JDBC call stored procedure, MySQL trigger

JDBC Calling stored procedure

• The load driver Class.forName

• Create database connection conn= DriverManager.getConnection

• Create processing block CallableStatement cs = conn.prepareCall

• Put in the parameters prepareCall.setString

• Execute stored procedures prepareCall.execute()

• Close the connection

Parameterless stored procedures

create procedure p1() begin 
	select * from t_users; 
end; 

--  Command line call  call p1();

JDBC Code call

Class.forName("com.mysql.cj.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql:///test?serverTimezone=UTC", "root", "123456"); 
CallableStatement cs = conn.prepareCall("{call p1()}"); 
cs.execute();
ResultSet rs = cs.getResultSet(); 
while(rs.next()){
     
	System.out.println(rs.getLong("id")+"\t"+rs.getString(2) +"\t"+rs.getDate("birth")); 
	}
rs.close();
cs.close();
conn.close();

Stored procedure definition with parameters

CREATE PROCEDURE add_pro(a INT,b INT,OUT ret INT) 
BEGINSET 
	ret=a+b; 
END
--  Calling method  
call add_pro(1,2,@cc);

select @cc;

Calling stored procedure

Class.forName("com.mysql.cj.jdbc.Driver"); 
Connection conn = DriverManager.getConnection("jdbc:mysql:///test? serverTimezone=UTC", "root", "123456"); 
CallableStatement cs = conn.prepareCall("{call add_pro(?,?,?)}"); 
cs.setInt(1, 123); 
cs.setInt(2, 300);
cs.registerOutParameter(3, Types.INTEGER); 
// Process the return value in the parameter   Register the return value type 
cs.execute(); 
int res=cs.getInt(3);
// Get the return value of the output parameter  
System.out.println(res); 
cs.close();
conn.close();

Special stored procedure parameters inout

CREATE PROCEDURE mul_pro(inout ret INT) 
BEGINSET 
	ret=ret*11; 
END

--  How to call the command line 
set @cc=5; 
call mul_pro(@cc); 
select @cc;

JDBC call

Class.forName("com.mysql.cj.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql:///test? serverTimezone=UTC", "root", "123456");
CallableStatement cs = conn.prepareCall("{call mul_pro(?)}");
cs.setInt(1, 9);
cs.registerOutParameter(1, Types.INTEGER); 
// Process the return value in the parameter   Register the return value type  
cs.execute(); 
int res=cs.getInt(1);
System.out.println(res); 
cs.close(); 
conn.close();

A stored procedure contains multiple query result sets

create procedure show1 (aid bigint) 
begin
	select * from t_users where id=aid;
    select * from t_roles where id=aid; 
end; 
--  Command line call 
call show1(2);

JDBC call

Class.forName("com.mysql.cj.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql:///test? serverTimezone=UTC", "root", "123456");
CallableStatement cs = conn.prepareCall("{call show1(?)}"); 
cs.setLong(1, 2L); 
cs.execute();
ResultSet rs = cs.getResultSet(); 
ResultSetMetaData rsmd = rs.getMetaData(); 
System.out.println("===================="); 
while (rs.next()) {
     
    for (int i = 1; i <= rsmd.getColumnCount(); i++) {
     
        System.out.print(rs.getObject(i) + "\t");
    } 
}
System.out.println(); // You need to customize the method to get data , Otherwise, the code to get the data part appears many times  
while (cs.getMoreResults()) {
     
    rs = cs.getResultSet(); 
    rsmd = rs.getMetaData();
    System.out.println("====================");
    while (rs.next()) {
    
        for (int i = 1; i <= rsmd.getColumnCount(); i++) {
    
            System.out.print(rs.getObject(i) + "\t"); 
        }
    }
    System.out.println(); 
}
rs.close(); 
cs.close();
conn.close();

MySQL trigger

A trigger is a database object , Is to insert in the data table 、 Delete 、 Operations such as update , And then it automatically triggers the pre

Some articles made up first SQL Execution of statements

characteristic

The operation that triggers the event and the... In the trigger SQL Statement is a transaction operation , It's atomic , Or all , Either not . such as ： bank transfer .

advantage

• SQL Triggers provide an alternative way to check data integrity

Checking constraints

create table t1(id int,name varchar(32),age int check(age between 18 and 65));

The database engine needs to use innodb,innodb Storage engine support transactions 、 Foreign keys and checking constraints . Check type constraint settings

In the table , No syntax errors , however DBMS It's not going to be checked

• SQL Triggers can catch errors in the business logic in the database layer .

• SQL Triggers provide another way to run scheduled tasks . By using SQL trigger , You don't have to wait to run a scheduled task , Because triggers are automatically called before or after changes are made to the data in the table

MySQL For disaster tolerance , Generally, the database needs to be backed up . The general schedule for backups is weekly 1 Full volume backup , Other time incremental backups . The backup time is generally selected to be performed at the time end with the least access , for example 0 Point to 1 Between points , You can schedule tasks or use triggers to automate backups

• SQL Triggers are very useful for auditing changes to data in a table .

shortcoming

• SQL Triggers can only provide extended validation , And cannot replace all validations . Some simple validation has to be done at the application layer . For example, you can use JavaScript Or the server-side uses the server-side scripting language to verify the user input of the client

• Calling and executing from a client application SQL Trigger not visible , So it's hard to figure out what's going on in the database layer .

• SQL Triggers can increase the overhead of the database server .

Basic grammar

CREATE TRIGGER trigger_name Trigger Name  trigger_time Triggering event  trigger_event Triggering event  
ON table_name The name of the table  FOR EACH ROW [trigger_order] 
trigger_body

• Trigger_time: Trigger execution time ： AFTER | BEFORE

• Trigger_event: Events triggered by triggers ： INSERT | UPDATE | DELETE

MySQL The triggers in can be divided into 3 Categories:

• FOR EACH ROW： Indicates that the trigger event will be triggered if the operation on any record satisfies the trigger event

Triggers can be divided into row level trigger and statement level trigger

• Table_name: Indicates the name of the trigger event operation table

• Trigger_body: To create a trigger SQL sentence

Typical applications

• BEFORE INSERT ： Before inserting data , Check whether the inserted data conforms to the business logic , If not, an error message will be returned

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• AFTER INSERT ： In the table A After creating a new account , Automatically write the creation success information to the table B in . Typical reconciliation processing

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auto_increment problem ：

insert Operation is only new surface , No, old surface . If the column auto_increment, be before when new.id The value is 0,after when new.id It is newly generated id value

• BEFORE UPDATE ： Before updating the data , Check whether the updated data conforms to the business logic , If not, an error message will be returned

CREATE TRIGGER validate_customer_level 
BEFORE UPDATE 
ON customers 
FOR EACH ROW
	IF OLD.level='VIP' THEN 
		SIGNAL SQLSTATE '45000' 
		SET MESSAGE_TEXT = 'VIP  Level customers cannot be downgraded to normal level customers ';
       END IF

update Table existing old It stores the data that needs to be replaced , And then there is new It is the data that needs to be newly added .old yes update Previous data ,new yes update Later data

• AFTER UPDATE ： After updating the data , Record the operation behavior in log in

CREATE TRIGGER log_sales_updates 
AFTER UPDATE 
ON sales
FOR EACH ROW 
	Insert into audit_log(sales_id, previous_amount, new_amount, updated_by, updated_on) VALUES (NEW.sales_id The new data ,OLD.sales_amount Old data , 
                                                                                                 NEW.sales_amount,(SELECT USER()), NOW())

• BEFORE DELETE ： Before deleting data , Check whether there is associated data , if there be , Stop deletion

  CREATE TRIGGER validate_related_records
  BEFORE DELETE ON customers 
  FOR EACH ROW 
  	IF OLD.customer_id in (select customer_id from sales) THEN
      	SIGNAL SQLSTATE '45000' 
      	SET MESSAGE_TEXT = ' This customer has an associated sales record , Can't delete .';
       END IF;
  

  The deletion operation can be divided into logical deletion and physical deletion , Basically, they are all logical deletion , The so-called logical deletion refers to adding a column in the table to identify whether the row data has been deleted ,deleted boolean default 0.delete Operation is only old surface , Where the data to be deleted is stored , No, new surface

• AFTER DELETE ： Delete table A After the message , Automatically delete table B Middle and table A Associated information .

  CREATE TRIGGER delete_related_info 
  AFTER DELETE 
  ON sales 
  FOR EACH ROW 
  	Delete from customers where customer_id=OLD.customer_id;
  

View memory

• SHOW TRIGGERS; See which triggers are in the database

• SHOW CREATE TRIGGER trigger_name;

NEW and OLD Application

MySQL It defines NEW and OLD Two temporary tables , Used to represent the table where the trigger is located , Which line of data triggers the trigger , To refer to the changed record content in the trigger , Whether the specific modification can take effect depends on whether the transaction is committed or rolled back

• stay INSERT Type trigger ,NEW It is used to intercept and save the information about （BEFORE） Or already （AFTER） New data inserted ;

• stay UPDATE Type trigger ,OLD Used to intercept and save the original data that will be or has been modified ,NEW Used to intercept and save new data that will or has been modified to .

• stay DELETE Type trigger ,OLD Used to intercept and save the original data that will be or has been deleted

Delete trigger

DELETE TRIGGER trigger_name;

Application restrictions

Triggers can take advantage in limited situations , Like statistics 、 Data table change log, etc . But there are also some flaws , For example, big data updates are triggered line by line , It reduces efficiency . And that is ,MyISAM The engine cannot guarantee atomicity . therefore , It depends on whether there are triggers in the application scenario .

The cursor

Cursors provide a flexible way to operate , Be able to locate each record in the result set , A data structure that operates on the data in the pointed record . Cursor let SQL This set oriented language has the ability of process oriented development in SQL in , A cursor is a temporary database object , Can point to the data row pointer stored in the database table . Here the cursor acts as a pointer , You can manipulate data rows by manipulating cursors .

advantage

• Allows the program to query statements select Each row in the returned row set performs the same or different operation , Instead of performing the same operation on the entire row set

• Provides the ability to delete and update rows in a table based on cursor position

• Cursors are actually a collection oriented database management system RDBMS And line oriented programming , Make these two processing methods communicate through cursors .

shortcoming

Cursors cause some performance problems , For example, in the process of using cursors , Data rows will be locked , In this way, when there is a large amount of business concurrency , It will not only affect the efficiency between businesses , It also consumes system resources , Cause insufficient memory , This is because cursors are processed in memory .

principle

Cursor is to extract the corresponding data set according to the specified requirements , Then the data is processed one by one . The order of using cursors ： Reputation cursor 、 Open cursor 、 Reading data 、 Close cursor 、 Delete cursor .

Trigger limit

mysql Trigger coverage criteria SQL All functions defined in , however , There are also some limitations to using them in applications ：

• Use in SHOW,LOAD DATA,LOAD TABLE,BACKUP DATABASE,RESTORE,FLUSH and RETURN Above statement

• Use implicit or explicit commit or rollback statements , Such as COMMIT,ROLLBACK,START TRANSACTION,LOCK/UNLOCK TABLES,ALTER,CREATE,DROP,RENAME etc.

• Use the prepare statement , Such as PREPARE,EXECUTE etc.

• Usage dynamics SQL sentence

Attention problem

from MySQL 5.7.2+ Version start , Multiple triggers can be defined for the same trigger event and action time . When used or not used INSERT,DELETE or UPDATE Statement changes the statement of data in the table , Triggers associated with tables are not called . for example ,truncate Statement to delete all data from a table , But do not call the trigger associated with the table . however , Some statements use the background INSERT sentence , Such as REPLACE Sentence or LOAD DATA sentence . If you use these statements , The corresponding trigger associated with the table is called . So you must use a unique name for each trigger associated with the table . You can define the same trigger name for different tables , This is a good way .