Stored procedures and functions (MySQL)

Catalog

One ： Overview of stored procedures

1.1 understand ：

1.2 classification ：

Two ： Create stored procedure

2.1 Syntax analysis ：

2.2 The code for ：

3、 ... and ： Calling stored procedure

3.2 The code for  

3.3 How to debug  

Four ： Storage function

4.1 Syntax analysis

4.2 Calling the storage function  

4.3 The code for

4.4 Compare stored functions with stored procedures  

5、 ... and . View of stored procedures and functions 、 modify 、 Delete  

5.1 see

5.2 modify

5.3 Delete

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One ： Overview of stored procedures

1.1 understand ：

meaning ：

The English of stored procedure is 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 .

And views 、 Comparison of functions ：

It has the same advantages as view , Clear 、 Security , It can also reduce the amount of network transmission . But it's different from the view , View is Virtual table , Usually do not directly operate on the underlying data table , and Stored procedures are programmed SQL, Sure Directly operate the underlying data table , Compared with the collection oriented operation , It can realize some more complex data processing .
Once the stored procedure is created , Using it is as simple as using a function , We can just call the stored procedure name directly . Compared to the function , The stored procedure is no return value Of .

1.2 classification ：

The parameter type of the stored procedure can be IN、OUT and INOUT. According to this classification is as follows ：

• 1、 No parameters （ No parameters, no return ）
• 2、 Just bring IN type （ No return with parameters ）
• 3、 Just bring OUT type （ No parameters return ）
• 4、 With both IN And bring OUT（ There are parameters and returns ）
• 5、 belt INOUT（ There are parameters and returns ）

Be careful ：IN、OUT、INOUT You can take more than one in one stored procedure .

Two ： Create stored procedure

2.1 Syntax analysis ：

grammar ：

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

Be similar to Java The method in ：

 Modifier   Return type   Method name ( Parameter type   Parameter name ,...){
  Method body ;
}

explain ：

1、 The meaning of the symbol before the parameter

• IN ： The current parameter is the input parameter , That is to say, the input parameter ; The stored procedure just reads the value of this parameter . If no parameter type is defined , The default is IN , Represents input parameter .
• OUT ： The current parameter is the output parameter , That is to say, it shows that ; After the execution is complete , The client or application calling the stored procedure can read the value returned by the parameter .
• INOUT ： The current parameter can be either an input parameter , It can also be an output parameter .

2、 The formal parameter type can be MySQL Any type in the database .
3、 characteristics Represents the constraint on the stored procedure specified when creating the stored procedure , The value information is as follows ：
 

LANGUAGE SQL
| [NOT] DETERMINISTIC
| { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
| SQL SECURITY { DEFINER | INVOKER }
| COMMENT 'string'

• LANGUAGE SQL ： Note that the stored procedure execution body is composed of SQL The sentences make up , The languages supported by the current system are SQL.
• [NOT] DETERMINISTIC ： Indicates whether the result of the stored procedure execution is determined .DETERMINISTIC Indicates that the result is certain . Every time a stored procedure is executed , The same input gets the same output .NOT DETERMINISTIC Indicates that the result is uncertain , The same input may get different outputs . If no value is specified , The default is NOTDETERMINISTIC.
• { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA } ： Indicates that the subroutine uses SQL Sentence restrictions .
• SQL SECURITY { DEFINER | INVOKER } ： Permission to execute the current stored procedure , That is, indicate which users can execute
  Row current stored procedure .
• COMMENT 'string' ： Annotation information , Can be used to describe stored procedures .

• CONTAINS SQL Indicates that the subroutine of the current stored procedure contains SQL sentence , But it doesn't contain read-write data SQL sentence ;
• NO SQL Indicates that the subroutine of the current stored procedure does not contain any SQL sentence ;
• READS SQL DATA Indicates that the subroutine of the current stored procedure contains read data SQL sentence ;
• MODIFIES SQL DATA Indicates that the subroutine of the current stored procedure contains data to be written SQL sentence .
• By default , The system specifies as CONTAINS SQL.

DEFINER Indicates that only the creator or definer of the current stored procedure can execute the current stored procedure ;
INVOKER Indicates that a user with access to the current stored procedure can execute the current stored procedure .
If the relevant value is not set , be MySQL The default specified value is DEFINER.
 

4、 There can be more than one in the stored procedure body SQL sentence , If only one SQL sentence , You can omit BEGIN and END
Writing stored procedures is not a simple thing , It is possible that the stored procedure requires complex SQL sentence .

1. BEGIN…END：BEGIN…END There are multiple statements in the middle , Each statement starts with （;） The sign is the Terminator .
2. DECLARE：DECLARE Used to declare variables , The position of use is BEGIN…END In the middle of the sentence , And it needs to be used before other statements
Declaration of line variables .
3. SET： Assignment statement , Used to assign values to variables .
4. SELECT… INTO： Store the query results from the data table into variables , That is, assign values to variables .

5、 You need to set a new end tag
DELIMITER： End of new tag

• because MySQL The default statement end symbol is semicolon ‘;’. To avoid problems with stored procedures SQL Statement terminator conflicts , Need to use DELIMITER Changes the end of a stored procedure .
• such as ：“DELIMITER //” The statement will MySQL Is set to //, And “END //” End stored procedure . After the stored procedure is defined, you can use “DELIMITER ;” Restore the default Terminator .DELIMITER You can also specify other symbols as endings .
• When using DELIMITER On command , Backslashes should be avoided （‘\’） character , Because the backslash is MySQL The escape character of .
   

2.2 The code for ：

give an example 1： Create stored procedure select_all_data(), see emps All data of table
 

DELIMITER $
CREATE PROCEDURE select_all_data()
BEGIN
 SELECT * FROM emps;
 
END $
DELIMITER ;

give an example 2： Create stored procedure avg_employee_salary(), Return the average salary of all employees
 

DELIMITER //
CREATE PROCEDURE avg_employee_salary ()
BEGIN
 SELECT AVG(salary) AS avg_salary FROM emps;
END //
DELIMITER ;

give an example 3： Create stored procedure show_max_salary(), To view “emps” The highest salary value in the table .
 

CREATE PROCEDURE show_max_salary()
 LANGUAGE SQL
 NOT DETERMINISTIC
 CONTAINS SQL
 SQL SECURITY DEFINER
 COMMENT ' View maximum salary '
 BEGIN
 SELECT MAX(salary) FROM emps;
 END //
DELIMITER ;

give an example 4： Create stored procedure show_min_salary(), see “emps” The minimum salary value of the table . And pass the minimum wage OUT Parameters “ms” Output

DELIMITER //
CREATE PROCEDURE show_min_salary(OUT ms DOUBLE)
 BEGIN
 SELECT MIN(salary) INTO ms FROM emps;
 END //
DELIMITER ;

give an example 5： Create stored procedure show_someone_salary(), see “emps” The salary of an employee in the table , And use IN Parameters empname Enter employee name .
 

DELIMITER //
CREATE PROCEDURE show_someone_salary(IN empname VARCHAR(20))
 BEGIN
 SELECT salary FROM emps WHERE ename = empname;
 END //
DELIMITER ;

give an example 6： Create stored procedure show_someone_salary2(), see “emps” The salary of an employee in the table , And use IN Parameters empname Enter employee name , use OUT Parameters empsalary Output employee salary .
 

DELIMITER //
CREATE PROCEDURE show_someone_salary2(IN empname VARCHAR(20),OUT empsalary DOUBLE)
 BEGIN
 SELECT salary INTO empsalary FROM emps WHERE ename = empname;
 END //
DELIMITER ;

give an example 7： Create stored procedure show_mgr_name(), Query the name of an employee leader , And use INOUT Parameters “empname” Enter employee name , Output the name of the leader .

DELIMITER //
CREATE PROCEDURE show_mgr_name(INOUT empname VARCHAR(20))
 BEGIN
 SELECT ename INTO empname FROM emps
 WHERE eid = (SELECT MID FROM emps WHERE ename=empname);
 END //
DELIMITER ;

3、 ... and ： Calling stored procedure

Stored procedures have a variety of calling methods . Stored procedures must use CALL The statement calls , And the stored procedure is related to the database , If you want to execute stored procedures in other databases , You need to specify a database name , for example CALL dbname.procname.

CALL  Stored procedure name ( Argument list )

Format ：

1、 call in Parameters of the pattern ：

CALL sp1(' value ');

2、 call out Parameters of the pattern ：

SET @name;
CALL sp1(@name);
SELECT @name;

3、 call inout Parameters of the pattern ：

SET @name= value ;
CALL sp1(@name);
SELECT @name;

3.2 The code for  

give an example 1：

DELIMITER //
CREATE PROCEDURE CountProc(IN sid INT,OUT num INT)
BEGIN
 SELECT COUNT(*) INTO num FROM fruits 
 WHERE s_id = sid;
END //
DELIMITER ;

Calling stored procedure ：

mysql> CALL CountProc (101, @num);
Query OK, 1 row affected (0.00 sec)

View return results ：

mysql> SELECT @num;

The stored procedure returns the specified s_id=101 The types of fruit offered by our fruit merchants , The return value is stored in num variable , Use SELECT see , The return result is 3.

3.3 How to debug  

stay MySQL in , Stored procedures are not like ordinary programming languages （ such as VC++、Java etc. ） There is a special integrated development environment . therefore , You can go through SELECT sentence , Query the intermediate results of program execution , To debug a SQL Statement correctness . After successful debugging , hold SELECT Move to the next... After the statement SQL After statement , Debug the next SQL sentence . such Step by step , You can complete the debugging of all operations in the stored procedure . Of course , You can also put... In a stored procedure SQL Copy the statement , Separate commissioning section by section .

Four ： Storage function

I learned a lot of functions earlier , Using these functions, you can perform various processing operations on data , Greatly improve the user's management efficiency of the database .MySQL Support for custom functions , Once defined , The calling method is the same as the calling method MySQL Like predefined system functions .

4.1 Syntax analysis

The functions I've learned ：LENGTH、SUBSTR、CONCAT etc.
Grammar format ：

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

explain ：

1、 parameter list ： The specified parameter is IN、OUT or INOUT Only right PROCEDURE It's legal. ,FUNCTION It always defaults to IN Parameters .
2、RETURNS type Statement represents the type of data returned by the function ;RETURNS Clause can only be used for FUNCTION Make a designation , For functions, this is mandatory Of . It is used to specify the return type of the function , And the body of the function must contain a RETURN value sentence .
3、characteristic The constraint on the function specified when creating the function . The value is the same as when creating the stored procedure , No more details here .
4、 The function body can also be used BEGIN…END To express SQL The beginning and end of the code . If the function body has only one statement , You can omit it BEGIN…END.

4.2 Calling the storage function  

stay MySQL in , How to use the storage function is the same as MySQL The use of internal functions is the same . In other words , User defined storage functions and MySQL The internal function is a property . The difference lies in , The storage function is User defined Of , And the inner function is MySQL Of Developer definition Of .

SELECT  Function name ( Argument list )

4.3 The code for

give an example 1：

Create a storage function , The name is email_by_name(), Parameter definition is null , This function queries Abel Of email, And back to , The data type is string .

DELIMITER //
CREATE FUNCTION email_by_name()
RETURNS VARCHAR(25)
DETERMINISTIC
CONTAINS SQL
BEGIN
 RETURN (SELECT email FROM employees WHERE last_name = 'Abel');
END //
DELIMITER ;

call ：

SELECT email_by_name();

give an example 2：

Create a storage function , The name is email_by_id(), Parameters of the incoming emp_id, This function queries emp_id Of email, And back to , The data type is string .

DELIMITER //
CREATE FUNCTION email_by_id(emp_id INT)
RETURNS VARCHAR(25)
DETERMINISTIC
CONTAINS SQL
BEGIN
 RETURN (SELECT email FROM employees WHERE employee_id = emp_id);
END //
DELIMITER ;

call ：

SET @emp_id = 102;
SELECT email_by_id(102);

give an example 3：

Create a storage function count_by_id(), Parameters of the incoming dept_id, This function queries dept_id Number of employees in the Department , And back to , The data type is integer .

DELIMITER //
CREATE FUNCTION count_by_id(dept_id INT)
RETURNS INT
 LANGUAGE SQL
 NOT DETERMINISTIC
 READS SQL DATA
 SQL SECURITY DEFINER
 COMMENT ' Query the average salary of the Department '
BEGIN
 RETURN (SELECT COUNT(*) FROM employees WHERE department_id = dept_id);
 
END //
DELIMITER ;

call ：

SET @dept_id = 50;
SELECT count_by_id(@dept_id);

Be careful ：

If an error is reported in creating a storage function “ you might want to use the less safe
log_bin_trust_function_creators variable ”, There are two ways to deal with it ：
The way 1： Add the necessary functional features “[NOT] DETERMINISTIC” and “{CONTAINS SQL | NO SQL | READS SQL DATA |MODIFIES SQL DATA}”

The way 2：mysql> SET GLOBAL log_bin_trust_function_creators = 1;（ Run this statement before creating the storage function ）

4.4 Compare stored functions with stored procedures  

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、 ... and . View of stored procedures and functions 、 modify 、 Delete  

5.1 see

After creation , How do we know the stored procedure we created 、 Is the storage function successful ？
MySQL It stores the state information of stored procedures and functions , Users can use SHOW STATUS Sentence or SHOW CREATE Statement to see , It can also be directly from the... Of the system information_schema Query in database . Here are 3 Methods .
 

1. Use SHOW CREATE Statement to view the creation information of stored procedures and functions
The basic grammatical structure is as follows ：

SHOW CREATE {PROCEDURE | FUNCTION}  Stored procedure name or function name 

give an example ：

SHOW CREATE FUNCTION test_db.CountProc \G

2. Use SHOW STATUS Statement to view the status information of stored procedures and functions

The basic grammatical structure is as follows ：

SHOW {PROCEDURE | FUNCTION} STATUS [LIKE 'pattern']

This statement returns the characteristics of the subroutine , Such as a database 、 name 、 type 、 Creator and date of creation and modification .
[LIKE 'pattern']： Matches the name of a stored procedure or function , It can be omitted . When omitted without writing , Will list MySQL Information about all stored procedures or functions that exist in the database . give an example ：SHOW STATUS Statement example , The code is as follows ：
 

mysql> SHOW PROCEDURE STATUS LIKE 'SELECT%' \G 
*************************** 1. row ***************************
                 Db: test_db
               Name: SelectAllData
               Type: PROCEDURE
             Definer: [email protected]
           Modified: 2021-10-16 15:55:07
             Created: 2021-10-16 15:55:07
       Security_type: DEFINER
             Comment: 
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8mb4_general_ci
1 row in set (0.00 sec)

3. from information_schema.Routines View the information of stored procedures and functions in the table
MySQL The information of stored procedures and functions is stored in information_schema Database based Routines In the table . You can query the information of stored procedures and functions by querying the records of the table . Its basic grammatical form is as follows ：

SELECT * FROM information_schema.Routines
WHERE ROUTINE_NAME=' The name of a stored procedure or function ' [AND ROUTINE_TYPE = {'PROCEDURE|FUNCTION'}];

explain ： If in MySQL The stored procedure and function names are the same in the database , It's better to designate ROUTINE_TYPE Query criteria to indicate whether the query is a stored procedure or a function .

give an example ： from Routines The query name in the table is CountProc Information about the storage function of , The code is as follows ：

SELECT * FROM information_schema.Routines
WHERE ROUTINE_NAME='count_by_id'　AND　ROUTINE_TYPE = 'FUNCTION' \G

5.2 modify

Modify stored procedures or functions , Does not affect stored procedure or function functions , Just modify the relevant features . Use ALTER Statements for .

ALTER {PROCEDURE | FUNCTION}  The name of a stored procedure or function  [characteristic ...]

among ,characteristic Specify the properties of the stored procedure or function , Its value information is the same as that of creating a stored procedure 、 The value information of function is slightly different .

{ CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
| SQL SECURITY { DEFINER | INVOKER }
| COMMENT 'string'

• CONTAINS SQL , Indicates that the subroutine contains SQL sentence , But does not contain statements that read or write data .
• NO SQL , Indicates that the subroutine does not contain SQL sentence .
• READS SQL DATA , A statement that contains read data in a subroutine .
• MODIFIES SQL DATA , Represents a statement in a subroutine that contains data to be written .
• SQL SECURITY { DEFINER | INVOKER } , Indicate who has authority to execute . among ,DEFINER , It means that only the definer himself can execute .INVOKER , Indicates that the caller can execute .
• COMMENT 'string' , Represents annotation information .

Modify stored procedures to use ALTER PROCEDURE sentence , Modify the storage function to use ALTER FUNCTION sentence . however , The structure of these two statements is the same , All parameters in the statement are the same .

give an example 1：

Modify stored procedure CountProc The definition of . Change the read and write permissions to MODIFIES SQL DATA, And indicate that the caller can execute , The code is as follows ：

ALTER　PROCEDURE　CountProc
MODIFIES SQL DATA
SQL SECURITY INVOKER ;

Query the modified information ：

SELECT specific_name,sql_data_access,security_type
FROM information_schema.`ROUTINES`
WHERE routine_name = 'CountProc' AND routine_type = 'PROCEDURE';

Results show , The stored procedure was modified successfully . From the results of the query, we can see , Access to data （SQL_DATA_ ACCESS） Has become a MODIFIES SQL DATA, Security type （SECURITY_TYPE） Has become a INVOKER.

give an example 2：

Modify storage function CountProc The definition of . Change the read and write permissions to READS SQL DATA, And add the comment information “FIND NAME”, The code is as follows ：

ALTER　FUNCTION　CountProc
READS SQL DATA
COMMENT 'FIND NAME' ;

Storage function modified successfully . From the results of the query, we can see , Access to data （SQL_DATA_ACCESS） Has become a READSSQL DATA, Function Comments （ROUTINE_COMMENT） Has become a FIND NAME.

5.3 Delete

Deletes stored procedures and functions , have access to DROP sentence , The syntax is as follows ：

DROP {PROCEDURE | FUNCTION} [IF EXISTS]  The name of a stored procedure or function 

IF EXISTS： If a program or function does not store , It can prevent errors , Make a use of SHOW WARNINGS View warnings for .
give an example ：

DROP PROCEDURE CountProc;

DROP FUNCTION CountProc;