MySQL stored procedure + function

Stored procedures and functions

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Variable

• System variables
• Global variables
• Session variables

 Look at all variables 

SHOW GLOBAL/SESSION VARIVALES

Conditions of the query

SHOW GLOBAL/SESSION LIKE '%char%'

View the value of a variable

SELECT @@GLOBAL/SESSION. System variable name

Set the value

SET GLOBAL/SESSION. System variable name = value ;

• Custom variable
• User variables

-  Scope ：  The target is valid for the current session 

-  Use 

  ```sql

  SET @ User variable name = value   # Declare assignments 1

  SELECT  Field  INTO @ Variable name  # Declare assignments 2

  SELECT @ Variable name  # see 

  ```

• local variable

-  Scope ： At present begin / end The scope is valid 

-  Use 

  ```mysql

  DECALARE  Variable name   type  ; # Statement 

  SET  Variable name = value ;# assignment 

  SELECT  Variable name ; # see 

  ```

stored procedure

• Concept

A set of precompiled SQL Statement set .

• benefits
• Improve the versatility of the code
• Simplified operation
• Reduced compilation and connection times , Increase of efficiency
• grammar
• establish

```sql

CREATE PROCEDURE  Stored procedure name ( parameter list )

BEGIN

	SQL sentence 1;

	SQL sentence 2;

END

```

-  parameter list 
  -  Parameter mode  IN,OUT,INOUT
  -  Parameter name 
  -  Parameter type 

• Use

```sql

CALL  Stored procedure name ( Argument list );

```

• Example
• Insert into book Five records in

```sql

# Definition 

CREATE PROCEDURE INSERT5()

BEGIN

    INSERT INTO book values (1,' computer network ',45.9,' Luo Guanzhong ',NOW());

    INSERT INTO book values (2,' computer network ',45.9,' Luo Guanzhong ',NOW());

    INSERT INTO book values (3,' computer network ',45.9,' Luo Guanzhong ',NOW());

    INSERT INTO book values (4,' computer network ',45.9,' Luo Guanzhong ',NOW());

    INSERT INTO book values (5,' computer network ',45.9,' Luo Guanzhong ',NOW());

END;

# call 

CALL INSERT5();

```

• Query employees according to salary

# Query employees according to salary

CREATE PROCEDURE getBySalary(IN s double)

BEGIN

  SELECT *

      FROM employees

          WHERE salary = s;

END;

# call

CALL getBySAlary();

• Return employee name according to salary

# Definition

CREATE PROCEDURE getNameBySalary(IN salary double,OUT name VARCHAR(20))

BEGIN

  SELECT last_name INTO name

      FROM employees

          WHERE employees.salary = salary;

END;

# call

SET @result;

CALL getNameBySalary(24000,@result);

SELECT @result;

function

There is and only one return

• establish

CREATE FUNCATION Function name ( Parameter name Parameter type , Parameter name Parameter type ) RETURNS Return type

BEGIN

The body of the function

END

• call

SELECT Function name ( parameter list );

Case presentation

1. Return without reference

  Number of employees returned to the company 

 ```sql

 # Definition 

 CREATE FUNCTION countEmp() RETURNS INT

 BEGIN

     DECLARE result INT;

     SELECT COUNT(*) INTO result

     FROM employees;

     RETURN result;

 END;

 # call 

 SELECT countEmp();

 ```

1. You can go back to

Return salary according to employee name

# Definition

CREATE FUNCTION getSalaryByName(name VARCHAR(20)) RETURNS DOUBLE

BEGIN

   DECLARE salary DOUBLE;

   SELECT e.salary INTO salary

   FROM employees e

   WHERE e.last_name = name;

   RETURN salary;

END;

# call

SELECT getSalaryByName('K_ing');

• View function definition statements

SHOW CREATE FUNCTION Function name ;

Process control structure

Branching structure

1. IF( expression 1, expression 2, expression 3) If the expression 1 establish , return 2, Otherwise return to 3
2. CASE structure If ELSE Omit When they don't match return NULL

# Equivalent judgment

CASE expression / value / Field

WHEN Constant 1 THEN sentence 1;

WHEN Constant 2 THEN sentence 2;

ELSE Default statement ;

END;

# Interval judgment

CASE

WHEN Conditions THEN sentence ;

WHEN Conditions THEN sentence ;

ELSE Default statement ;

END;

Case study : Create a function , According to the incoming grades , Display level

# Definition

CREATE FUNCTION wage_scale(score DOUBLE) RETURNS varchar(10)

BEGIN

   CASE

       WHEN score>=90 THEN RETURN ' good ';

       WHEN score>=80 THEN RETURN ' good ';

       WHEN score>=70 THEN RETURN ' Ordinary ';

       WHEN score>=60 THEN RETURN ' pass ';

       ELSE RETURN ' fail, ';

       END CASE;

END;

# call

SELECT wage_scale(90);

Loop structure

WHILE

• grammar

Tag name WHILE The loop condition DO

The loop body ;

END WHILE Tag name ;

Case study ： Insert in batches according to the number of times admin Table data

# Define stored procedures

CREATE PROCEDURE pro_while(IN count INT)

BEGIN

DECLARE i INT DEFAULT 1;

WHILE i <= count

DO

      INSERT INTO admin (username, password) VALUES (count, count);

      SET i = i + 1;

END WHILE;

end;

# call

CALL pro_while(10);

# result admin Insert in table 10 Data

LOOP It can be used to simulate a simple dead cycle

• grammar

Tag name LOOP

The loop body ;

END LOOP Tag name

REPEAT

• grammar

Tag name REPEAT

The loop body ;

UNTIL End cycle condition

END REPEAT Tag name

Case study

Known table content

Field	explain
id	Since the primary key
content	Random character

Create stored procedure , Inserts a specified number of random characters .

# Build table 
CREATE TABLE content(
    id INT PRIMARY KEY AUTO_INCREMENT,
    content VARCHAR(100)
);

# Create stored procedure 
CREATE PROCEDURE random_content(IN count INT)
BEGIN
    # Defining variables 
    DECLARE i INT DEFAULT 1;
    WHILE i <= count DO
        # The loop body 
        INSERT INTO content VALUES (null,random_bytes(100));
        SET i = i+1;
        END WHILE;
END;
#d
CALL random_content(100);

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