MySQL Learning notes （2）—— Stored procedures and stored functions

One 、 stored procedure

1. Concept ： Precompiled sql Collection of statements , Understand batch statements

2. benefits ;

1. Improved code reusability
2. Simplified operation
3. Reduce the number of compilations and the number of database servers , Improved efficiency

3. grammar ：

create procedure Stored procedure name （ Parameter mode Parameter name Parameter type ）
begin
Stored procedure body
end

4. parameter list ：

The parameter list consists of three parts ：
Parameter mode Parameter name Parameter type
give an example
in stuname varchar(32)

5. Parameter mode ：

in This parameter can be used as input , The caller needs to pass in the value
out This parameter can be used as output , It can be used as a return value
inout Change parameters and can be used as input 、 It can also be used as output

6. matters needing attention ：

1. If the stored procedure has only one sentence , that begin end It can be omitted
2. Each of the stored procedure bodies sql The result of the statement must be added with a semicolon ’;’
3. The result of the stored procedure can be used delemiter To reset
grammar ：
delimiter End mark
example ：delimiter //

7. Call syntax

call Stored procedure name （ Argument list ）;

8. actual combat

（1） Parameter list is empty

 practice ：
1. Bulk insert data 
DELIMITER //
CREATE PROCEDURE pro1()
BEGIN
	INSERT INTO stu(id,NAME) VALUES(NULL,'jack');
	INSERT INTO stu(id,NAME) VALUES(NULL,'tom');
	INSERT INTO stu(id,NAME) VALUES(NULL,'mike');
	INSERT INTO stu(id,NAME) VALUES(NULL,'rose');
END;
//

--  call 
CALL pro1();

SELECT * FROM stu;

（2） The parameter mode is in type ：

--  With parameters 
DELIMITER //
CREATE PROCEDURE pro2(IN t_name VARCHAR(32))
BEGIN
	SELECT * FROM stu WHERE NAME = t_name;
END;
//

--  call 
CALL pro2('jack');

SELECT * FROM stu;

DELIMITER //
CREATE PROCEDURE pro3(IN id INT,IN NAME VARCHAR(32))
BEGIN
	DECLARE result VARCHAR(32) DEFAULT '';
	
	SELECT COUNT(*)
	INTO result 
	FROM stu 
	WHERE stu.`id`=id AND stu.`name`=NAME;
	
	SELECT result; 
END;
//

--  call 
CALL pro3(15,'jack');

(3) The parameter list is out type

-- out type 
DELIMITER //
CREATE PROCEDURE pro4(IN id INT,OUT NAME VARCHAR(32))
BEGIN
	SELECT stu.`name`
	INTO NAME
	FROM stu 
	WHERE stu.`id`=id;
END;
//

--  call 
--  Define a variable to receive the return value 
CALL pro4(1,@name);
SELECT @name;

--  There are two out Type return value 
DELIMITER //
CREATE PROCEDURE pro5(IN id INT,OUT NAME VARCHAR(32),OUT age INT)
BEGIN
	SELECT stu.`name`,stu.`age`
	INTO NAME,age
	FROM stu 
	WHERE stu.`id`=id;
END;
//
--  call 
CALL pro5(1,@name2,@age);
SELECT @name2;
SELECT @age;
SELECT @name2,@age;

（4） Parameter type is inout type ：

--  Create a inout Stored procedure of mode parameters 

--  Pass in two values a and b, Final a and b All double and return 

DELIMITER //
CREATE PROCEDURE pro6(INOUT a INT,INOUT b INT)
BEGIN
	SET a=a*2;
	SET b=b*2;
END;

--  call 
SET @m=10;
SET @n=20;
CALL pro6(@m,@n);
SELECT @m,@n;
//

Other operations of stored procedures

Delete

Format ：DROP PROCEDURE Stored procedure name
Be careful ： Only one stored procedure can be deleted at a time

DELIMITER //
CREATE PROCEDURE pro7()
BEGIN
	SELECT * FROM stu;
END;
//

DROP PROCEDURE pro7;

Display stored procedure

Format ：SHOW CREATE PROCEDURE Stored procedure name

SHOW CREATE PROCEDURE pro6;

Be careful ：

The following operations are not supported
Don't allow desc
DESC PROCEDURE pro7;
Modify stored procedure （ I won't support it ）

Two 、 Storage function

1. The difference between stored procedure and stored function ：

Stored procedures can have 0 Return values , There can also be multiple return values , Suitable for bulk insertion , Batch update
function ： Yes and no 1 Return values , It is suitable to return a result after processing data

2. grammar

2.1 Create function syntax ：

CREATE FUNCTION  Function name （ parameter list ） RETURNS  Return type 
BEGIN
	 The body of the function 
END

Be careful ：
The parameter list contains two parts ： Parameter name Parameter type

The body of the function ：
Be sure to have return sentence , Otherwise, an error will be reported , It is suggested to put it at the end of the function body

When the function body has only one sentence , be begin end It can be omitted

2.2 Call syntax ：

SELECT  Function name （ parameter list ）

Execute statement , Get the return value

2.3 View functions

grammar ： SHOW CREATE FUNCTION The name of the function

SHOW CREATE FUNCTION fun2;

test

2.4 Delete function

grammar ：DROP FUNCTION Function name

DROP FUNCTION fun2;

2.5 matters needing attention ：

Functions are generally not modified

3. actual combat

3.1 No parameters return

 Return the number of students 

DELIMITER //
CREATE FUNCTION fun1() RETURNS INT
BEGIN
	DECLARE result INT DEFAULT 0;--  Variable declarations 
	SELECT COUNT(*) INTO result FROM stu;
	RETURN result;
END;
//

SELECT fun1();

SELECT * FROM stu;

3.2 There are parameters and return values

--  Return students according to their names id
DELIMITER //
CREATE FUNCTION fun2(sname VARCHAR(32)) RETURNS INT
BEGIN
	SET @a=0; --  Define a user variable 
	SELECT id
	INTO @a
	FROM stu
	WHERE NAME = sname; 
	
	RETURN @a;
END;
//

SELECT fun2('jack');

SELECT * FROM stu;

3.3 Small exercise

--  Create a function ： The implementation passes in two float, Return to the sum of the two 

DELIMITER //
CREATE FUNCTION num_sum(a FLOAT,b FLOAT) RETURNS FLOAT
BEGIN
	DECLARE result FLOAT DEFAULT 0;
	SET result = a + b;
	RETURN result;
END;
//

SELECT num_sum(1,2);

Conclusion

Level co., LTD. , It's hard to avoid mistakes , I hope you guys can knock ！