MySQL | store notes of Master Kong MySQL from introduction to advanced

Sort it out again , It is also a process of digestion . Learning must focus on input and output , If you only enter , Most of the time, it's just the brain that understands now , But did not remember . In this way, when actually doing questions or applying , There is no way to write .

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Storage Stored

stored procedure and Storage function Sure The complex SQL Logic encapsulated together , Applications There is no need to pay attention to the complex inside of stored procedures and functions SQL Logic , Simply call stored procedures and functions .

1. stored procedure PROCEDURE

thought

• A group passed 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 .

advantage ：

• It can be compiled and used more than once —— Reduce developer stress
• Good encapsulation —— Reduce mistakes , Increase of efficiency
• Reduce network traffic
• The security of stored procedure is strong —— Reduce SQL The risk of statement exposure

shortcoming ：

• Poor portability
• Debugging difficulty
• Version management of stored procedures is difficult
• Not suitable for high concurrency scenarios

Use

• As simple as using functions

The stored procedure did not return a value

（1） Create stored procedure

DELIMITER $  --  New end tag 

CREATE PROCEDURE  Stored procedure name (IN|OUT|INOUT  Parameter name   Parameter type , IN|OUT|INOUT  Parameter name   Parameter type , ...)

	[characteristics ...]  --  Constraints on stored procedures 
	--LANGUAGE SQL
	--| [NOT] DETERMINISTIC
	--| { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
	--| SQL SECURITY { DEFINER | INVOKER } --  Security level （ The definer can call  |  If you have permission, you can call ）, The default is DEFINER
	--| COMMENT 'string'

	BEGIN
		 Query statement 
	END $

DELIMITER ;  --  Restore end tag 

• Two common end tags ：$、//
• SET： Assignment statement , Assign values to variables .
• SELECT INTO： Store the query result of the assignment statement in the variable , That is, assign values to variables .
• Five input parameters

  ① No parameters （ No parameters, no return ）
  ②IN（ Returned by parameter none ）
  ③OUT（ No parameters return ）
  ④IN and OUT（ There are parameters and returns ）
  ⑤INOUT（ There are parameters and returns ）

（2） Calling stored procedure

CALL  Stored procedure name ( Argument list )

（3） View stored procedures

① View the... Of the stored procedure Create information

SHOW CREATE PROCEDURE  Stored procedure name 

② View the... Of the stored procedure State information

SHOW PROCEDURE STATUS [LIKE '...']

（4） Modify stored procedure

ALTER PROCEDURE  Stored function name 

（5） Delete stored procedure

DROP PROCEDURE IF EXIST  Stored function name ;

2. Storage function FUNCTION

• be used for Inquire about

• There is and only one return value

（1） Create a storage function

DELIMITER //

CREATE FUNCTION  Stored function name ( Parameter name ,  Parameter type )
	RETURNS  return type 
			#  In order to avoid reporting mistakes , You need to add the following three lines 
	        DETERMINISTIC  --
	        CONTAINS SQL --  contain SQL
	        READS SQL DATA
	
	BEGIN
		RETURN(SELECT Query statement );
	END //

DELIMITER;  -- Reset the end symbol to `;`

or

#  To avoid error reporting , Need to add this sentence 
SET GLOBAL log_bin_trust_function_creators = 1;

DELIMITER //

CREATE FUNCTION  Stored function name ( Parameter name 1  Parameter type ,  Parameter name 2  Parameter type , ...)
	RETURNS  return type 

	BEGIN
		RETURN(SELECT Query statement );
	END //

DELIMITER;  -- Reset the end symbol to `;`

（2） Calling the storage function

SELECT  Stored function name ();  --  Call function 

SET @emp_id := 102;  --  Defining variables 
# SET @emp_id = 102; `:=` and `=` Fine 
SELECT  Stored function name (@emp_id);  -- Call function 

Ingenious notes ： because Storage function Applicable to query , So call it with SELECT .

（3） Look at the storage functions

① View the storage function Create information

SHOW CREATE FUNCTION  Stored function name 

② View the storage function State information

SHOW FUNCTION STATUS [LIKE '...']

（4） Modify storage function

ALTER FUNCTION  Stored function name 

（5） Delete storage function

DROP FUNCTION IF EXIST  Stored function name ;

Stored supplemental knowledge

1. Variable

Both assignment symbols are OK , The effect is the same

• =
• :=

（1） System variables

The system variable uses @@ start

Two default values

• compile MySQL The default value of the parameter
• my.iniMySQL Parameter values in the configuration file

Modify the value of the system variable

• stay MySQL During service operation , Use SET Command to reset the value of the system variable .
• modify my.iniMySQL The configuration file , Then modify MySQL The value of the system variable （ This method needs to be restarted MySQL service ）

The default is Session system variables

① Global system variables （ abbreviation ： Global variables ）

global keyword

• max_connections： Only global system variables , Limit the maximum number of connections to the server
• See all global variables SHOW GLOBAL VARIABLES;
• View some global variables that meet the conditions SHOW GLOBAL VARIABLES LIKE '% identifier %';
• View the specified global variables SELECT @@global. Variable name ;

Assign values to global variables

• The way 1

  SELECT @@global. Variable name ;
  SET GLOBAL  Variable name = A variable's value ;
  

• The way 2

  SELECT @@global. Variable name ;
  SET @@global. Variable name = A variable's value ;
  

② Session system variables （ abbreviation ：local Variable ）

session keyword

• The initial value of the session system variable is the copy of the global system variable value .

• pseudo_thread_id： Can only be applied to the current session , Used to mark the current session MySQL Connect ID.

• View all session variables SHOW SESSION VARIABLES; or SHOW VARIALBLES;（ because Variable The default is Session system variables ）

• Look at some session variables that meet the criteria SHOW SESSION VARIABLES LIKE '% identifier %';

• View specified session variables SELECT @@session. Variable name ; or SELECT @@ Variable name ;

Assign values to session variables

• The way 1

  SELECT @@session. Variable name ;
  SET SESSION  Variable name = A variable's value ;
  

• The way 2

  SELECT @@session. Variable name ;
  SET @@session. Variable name = A variable's value ;
  

（2） User defined variables

User defined variables use @ start ： Session user variables （ Don't specify the type ）, local variable （ You need to specify the type ）

① Session user variables

• Definition and assignment （ Need to add @, There is no need to specify the type ）
  1. Manual assignment

  SET @ User variables  =  value ;
  SET @ User variables  :=  value ;
  

  2. Fu Field values in the table

  SELECT @ User variables  :=  expression  [FROM  Wait for words ];
  SELECT  expression  INTO @ User variables  [FROM  Wait for words ];
  

• Scope
  Only valid for the current session
  Can be added anywhere in the conversation

• View user variables

  SELECT @ User variables 
  

② local variable

• Definition （ Type required ）

  DECLARE  Local variable name   type  [default  value ];
  #  without default Clause , The initial value is NULL
  

• assignment （ No need to add @）
  1. Manual assignment

  SET  Variable name = value 
  SET  Variable name := value 
  

  2. Fu Field values in the table

  SELECT  Field name or expression  INTO  Variable name  FROM  surface ;
  

• Scope

  Only in BEGIN and END Sentence block Effective in , And can only be placed in The first sentence .
  Can only be used in stored procedures and functions

• Using variables

  SELECT  Local variable name 
  

DELIMITER //

CLEAR PROVEDURE/FUNCTION  Stored procedure name / Stored function name 

BEGIN
	#  Declare local variables 
	DECLARE  Local variable name   type  DEFAULT  The default value is ;

	#  Assign values to local variables 
	SET  Local variable name  =  value ;
	SELECT  Field name  INTO  Local variable name  FROM  Table name  WHERE  filter ;
	
	#  View the value of a local variable 
	SELECT  Variable 1,  Variable 2, ...;
END

DELIMITER ;

2. “ abnormal ” Handle

In order to avoid stopping the program when it reports an error , You can list the possible errors , When an error occurs , Only report the corresponding error code , And ensure that the program can be successfully executed .

（1） Defined conditions

namely ： to Implementation defines the problems that may be encountered during program execution name . Will a Wrong name and Specified error condition Connect .

# MySQL_error_code
DECLARE  Error name  CONDITION FOR  Numeric type error code 

# sqlstate_value
DECLARE  Error name  CONDITION FOR SQLSTATE  String type error code 

example ： stay ERROR 1418(HY000) in ：

1418 yes MySQL_error_code（ Numeric type error code ）,
HY000 yes sqlstate_value（ The length is 5 String type error code ）

DECLARE field_Not_Be_NULL CON

（2） The handler

namely ： Define what you should do when you encounter a problem , Guarantee Stored procedure or function Continue to execute in case of warnings or errors .

• Enhance the ability of stored programs to deal with problems , Avoid abnormal program stop .

DECLARE  Processing mode  HANDLER FOR  Wrong type   Processing statements 

Processing mode

• CONTINUE： Encounters an error Don't deal with , Carry on .
• EXIT： Encounters an error Quit now

Wrong type

• SQLSTATE ‘ String error code ’： The length is 5 Of sqlstate_value Error code for type
• MySQL_error_code： Match numeric type error code
• Wrong name ： Express DECLARE...CONDITION Defined error condition name
• SQLWARNING ： Match all to 01 At the beginning SQLSTATE Error code ;
• NOT FOUND ： Match all to 02 At the beginning SQLSTATE Error code ;
• SQLEXCEPTION ： Match all that have not been SQLWARNING or NOT FOUND The captured SQLSTATE Error code ;

Processing statements
SET Variable = value

BEGIN...END

Several ways to define handlers , The code is as follows ：

# Method 1： Capture sqlstate_value
DECLARE CONTINUE HANDLER FOR SQLSTATE '42S02' SET @info = 'NO_SUCH_TABLE';

# Method 2： Capture mysql_error_value
DECLARE CONTINUE HANDLER FOR 1146 SET @info = 'NO_SUCH_TABLE';

# Method 3： Define the conditions first , Call again 
DECLARE no_such_table CONDITION FOR 1146;
DECLARE CONTINUE HANDLER FOR NO_SUCH_TABLE SET @info = 'NO_SUCH_TABLE';

# Method 4： Use SQLWARNING
DECLARE EXIT HANDLER FOR SQLWARNING SET @info = 'ERROR';

# Method 5： Use NOT FOUND
DECLARE EXIT HANDLER FOR NOT FOUND SET @info = 'NO_SUCH_TABLE';

# Method 6： Use SQLEXCEPTION
DECLARE EXIT HANDLER FOR SQLEXCEPTION SET @info = 'ERROR';

3. Process control

（1） Conditional statements IFCASE

①IF

Use in BEGIN...END in

DELIMITER //

CREATE PROCEDURE/FUNCTION  Stored procedure name / Stored function name ()

	[ Tagnames :]BEGIN
	
		IF ...
			THEN ...  -- LEAVE  Tagnames 
		ELSEIF ...
			THEN ...
		ELSE
		END IF;
	
	END //

DELIMITER ;

②CASE

be used for BEGIN...END in

• situation 1（ Similar to switch）

  CASE  expression 
  WHEN  value 1 THEN  result 1 Or words 1( sentence 1 Add... To the end of ;)
  WHEN  value 2 THEN  result 2 Or words 2( sentence 1 Add... To the end of ;)
  ...
  ELSE  result n Or words n( sentence n Add... To the end of ;)
  END CASE
  

• situation 2（ Similar to multiple IF）

  CASE 
  WHEN  Conditions 1 THEN  result 1 Or words 1( sentence 1 Add... To the end of ;)
  WHEN  Conditions 2 THEN  result 2 Or words 2( sentence 1 Add... To the end of ;)
  ...
  ELSE  result n Or words n( sentence n Add... To the end of ;)
  END CASE
  

（2） Loop statement LOOPWHILEREPEAT

All three loops can omit the name .
But if you add a loop control statement to the loop （LEAVE or ITERATE）, be You must add a name .

①LOOP（ Generally used to implement simple " die " loop .（ Usually in combination with LEAVE Use ））

DELIMITER //

CREATE PROCEDURE/FUNCTION  Stored procedure name / Stored function name ()

BEGIN

	#  Defining variables , Used to record the number of cycles 
	DECLARE loop_count INT DEFAULT 0;

	# ① Initialize the loop condition 
	SELECT ...

	[ Tagnames :]Loop

		# ② The loop condition （ When to end the cycle ）
		[IF ... THEN LEAVE [ Tagnames ];
		END IF;]
		[IF ... THEN ITERATE [ Tagnames ];
		END IF;]
		# ③ The loop body —— Cycle through the tasks to be completed 
		... --  Write... According to the requirements of the topic 
		
		# ④ Iteration conditions 
		...;  --  Recalculate the cycle condition （ Consistent with initialization cycle conditions ）
		
		SET loop_count = loop_count +1;  --  cycles +1

	END LOOP loop name ;
	
END //

DELIMITER ;

②WHILE（ Judge before you execute ）

DELIMITER // 

CREATE PROCEDURE/FUNCTION  Stored procedure name / Stored function name ()

BEGIN
	# ① Initialize the loop condition 

	# ② The loop condition 
	[ Tagnames ]:WHILE  The loop condition  DO
		# ③ The loop body 
		# ④ Iteration conditions 
		[IF ...
			LEAVE  Tagnames ;
		END IF;]
		
	END WHILE;
	
END //

DELIMITER ;

③REPEAT（ Execute before judge , Unconditionally execute at least once ）

DELIMITER //

CREATE PROCEDURE/FUNCTION  Stored procedure name / Stored function name ()

BEGIN

	REPEAT
		 loop 
	UNTIL  --  Conditions for ending the cycle . Be careful ： This sentence has no `;` 
	END REPEAT;

END //

DELIMITER ;

（3） Jump statements ITERATELEAVE

①LEAVE Be similar to break

LEAVE  Tagnames 

②ITERATE Be similar to continue

Can only be used in LOOP/REPEAT/WHILE In loop statement

ITERATE  Tagnames 

4. trigger

event ： A user's action or triggering an action , Include INSERT, UPDATE, DELETE.

When executed INSERT, UPDATE, DELETE When an event is , The trigger will be automatically fired to perform the corresponding operation .

（1） Trigger creation

DELIMITER //

CREATE TRIGGER  Trigger Name 
{BEFORE|AFTER} {
   INSERT|UPDATE|DELETE} ON  Table name   -- ` Table name ` Objects monitored for triggers 
FOR EACH ROW

BEGIN
	 The block of statements executed by the trigger ;
	-- VALUE(NEW. Field name )
	-- VALUE(OLD. Field name )
END //

DELIMITER ;

• BEFORE In the event of Before Trigger
• AFTER In the event of after Trigger
• INSERT Express insert record Trigger when
• UPDATE Express Update record Trigger when
• DELETE Express Delete record Trigger when
• NEW Keyword is used to call the latest Insert The data of （ Use in The block of statements executed by the trigger Of VALUE In the sentence , Such as VALUE(NEW. Field name ) It can be used to view the newly inserted data value of this field .）
• OLD Keyword is used to call the most recent Delete The data of （ Use in The block of statements executed by the trigger Of VALUE In the sentence , Such as VALUE(OLD. Field name ) It can be used to view the recently deleted data value of this field .）

Verify that the trigger works
notes ： In the code above that creates the trigger BEGIN...END In the corresponding

BEGIN
The block of statements executed by the trigger

This statement block can be used to record the operation after triggering in Designated table in .
.
such , When an object monitored by a trigger triggers an operation , This Designated table The corresponding content will be recorded .
.
adopt SELECT * FROM Designated table ;, You can check whether the trigger is triggered .

END

（2） Check triggers

• Check the... Of the current database all The definition of trigger
  SHOW TRIGGERS
• View the current database Some The definition of trigger
  SHOW CREATE TRIGGER Trigger Name
• From the system library information_schema Of TRIGGER Query in table “salary_check_trigger” Trigger information
  SELECT * FROM information_schema.TRIGGERS;

（3） Delete trigger

DROP TRIGGER IF EXISTS  Trigger Name 

（4） Advantages and disadvantages of flip flops

advantage

• Ensure data integrity
• Help us record the operation log
• Before manipulating data , Check the validity of the data

shortcoming

• Poor readability （ Triggers are event driven , Not controlled by the application layer ）
• Change of relevant data , May cause trigger errors
• If a foreign key constraint is defined in the child table , And the foreign key specifies DML operation , At this time, modifying the parent table will also cause the corresponding operations of the child table . however , Corresponding based on sub table The trigger will not be activated .