change .

Session variables every time a new connection is established , from MYSQL To initialize the ,MYSQL The values of all current global variables will be copied , As a conversation variable .

in other words , If you're building After the conversation , The values of session variables and global variables have not been changed manually , Then all the variable values are the same .

difference ：

The difference between a global variable and a session variable is , Changes to global variables affect the entire server , But changes to session variables , It only affects the current conversation （ That is, the current database connection ）

Global variables

Grammar format ：

@@global.var_name

The operation sample ：

--  Global variables 
show global variables;
--  View a global variable 
select @@global.auto_increment_increment;
--  Modify the value of the global variable 
set global sort_buffer_size = 40000; -- 262144
--  Query global variables 
select @@global.sort_buffer_size;

Session variables

--  Session variables 
show session variables;
--  View a session variable 
select @@session.auto_increment_increment;
--  Modify session variables 
set session sort_buffer_size = 60000;
--  View modification 
select @@session.sort_buffer_size;

​

Stored procedure parameters

IN key word

in Represents the parameter passed in , You can pass in values or variables , Even if you pass in a variable , Does not change the value of the variable , It can be updated internally , It only works within the scope of the function .

Example ：

--  Encapsulated with parameters   Stored procedure , Pass in the employee number , Find employee information 
delimiter $$
create procedure dec1(in param_eid varchar(20))
begin
	select * from employee where eid = param_eid;
end $$;
delimiter ;

call dec1(1001);

--  Example multi parameter 
delimiter $$
create procedure dec2(in param_dname varchar(20), in param_salary int(10))
begin
	select * from employee where dname = param_dname and salary > param_salary;
end $$;
delimiter ;

call dec2(' Shu Kingdom ', 5000);

OUT key word

out Efferent

Example ：

--  Pass in the employee number  , Return employee name 
delimiter $$
create procedure dec3(in param_eid int(10), out out_ename varchar(20) )
begin
	select ename into out_ename from employee where eid = param_eid;
end $$;
delimiter ;

call dec3(1001, @ename);
select @ename;

--  Pass in the employee number  , Return employee name and salary 
delimiter $$
create procedure dec4(in param_eid int(10), out out_ename varchar(20), out out_salary decimal(10,2) )
begin
	select 
		ename, salary into out_ename, out_salary
	from employee where eid = param_eid;
end $$;
delimiter ;

call dec4(1001, @ename, @salary);
select @ename;
select @salary;

INOUT

inout Indicates the parameter passed in from the outside Variables that can be returned after modification , That is, you can pass in the value of the variable or modify the value of the variable （ Even if the function is finished ）

Example ：

--  Pass in a number , Returns the of this number 10 times 
delimiter $$
create procedure dec5(inout num int)
begin
	set num = num * 10;
end $$
delimiter ;
set @inout_num = 20;
call dec5(@inout_num);
select @inout_num;

--  Incoming employees ID, Return department number , Salary , Annual salary 
delimiter $$
create procedure dec6(inout inout_ename varchar(20), inout inout_salay int(20) )
begin
	select concat_ws(",", eid, ename, salary ) into inout_ename from employee where ename = inout_ename;
	set inout_salay = inout_salay * 12;
end $$
delimiter ;

set @inout_ename = ' Liu bei ';
set @inout_salay= 3000;
call dec6(@inout_ename, @inout_salay);
select @inout_ename;
select @inout_salay;

Process control judgment

IF sentence

IF Statement contains multiple conditional judgments , According to the result TRUE, FALSE Execute statement ,

Grammar format ：

if search_condition then statement_list
	[elseif search_condition_2 then statement_list_2] ...
	[else statement_list_n]
end if

Code example ：

--  Example of control flow 1
delimiter $$
create procedure dec7(in score int)
BEGIN
	if score < 60
		then 
			select " fail, ";
	elseif score >= 60 and score < 90
		then 
			select " good ";
	elseif score >= 90 and score <= 100
		then 
			select " good ";
	ELSE
		select " Abnormal grades ";
	end if;
end $$
delimiter ;

set @score = 60;
call dec7(90)
select @score;

CASE sentence

--  grammar 1
case case_value
	when when_value then statement_list
	[when when_value then statement_list] ...
	[else statement_list]
end case

--  grammar 2
case 
	when search_condition then statement_list
	[when search_condition then statement_list] ...
	[else statement_list]
end case

Loop statement

while, repeat, loop

while Format

[ label ：] while  The loop condition  do
	 The loop body ：
end while [ label ]

Cycle control

leave similar break, Jump out of , End the current cycle

iterate Be similar to continue, continue , End this cycle and continue to the next

repeat

[ label :] repeat
	 Circular book ;
until  Conditional expression 
end repeat [ label ];

The cursor cursor

The cursor (cursor) Is the data type used to store the query result set , In stored procedures and functions, you can use the cursor to cycle the result set , The use of cursors includes the declaration of cursors 、OPEN、FETCH and CLOSE

Format ：

--  Declarative grammar 
declare cursor_name cursor for select_statement
--  Open syntax 
open cursor_name
--  Value Syntax 
fetch cursor_name into var_name [, var_name] ...
--  Turn off Syntax 
close cursor_name

exception handling