In depth MySQL transactions, stored procedures and triggers

stored procedure

One or more stored for future use mysql Collection of statements . Vaguely, it can be regarded as a batch file .

It's a function . Yes , Equivalent to C Functions in language 、c++/java The method in . You can call , Improve SQL Operational efficiency .

In general , Users with normal permissions only have the permission to use stored procedures , Without permission to write , Yes , Stored procedures are also convenient for users to query （ We will talk about “ Create intelligent scenarios ”）, It is also user oriented .

Execute stored procedures ：mysql The execution of a stored procedure is called , therefore mysql The statement to execute the stored procedure is CALL.CALL Receive the name of the stored procedure and any parameters that need to be passed to it . The following is a stored procedure for a program ：

CALL productpricing(@pricelow, @pricehigh, @priceaverage);

among , Return the lowest （pricelow）、 The highest （pricehigh）、 And the average price （priceaverage）.

Create stored procedure ： Direct orders ：

create procedure pro()
begin
    select avg(prod_price) as priceaverage

    from products;
end;

This stored procedure is called Pro, use create procedure pro() Definition . If the stored procedure receives parameters , They will be in （） To list out .

among ,begin and end Statement is used to define the body of a stored procedure , The process body is just a select sentence .

If you're using mysql Command line utility , Attention should be paid to ：mysql Command line utilities and mysql The default is the same , take “;” Treat as separator , They will not eventually be called components of stored procedures , This will make SQL sentence in wrong . terms of settlement ： Add a line at the beginning ：delimiter // —— Tell the command line utility to use // As a new statement end separator , And then end Situated ; Change it to //, Add another line at the end ：delimiter ;—— To reply to the original statement separator

then , How to use ？

CALL pro();

Execute the newly created stored procedure ;（ Generally, variables are passed in brackets here ）

Why? Pro There's going to be （）？—— A stored procedure is actually a function .

Delete stored procedure

drop procedure pro;

Please note that , Not using the latter （）, Just give the stored procedure name .

but, If the specified procedure does not exist , Then the above statement will be wrong . We can use ：drop procedure if exists; （ About if exists, I'll see you later , It is widely used in the establishment of intelligent stored procedures ）

Using parameter ： commonly , Stored procedures do not display results , Instead, return the result to the variable you specified .

Variable ： A specific location in memory , Used to temporarily store data .

Here are Pro Modified version of ：

create procedure pro(
    out p1 decimal(8,2),
    out p2 decimal(8,2),
    out p3 decimal(8,2)
)

begin
    select min(prod_price)
    into p1
    from products;
    select max(prod_price)
    into p2
    from products;
    select avg(prod_price)
    into p3
    from products;
end;

This process receives three parameters ：p1 The lowest price for storage products ,p2 The highest price of storage products ,p3 Average storage price of products . Each parameter must have a specified type . keyword out Point out the corresponding parameters to pass a value from the stored procedure （ Back to the caller ）.

mysql Support IN（ Pass to stored procedure ）、out（ From stored procedure ）、 and INOUT（ Pass in and out of stored procedures ） Parameters of type

IN Input parameters : The value representing the parameter must be specified when the stored procedure is called , Modifying the value of this parameter in a stored procedure cannot be returned , As the default value

OUT Output parameters : This value can be changed within the stored procedure , And can return

INOUT Input/output parameter : When called, specifies , And can be changed and returned

Ⅰ.IN Parameter example

establish :

mysql > DELIMITER // 

mysql > CREATE PROCEDURE demo_in_parameter(IN p_in int) 

-> BEGIN  

-> SELECT p_in;  

-> SET p_in=2;  

-> SELECT p_in;  

-> END;  

-> //  

mysql > DELIMITER ; 

Execution results :

mysql > SET @p_in=1; 

mysql > CALL demo_in_parameter(@p_in); 

+------+ 

| p_in | 

+------+ 

|   1  |  

+------+ 

 +------+ 

| p_in | 

+------+ 

|   2  |  

+------+ 

mysql> SELECT @p_in; 

+-------+ 

| @p_in | 

+-------+ 

|  1    | 

+-------+ 

As can be seen above ,pin Although it is modified in the stored procedure , But it doesn't affect @pid Value

Ⅱ.OUT Parameter example

establish :

mysql > DELIMITER // 

mysql > CREATE PROCEDURE demo_out_parameter(OUT p_out int) 

-> BEGIN 

-> SELECT p_out; 

-> SET p_out=2; 

-> SELECT p_out; 

-> END; 

-> //  

mysql > DELIMITER ; 

Execution results :

mysql > SET @p_out=1; 

mysql > CALL sp_demo_out_parameter(@p_out); 

+-------+ 

| p_out |  

+-------+ 

| NULL  |  

+-------+ 

 +-------+ 

| p_out | 

+-------+ 

|   2   |  

+-------+ 

 mysql> SELECT @p_out; 

+-------+ 

| p_out | 

+-------+ 

|   2   | 

+-------+ 

Ⅲ.INOUT Parameter example 

 establish :

mysql > DELIMITER //  

mysql > CREATE PROCEDURE demo_inout_parameter(INOUT p_inout int)  

-> BEGIN 

-> SELECT p_inout; 

-> SET p_inout=2; 

-> SELECT p_inout;  

-> END; 

-> //  

mysql > DELIMITER ; 

Execution results :

mysql > SET @p_inout=1; 

mysql > CALL demo_inout_parameter(@p_inout) ; 

+---------+  

| p_inout | 

+---------+  

|    1    | 

+---------+  

 +---------+  

| p_inout |  

+---------+  

|    2    | 

+---------+  

mysql > SELECT @p_inout; 

+----------+  

| @p_inout |  

+----------+  

|    2     | 

+----------+ 

As I saw before , Stored procedures are a series select sentence , Used to retrieve values , adopt INTO Save keyword to corresponding variable .

mysql There are global variables and local variables ：

1. local variable ： With keywords DECLARE Statement , Followed by variable name and variable type , Such as ：declare a int

 You can also use keywords DEFAULT Specify default values for variables , Such as ：declare a int default 10

2. Global variables ：mysql The session variables in are global variables , Session variables are valid throughout the process , It takes characters “@” start , Such as ：

delimiter //
create procedure p2()

begin
set @t=1;

begin
set @t=2;
select @t;
end;

select @t;

end;

delimiter //

To call the modified stored procedure , Must specify 3 Variable names , namely ：

CALL productpricing(@pricelow, @pricehigh, @priceaverage);

all mysql All variables must be in @ Start .

For reasons of length , Please pay attention to my other blog posts for specific matters , I won't elaborate here ...

Of course , The most important of these is , It supports various conditional statements , Such as ：IF sentence （ First judgement IF Whether the post condition is true , When true, execute the following THEN The following sentence , If false, continue to judge ）、CASE sentence （ First of all, from the WHEN After value Search for and CASE After value Equal value , If found, execute the contents of the branch ）、WHILE Loop statement （ First judgement condition Is the condition true , When true, execute the loop body ）、LOOP Loop statement （LOOP Allow some giant specific repetition , Implement a simple loop construct , Exit the cycle with LEAVE sentence ）、REPEAT Loop statement （ First execute the loop body , And then determine condition Is the condition true , When true, exit the loop ）

Example ：

1.LOOP

delimiter //
create procedure edxloop(out sum int)

begin
declare i int default 1;
declare s int default 0;
loop_lable:loop
set s=s+i;

set i=i+1;

if i>100 then

leave loop_lable;

end if;

end loop;

set sum=s;

end

delimiter //

call exloop(@s);

.................................

select @s;

Storage function ： The same routine as stored procedures , It's just ,create hinder procedure Turned into function. as follows ：

delimiter //

create function name_of_student(std_id int)

return varchar(15)

begin

return(select name from syidentinfo where std=std_id);

end

delimiter //

Two return Be short of one cannot , The first one is the type of the parameter , The second is the query results .

Call stored procedures and stored functions ：1. Calling stored procedure ： As mentioned earlier call,yes, Through the previous example, it must be unnecessary to say this at all ,OK,To proceed to the next item!

2. Calling the storage function ： direct select Function name （ Parameters ）; that will do

View the definitions of stored procedures and stored functions ：SHOW CREATE sentence

show create procedure/function name ;

Check the status of stored functions and stored procedures ： Such as ：show procedure status like 'filminstock'; ( Check out the process filminstock Information about )

Delete stored procedures and stored functions ：drop procedure/function [IF EXISTS] name ;

trigger

above “ Storage function ” Medium “DELIMITER //” The same as when creating triggers , So here is the trigger .

Let's talk about triggers first , In fact, I have learned java Everyone knows that one of them is “ I've been fascinated for a long time ” Things that are , It's called “ The monitor ”, Common as ： Mouse monitor , It can realize mouse operation ; Time monitor 、 Color monitor, etc ...

The trigger in the database is similar to this principle ： In the implementation of a “ Operations to be monitored ” Set trigger , Trigger is raised during execution , Let the system complete the established procedures .

Create trigger ：

CREATE TRIGGER Trigger Name BEFORE|AFTER Triggering event ON Table name FOR EACH ROW Execute statement

before and after： Specify the time when the trigger executes （ Before or after the trigger time ）;

for each row： Indicates that the trigger event will be triggered if the operation on any record satisfies the trigger event ;

Execute statement ： Refers to the program executed after the trigger is triggered

for example ： Create a file called timelog Table of

create table timelog(
    id int primary key auto_increment,
    savetime varchar(50) not null
);

Create a save_time The trigger of

delimiter //

create trigger save_time before insert

on studentinfo for each row

insert into timelog(savetime) values(now());

delimiter //

insert That sentence is “now（）”, So let's return a message ： Time to run this operation ！

This is the function of trigger .

Above is a single event , What if there are multiple events ？

Created above timelog On the basis of , Create another one named timeinfo Data sheet for

create table timeinfo(
    id int primary key,
    info varchar(50) not null
);

And then create one by DELETE Trigger of multiple statements triggered , as follows ：

delimiter //

create trigger delete_time_info after delete

on studentinfo for each row

begin

insert into timelog(savetime) values(now());

insert into timeinfo(info) values(now());

end

delimiter //

The code that performs the delete operation （ The command that triggers the trigger ） by ：

DELETE FROM studentinfo where name='Chirs';

then , use select Statement to view timelog Data sheets and timeinfo Data sheet , You can see the returned result .

Check triggers ： use SHOW TRIGGERS; Check the basic information of trigger ;

Delete trigger ： use DROP TRIGGER Trigger Name ;

Take a look at the complete example of a trigger ：

One 、 establish MySQL Instance data table ：

stay mysql The default test test Under database , Create two tables ta And tb：

/*Table structure for table `t_a` */

DROP TABLE IF EXISTS `t_a`;

CREATE TABLE `t_a` (
    `id` smallint(1) unsigned NOT NULL AUTO_INCREMENT,
    `username` varchar(20) DEFAULT NULL,
    `groupid` mediumint(8) unsigned NOT NULL DEFAULT '0',
    PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=16 DEFAULT CHARSET=latin1;

 

/*Data for the table `t_a` */

LOCK TABLES `t_a` WRITE;
UNLOCK TABLES;

 

/*Table structure for table `t_b` */
DROP TABLE IF EXISTS `t_b`;

CREATE TABLE `t_b` (
    `id` smallint(1) unsigned NOT NULL AUTO_INCREMENT,
    `username` varchar(20) DEFAULT NULL,
    `groupid` mediumint(8) unsigned NOT NULL DEFAULT '0',
    PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=57 DEFAULT CHARSET=latin1;

 

/*Data for the table `t_b` */
LOCK TABLES `t_b` WRITE;

UNLOCK TABLES;

stay ta Create one on the table CUD（ increase 、 Change 、 Delete ）3 Trigger , take ta Table data and t_b Synchronous implementation CUD, Note that each table has only one corresponding trigger for the same event , Why only one trigger , No explanation , see MYSQL Help documentation for instructions .

MySQL Business

First say ,mysql Variables are really a magical thing , It can not only be simulated by stored procedures and stored functions c/c++/java Function of （ Method ）,mysql The view of variables is also added in (select @ Variable ).

What does this have to do with what we are going to say ？ No, .

stay mysql in , A transaction consists of one or more separate units SQL Sentence composition , In this unit , Every mysql Statements are interdependent .

Let's talk about it first , What are the applications of transaction data ？

online shopping , Users log on to the website , Browse information , Put your favorite items in the shopping cart , Then pay online , When the user finishes paying , Inform the merchant to deliver the goods , Be careful , At this time, the merchant did not receive the payment , When the user receives the goods , Click confirm receipt , The merchant received the payment , The whole deal is done . Imagine when users choose products , Choose to cancel the order during shipment , This is business did not get payment will cancel operation , If transactions are not used , After the user cancels the operation , Merchants still deliver goods to users , It will cause some unhappiness . Therefore, in the whole transaction process , Transaction rollback operation must be taken .

Simply speaking , Transaction is to add a “ insurance ”.

Tips ：mysql Transactions are only for InnoDB and BDB Type table , When we create tables, the default is MyISAM Type table .

Atomicity ： That is, the integrity and indivisibility of the transaction , All transactions go forward and backward . Or say , The execution of atoms is a whole process of all occurrences or all failures . In an atomic operation , If any statement of the transaction fails , The statements executed earlier will be returned , I. ensure that the integrity of the data is not destroyed .

Uniformity ： be based on mysql Journal processing mechanism , Record all changes in the database , Provide trace records for transaction recovery . Such as ： user A To the user B Transfer accounts 5000 element , user B But I found that my account only increased 3000 element , Is it very sad ...

persistence ： Committed transactions even mysql The system crashed and still kept running . When a transaction is completed , When the database log has been updated , Persistence can play its unique role . and , stay mysql in , If the system crashes or the data storage medium is damaged , By using logs , The system can recover the last successful update before restart .

Isolation

By default ,InnoDB Tables last the longest .

Creation of affairs

The process is a bit cumbersome ： Initialize transaction 、 Create transaction 、 application select Statement to query whether the data is entered 、 Commit transaction .

1. Create a table ：create table table_name(field-defintions) type=INNODB/BDB;

table_name Is the name of the table ,field-defintions It is an in table field 

 If users want to support transaction processing for existing tables , Applicable ALTER Command to specify ：alter table table_name type=INNODB/BDB;

2. Initialize transaction ：start transaction;

3. Create transaction ： After successful initialization , Insert data into table , Such as ：

insert into connection(email,cellphone,qq,sid) values('[email protected]',123456789,8975645,3);

3. see ： Such as ：select * from connection where sid=3;

4. Commit transaction ： Before the user commits the transaction , When other users connect mysql Server time , use select The query will not show the added transactions .

 Commit transaction command ：COMMIT

Cancellation of transaction （ Transaction rollback ）：ROLLBACK command . If a rollback operation is performed , Then enter start transaction All after the command SQL Statement will execute rollback operation .

If the user commits the transaction , No transaction committed , The transaction defaults to automatic rollback .

How to use transaction rollback ？ We need to set up a savepoint Variable , I call it ： Rollback label . When rollback is needed , just rollback Just go to the place of this label . Such as ：

savepoint test;

...

...

rollback to savepoint test;

Transactions do not support nested use , When the user reopens a transaction before ending the first transaction , The previous transaction will be automatically committed , Again mysql Many commands in the command will hide the execution COMMIT command ;

MySQL Behavior

1. About mysql Automatic submission ： If the user does not want to control MySQL Auto submit parameters , You can change the submission mode , Such as ： Use “SET AUTOCOMMIT=0;” The command turns off auto submit parameters , thereafter , Only when the user enters COMMIT after ,mysql In order to submit the data in the data table to the database .

We can check （select）“@@AUTOCOMMIT” Variable to view the current auto submit status .

mysql Isolated level

1. be based on ANSI/ISO SQL standard ,MySQL Provide 4 Medium isolated level , Namely ：SERIALIZABLE（ serialize ）、REPEATABLE READ（ Can be reread ）、READ COMMITTED（ Submit and read ）、READ UNCOMMITTED（ Uncommitted read ）.

2. Modify the orphan level of the transaction ：mysql The default isolation level is “ Can be reread ”, The user can use the command ：set global transaction isolation level Isolated level name ; To modify the level ; can use select Command to get the value of the orphan level variable of the current transaction ：select @@tx_isolation;

3. If ordinary users want to modify the isolation level of transactions , You have to get SUPER jurisdiction .

Table locking ？——MyISAM Middle simulation InnoDB/BDB Business stuff

abbreviation , Pseudo transaction .

purpose ： Avoid interference during user operation of the database .

The basic steps to set table locking instead of transactions are as follows ：

（1） Add a lock to the specified table ：LOCK TABLES tablename locktype,......

 among ,lock_type Refers to the type of lock , Divided into two ： Read （READ） And in writing （WRITE）

 One . Read ： Lock the user to operate in other ways （ Such as ： Delete , Insert , to update ）

     With studentinfo Table as an example ：lock table studentinfo read;

     After performing this step , Then insert data into the table , Will report a mistake ！

 Two . In writing ： Set that users can modify the data in the table , However, users in other sessions except themselves cannot perform any read operations .

    lock table studentinfo write;

     thereafter , Conduct select * from studentinfo when , The results will not be displayed .