The concepts and differences between MySQL stored procedures and stored functions, as well as how to create them, the role of delimiter, the viewing, modification, deletion of stored procedures and fu

1 summary

1.1 stored procedure

• Its idea is very simple , It's just a group of people passing through Precompile Of SQL Encapsulation of statements .
• Execution process ： Stored procedures are pre stored in MySQL Server , When it needs to be implemented , The client only needs to issue a command to the server to call the stored procedure , The server side can store the pre stored series SQL Execute all statements .

1.2 Storage function

MySQL Support for custom functions , Once defined , The calling method is the same as the calling method MySQL Like predefined system functions .

2 establish

2.1 Create stored procedure

2.1.1 grammar

CREATE PROCEDURE  Stored procedure name  (IN | OUT | INOUT  Parameter name   Parameter type ,...)
[characteristics ...]
BEGIN 
 Stored procedure body 
END

2.1.2 Parameter list

• No parameters （ No parameters, no return ）
• Just bring IN type （ No return with parameters ）
• Just bring OUT type （ No parameters return ）
• With both IN And bring OUT（ There are parameters and returns ）
• belt INOUT（ There are parameters and returns
  Be careful ：IN、OUT、INOUT You can take more than one in one stored procedure .

2.1.3 Code

--  Create an empty parameter stored procedure 
	CREATE PROCEDURE select_all_data () 
	BEGIN
		SELECT
			* 
		FROM
		employees;
	END;
--  Calls to stored procedures 
CALL select_all_data();


--  Create a OUT stored procedure 
CREATE PROCEDURE show_min_salary ( OUT ms DOUBLE ) BEGIN
	SELECT
		min( salary ) INTO ms 
	FROM
	employees;
END;
--  Calls to stored procedures 
--  Define a variable to store the result 
CALL show_min_salary(@ms);
--  View variable values 
SELECT @ms;


--  Create a IN stored procedure 
CREATE PROCEDURE show_someone_salary ( IN emp_name VARCHAR(20) ) 
BEGIN
	SELECT
		salary 
	FROM
		employees 
	WHERE
		last_name = emp_name;
END;
--  The calling method of stored procedure I 
CALL show_someone_salary('King');
--  The calling method of stored procedure I 
SET @emp_name  = 'King';
CALL show_someone_salary(@emp_name);


--  Create a IN and OUT Stored procedure 
CREATE PROCEDURE show_someone_salary2 ( IN empname VARCHAR ( 20 ), OUT empsalary DOUBLE ) 
BEGIN
	SELECT
		salary INTO empsalary 
	FROM
		employees 
	WHERE
		last_name = empname;
END;
--  How to call stored procedures 
CALL show_someone_salary2('Kochhar',@empsalary);
SELECT @empsalary;


--  Create a INOUT Stored procedure 
CREATE PROCEDURE show_mgr_name (
	INOUT empname VARCHAR ( 20 )) 
BEGIN
	SELECT
		last_name INTO  
	FROM
		employees 
	WHERE
	manager_id = ( SELECT employee_id FROM employees WHERE last_name = empname );
END;
--  How to call stored procedures 
SET @emp_name = 'De Haan';
CALL show_mgr_name(@emp_name);
SELECT @emp_name;

2.2 Create a storage function

2.2.1 grammar

CREATE FUNCTION  Function name ( Parameter name   Parameter type ,...)
RETURNS  return type 
[characteristics]
BEGIN
	 The body of the function  # There must be... In the body of the function return sentence 
END;

2.2.2 Code

--  Method 1 of creating null parameter function 
CREATE FUNCTION email_by_name()
RETURNS VARCHAR(25)--  Parameter type returned 
--  solve you might want to use the less safe log_bin_trust_function_creators variable problem 
				DETERMINISTIC
				CONTAINS SQL
				READS SQL DATA
BEGIN
	RETURN (SELECT email FROM employees WHERE last_name = 'Abel');
END;


 --  Method 2 of creating null parameter function 
SET GLOBAL log_bin_trust_function_creators = 1; --  solve you might want to use the less safe log_bin_trust_function_creators variable error 
CREATE FUNCTION email_by_name2()
RETURNS VARCHAR(25)
BEGIN
	RETURN (SELECT email FROM employees WHERE last_name = 'Abel');
END;
--  Function call 
select email_by_name();


 --  Create a parametric function 
 CREATE FUNCTION email_by_id(emp_id INT)
 RETURNS VARCHAR(25)
 BEGIN
		RETURN (SELECT email FROM employees WHERE employee_id = emp_id);
 END;
 --  Call function 

3 delimiter The role of

--  Modify the ending character as &
DELIMITER &
--  Modify the ending character as ;
DELIMITER ;

4 The difference between stored procedure and stored function

Besides , Storage functions can be used in query statements , Stored procedures don't work . conversely , Stored procedures are more powerful , Including the ability to perform operations on tables （ For example, create a table , Delete tables, etc ） And transaction operations , These functions are not available in storage functions .

5 Error resolution when creating function

error ：

you might want to use the less safe log_bin_trust_function_creators variable

solve ：

• Mode one : Add the necessary functional features “[NOT] DETERMINISTIC” and “[CONTAINS SQL|NO SQL|READS SQL DATA|MODIFIES SQL DATA}"
• Mode two ： SET GLOBAL log_bin_trust_function_creators = 1;

6 View of stored procedures and functions 、 modify 、 Delete

6.1 see

-- 1. Use show create Statement to view the creation information of stored procedures and functions 
--  View stored procedures 
SHOW CREATE PROCEDURE show_mgr_name;
--  View functions 
SHOW CREATE FUNCTION email_by_id;

-- 2. Use show status Statement to view the state information of stored procedures and functions 
--  View stored procedures 
SHOW PROCEDURE STATUS LIKE 'show_mgr_name';
--  View functions 
SHOW FUNCTION STATUS LIKE 'email_by_id';

-- 3. from information_schema.Routines View the information of stored procedures and functions in the table 
SELECT * FROM information_schema.Routines WHERE ROUTINE_NAME = ' Stored procedure name or function name ';
--  When duplicate names, specify whether the type is a function or a stored procedure 
SELECT * FROM information_schema.Routines WHERE ROUTINE_NAME = 'show_mgr_name' AND ROUTINE_TYPE = 'PROCEDURE';

6.2 modify

ALTER PROCEDURE show_max_salary SQL SECURITY INVOKER COMMENT ' Query maximum wage ';

6.3 Delete

DROP PROCEDURE  Stored procedure name ;
DROP FUNCTION  Function name ;

7 Advantages and disadvantages of the storage process

7.1 advantage

• Stored procedures can be compiled and used more than once . Stored procedures are compiled only at creation time , There is no need to recompile later , That's a step up SQL Efficiency of execution .
• It can reduce the development workload . Encapsulating code into modules , It's actually one of the core ideas of programming , In this way, complex problems can be broken down into different modules , And then the modules can be reused , While reducing development effort , It also keeps the structure of the code clear .
• The security of stored procedure is strong . When we set the stored procedure, we can set the user's permission , This is as secure as the view .
• It can reduce the amount of network transmission . Because the code is encapsulated in stored procedures , Each time you use it, you just need to call the stored procedure , This reduces the amount of network traffic .
• Good encapsulation . When performing relatively complex database operations , We used to use one by one SQL sentence , Operations that may require multiple database connections to complete , Now it's a stored procedure , Just connect once .

7.2 shortcoming

• Poor portability . Stored procedures cannot be migrated across databases , For example MySQL、Oracle and SQLServer Stored procedures written in , It needs to be rewritten when changing to other databases .
• Debugging difficulty . Only a few DBMS Supports debugging of stored procedures . For complex stored procedures , Development and maintenance are not easy . Although there are some third-party tools that can debug stored procedures , But there's a charge .
• Version management of stored procedures is difficult . For example, the index of the data table has changed , Can cause stored procedures to fail . We often need version management when we develop software , But the stored procedure itself has no version control , It's troublesome to update the version iteratively .
• It is not suitable for high concurrency scenarios . High concurrency scenarios need to reduce the pressure on the database , Sometimes the database will adopt the way of dividing database and table , And it's very scalable , under these circumstances , Stored procedures can become difficult to maintain , Increase the pressure on the database , Obviously not .