Stored procedures in MySQL

A stored procedure is a section of a database that has been compiled and stored in advance SQL A collection of statements , Calling stored procedures can simplify a lot of work for application developers , Reduce data transfer between database and application server , It's good for improving the efficiency of data processing .
Stored procedures are very simple in mind , Database SQL Language level code encapsulation and reuse .

• characteristic
  1、 encapsulation , Reuse
  2、 Can receive parameters , You can also return data
  3、 Reduce network interaction , Efficiency tips
• establish

CREATE PROCEDURE  Stored procedure name ([ parameter list ])
BEGIN
	--SQL sentence 
END;

Be careful ： On the command line , Execute the procedure that created the stored procedure SQL when , You need to use keywords delimiter Appoint SQL The terminator of a statement .

• call
  CALL name ([ Parameters ]);
• see

# Query the stored procedure and status information of the specified database 
SELECT * FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_SCHEMA='xxx';
# Query the definition of a stored procedure 
SHOW CREATE PROCEDURE  Stored procedure name 

• Delete
  DROP PROCEDURE [IF EXISTS] Stored procedure name ;

Variable

• System variables
  The system variable is MySQL Provided by the server , It's not user-defined , At the server level . Divided into global variables （GLOBAL）、 Session variables （SESSION）.

see System variables

# See all system variables 
SHOW [SESSION | GLOBAL] VARIABLES;
# Can pass like Find variables by fuzzy matching 
SHOW [SESSION | GLOBAL] VARIABLES LIKE '...';
# View the specified variable 
SELECT @@[SESSION | GLOBAL]  System variable name ;

Set up System variables

SET [SESSION | GLOBAL]  System variable name = value ;
SET [SESSION | GLOBAL] System variable name = value ; 

Be careful ：
If not specified SESSION/GLOBAL, The default is SESSION, Session variables .
mysql After range restart , The global parameters set will become invalid , In order not to fail , Can be in /etc/my.cnf Middle configuration .

• User defined variables
  User defined variables are variables defined by users according to their needs , User variables need not be declared in advance , Use... Directly when using “@ Variable name ” Just use it . Its scope is the current session .

# assignment 
SET @var_name1=expr1[,@var_name2=expr2...];
SET @var_name1:=expr1[,@var_name2:=expr2...];# Recommended use 
SELECT @var_name:=expr1[,@var_name2:=expr2...];
SELECT  Field name  INTO @var_name FROM  Table name ;# Assign the value of the query in the table to the variable .

# Use 
SELECT @var_name;

Be careful ： User defined variables do not need to be declared or initialized , Only the obtained value is NULL.

• local variable
  A local variable is a variable that is defined as needed and takes effect locally , Before the visit , need DECLARE Statement . It can be used as local variables and input parameters in stored procedures , The scope of a local variable is in its declaration BEGIN …END block .

# Statement 
DECLARE  Variable name   Variable type  [DEFAULT ...];
# assignment 
SET  Variable name = value ;
SET  Variable name := value ;
SELECT  Field name  INTO  Variable name  FROM  Table name ...;

Variable types are database field types ：INT、BIGINT、CHAR、VARCHAR、DATE、TIME etc. .

if Judge

grammar ：

IF  Conditions 1 THEN
...
ELSEIF  Conditions 2 THEN # Optional 
...
ELSE # Optional 
...
END IF;

case

Grammar 1 ：

CASE case_value
	WHEN when_value1 THEN statement_list1
	[WHEN when_value2 THEN statement_list2]...
	[ELSE statement_list]
END CASE;

Grammar II ：

CASE
	WHEN search_condition1 THEN statement_list1
	[WHEN search_condition THEN statement_list2]...
	[ELSE statement_list]
END CASE;

while

while A loop is a conditional loop control statement . When the conditions are met , In the execution loop SQL sentence . The specific grammar is ：

# Judge the conditions first , If the condition is true, Then execute logic , otherwise , Do not execute logic 
WHILE  Conditions  DO
	SQL Logic ...
END WHILE;

repeat

repeat Is a conditional loop control statement , Exit the loop when the conditions are met . The specific grammar is ：

# First execute the logic , Then judge whether the logic meets , If meet , The exit . If not satisfied , Then go on to the next cycle 
REPEAT
	SQL Logic 
	UNTIL  Conditions 
END REPEAT;

loop

LOOP Implement a simple loop , If not SQL Add a condition to exit the loop in the logic , It can be used to realize a simple dead cycle .LOOP It can be used with the following two statements ：
LEAVE： In combination with recycling , Exit loop .
ITERATE： Must be used in the loop , The function is to skip the remaining statements of the current loop , Go directly to the next cycle .

[begin_label:] LOOP
	SQL Logic 
END LOOP [end_label];

LEAVE label; # Exit the loop body of the specified tag 
ITERATE label; # Go directly to the next cycle 

example ： take 1 To va1 Add even numbers between

create procedure p3(in va1 int)
begin
    declare va2 int default 0;
    sum:loop
        if va1 <= 0
            then leave sum;
        elseif va1%2=1
            then set va1 := va1 - 1;iterate sum;
        end if;
        set va2 := va2 + va1;
        set va1 := va1 - 1;
    end loop sum;
    select va2;
end;

The cursor

The cursor （CURSOR） Is the data type used to store the query result set , In stored procedures and functions, cursors can be used to cycle through the results . The use of cursors includes the declaration of cursors 、OPEN、FETCH and CLOSE, The grammar is as follows .

• declare cursor
  DECLARE Cursor name CURSOR FOR Query statement ;
• Open cursor
  PEN Cursor name ;
• Get cursor record
  FETCH Cursor name INTO Variable [, Variable ];
• Close cursor
  CLOSE Cursor name ;

Condition handler Handler

The condition handler can be used to define the corresponding processing steps when problems are encountered in the execution of the process control structure .
grammar ：

DECLARE handler_action HANDLER FOR condition_value [,condition_value]... statement;

handler_action
	CONTINUE: Continue with the current program 
	EXIT： Terminate the execution of the current program 
condition_value
	SQLSTATE sqlstate_vallue：   Status code , Such as 02000
	SQLWARNING：   Used to 01 At the beginning SQLSTATE Code abbreviation 
	NOT FOUND：   All with 02 At the beginning SQLSTATE Code abbreviation 
	SQLEXCEPTION：   All have not been SQLWARNING  or  NOT FOUND The captured SQLSTATE Code abbreviation 

example ： Get the name and major of the student in the student table .

create procedure p3(in uage int)
begin
    declare uname varchar(20);
    declare upro varchar(100);
    declare u_cursor cursor for select name,profession from tb_user where age <= uage;
    declare exit handler for not found close u_cursor;# Used to end the loop 
    drop table if exists tb_user_pro;
    create table if not exists tb_user_pro(
        id int primary key auto_increment comment ' Number ',
        name varchar(20) not null comment ' full name ',
        profession varchar(100) comment ' major '
    )comment ' Professional watch ';
    open u_cursor;
    while true do
        fetch u_cursor into uname,upro;
        insert into tb_user_pro value (null,uname,upro);
    end while;
    close u_cursor;
end;

Parameters

type	meaning	remarks
IN	This type of parameter is used as input , That is, when you need to call, pass in the value	Default
OUT	This type of parameter is used as output , That is, the parameter can be used as the return value
INOUT	It can be used as an input parameter , It can also be used as an output parameter

CREATE PROCEDURE  Stored procedure name ([IN/OUT/INOUT]  Parameter name   Parameter type )
BEGIN
...
END;

example ：85 The above points are excellent ,60~85 A pass ,60 The following are the failing grades