Using stored procedures, timers, triggers to solve data analysis problems

author | python And data analysis

source |  Jay's IT The journey

Many do development 、 Small partners in database related work may often use MySQL Stored procedure 、 Timer 、 Trigger these advanced functions , But do data analysis or data processing , We also need to master these skills , To solve specific business problems . such as ： Make automated reports , If the data needs to be updated in real time every day （ Incremental crawler ）、 Calculate a business indicator regularly 、 Want to monitor the data increase in database tables in real time 、 Delete 、 Change the situation, etc .

Outline of the article

One 、 stored procedure

1、 What is a stored procedure , What's the usage? ？

• The process ： Put a number of SQL Statements are encapsulated , Name it

• stored procedure : We store this procedure in the database , It is a little similar to the functions used in programming , The difference is that the function has a return value , The procedure does not return a value , The same point is that the code is encapsulated and reusable , You can pass it on , Call to execute .

• benefits ：① Code encapsulation is reusable ② You can receive 、 Returns the parameter ③ Reduce network interaction 、 Improve efficiency

2、 How stored procedures are used

establish

create procedure  name ()
begin
  sql sentence ;
end

see

show procedure status;

call

call  name ();

Delete

drop procedure if exists  name ;

3、 Variables in stored procedures

Types and definitions of variables

stay SQL There are two kinds of variables in ：

• ① System variables ：@@

• ② Custom variable ：@

Stored procedures are programmable , It means that variables can be used 、 expression 、 Control structure , In the stored procedure , Declare variables with declare.

 Format ：declare  Variable name   Variable type  【default  The default value is 】

Variable operation and control structure

The assignment of a variable , There are two ways ：

• ① set Variable name = value

• ② set Variable name := value

if | else Control the structure syntax format

if   Conditions 1 then
  sql  sentence ;
else if  Conditions 2 then
  sql  sentence ;
else
  sql sentence ;
end if

Parameter passing in stored procedures

To make stored procedures more flexible , Parameters can be passed , There are three types of parameters ：

• ① in： Parameters as input , Pass in

• ② out： Parameter as output , It can be used as a return value

• ③ inout： Parameters can be passed in or entered

 Format : in|out|inout  Parameter name   Parameter type 

Use loops in stored procedures

while Circular format ：

while  Conditions  do
  sql  sentence ;
end while

Print 1 - 100 The sum of the

With input parameters n, seek 1-n The sum of the

Input parameters are required n, And output parameters total , seek 1-n The sum of the

requirement age Both input and output variables , Introduce an age , Increase 20

Two 、 Timer

1、 What is a timer , How to use it? ？

The so-called timer , Is to run the specified functions and code regularly ,MySQL The timer of is MySQL Events .

In the development process, we often encounter such a problem ： Every day or every month, it is necessary to implement one SQL Statement or update or delete data . I don't know MySQL When timer , Yes, it is Python Program code to operate the data table , then Python Program , Put it on the server to run the scheduled task . Now use the timer , It can be operated at the data level , Very convenient .

Grammatical structure

create event [if not exists]  Event name 
[definer = user]  Optional parameters . Of board ⾏ The event ⽤⼾, If you do not specify, the default is the current ⽤⼾
on schedule  Timing setting . Define event execution ⾏ The frequency of , You can specify a specific time or execute periodically 
[on completion [not] preserve ]  Optional parameters . The default is not, surface ⽰ After the time expires ⽴ Delete immediately ( Note that it is not inactive );on completion preserve  surface ⽰ After the time expires, it will continue to be retained 
[enable | disable | disable on slave]  Optional parameters . Default enable. Event activation 、 Do not activate 、 Do not activate from the service （ Events are created by the master service provider and assigned to the slave server , Execute only on the main service ）
[comment " notes "]  Optional parameters .
do  What happened   Define the sql sentence , If the statement has more ⾏ need ⽤ begin end  Cover up 

Specify a time to execute

at Clause ： The requirement here is timestamp Time format ,⼀ The general format is “ Point in time + interval Time unit ”. Indicates at what time node , for example ：current_timestamp + interval 2 minute

requirement ： Two minutes later event_test Table insertion ⼊⼀ statement " Event started "

Be careful ： Because the default parameter is on completion not preserve, The event will be automatically deleted after running

The cycle time is executed regularly ：

• every Clause ： The format is “ Numbers + Time unit ”, Represents the time period , for example ：1 hour / 2 minute / 3 second

• starts Clause ： Optional , keep pace with timestamp value , Indicates the time point when the event started , If not specified, it is the current time

• ends Clause ： Optional , keep pace with timesatamp value , Indicates the time to stop execution , without ends It means infinite execution

requirement ： New data table event_test, Insert it every minute ⼊⼀ Data , To 5 Minutes end

matters needing attention

1、 Events need to be activated , The event will be executed ,show events Before you can view it .⼀ The first is global parameter on ,⼀ The first is the opening of the event

SET GLOBAL event_scheduler = 1;
 Set the event status to  enable：
ALTER EVENT event_name ON COMPLETION PRESERVE ENABLE;  Turn on 
ALTER EVENT event_name ON COMPLETION PRESERVE DISABLE;  close 

2、 It's off navicat, The event will not close , Shut down the MySQL The server will be shut down
3、 When executing multiple statements , You may need to modify the end delimiter , such as ：delimiter $
4、 If the start time of the event has passed , Although the creation statement will not report an error , But events are not created and executed
5、 event ⾥⾯ Events cannot be nested , But events can be used in stored procedures
6、 Use... In events select、show Waiting for the return result statement is meaningless , But you can use select into、insert into Wait for the statement that stores the result
7、 Be careful not to repeat the event scheduling in a short period , Otherwise, there will be problems with the data . For example, execute every minute 100w Row data , There will be a problem with this , If you really need it, you can use row lock at this time 、 Watch lock
8、 event ⽆ Method to pass parameters , But you can use stored procedures with parameters in events

Timers can be combined with stored procedures

Now use the timer , You can operate at the data level , Do it regularly sql Statement or group sql sentence （ stored procedure ）, Set up scheduled tasks , It can be done by navicat —— Other —— event , View the definition of the current event , plan , Of course, you can also manually complete the above operations .

3、 ... and 、 trigger

1、 What is a trigger , The application scenario is ?

Triggers are a special kind of transaction , You can monitor data operations （ Change log of data table ）, Include insert | update | delete, And trigger related operations insert | update | delete, Use triggers , It can not only simplify the procedure , It can also increase the flexibility of the program .

Application scenarios ①： When adding or deleting data to a table , Synchronization operations need to be performed in related tables , such as ： When an order is generated , The inventory of the products purchased by the order is reduced accordingly .

Application scenarios ②： When the value of a column of data in the table is related to the data in other tables , such as ： A customer is in arrears , When generating an order , A trigger is designed to determine whether the accumulated debt of the user exceeds the maximum .

Application scenarios ③： When tracking a table , For example, when a new order is generated , It is necessary to inform relevant personnel to handle , At this time, you can add triggers in the order table to realize .

2、 How to use triggers

establish

Triggers only support row level triggering （ Each line is affected , All triggers execute , It is called row level trigger ）, Statement level triggering is not supported .

Create trigger  Trigger Name 
before/after  
insert/update/delete
on  Table name  for each row # Line level triggers 
Begin 
    trigger_state;
end

see

Show triggers;

Delete

Drop trigger  database . Trigger Name ;

requirement ： List of existing products goods, The order sheet orders, Next order , Commodities should be reduced accordingly ( Buy some goods , Just a few stocks ), The analysis is as follows ：

• Who to watch ：orders

• Watch the action ：insert

• Trigger time ：after

• Triggering event ：update

CREATE TABLE goods(gid INT,name VARCHAR(10),num SMALLINT);
CREATE TABLE ord(oid INT ,gid INT, buy_num SMALLINT)
INSERT INTO goods VALUES (1,'cat',20),(2,'dog',90),(3,'pig',26);

Check the product list

Create triggers and view

I found that writing triggers like this is not flexible

3、 Trigger references row variables

Use the alias old、new To refer to the changed record content in the trigger . Be careful ：

Reference line variables

requirement ： When deleting an order , The goods should be returned , Inventory should be restored （ Delete ）

requirement ： Quantity in the order table 3 Request to change to 2, And let the inventory of the commodity table also change （ Change ）

requirement ： If it's left now 26 only pig, But customers place orders to buy 27 only , Can we prevent , Could you please buy_num > num when , take buy_num Automatically change to num（ In depth understanding of before and after The difference between ）

The above introduces to you , How to analyze data in work , application MySQL Stored procedure 、 Timer 、 Trigger to automatically update data . Of course , use Python Or other programming languages , Personally, I think that at the data level , It's simpler 、 Efficient 、 Stable . It also depends on your current business scenario . I hope this article can provide you with a way to solve the problem .

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