MySQL cursor operation guide

MySQL cursor operation guide
This article provides a detailed analysis of the usage of MySQL cursors. For more information, see

Test Table level

The Code is as follows:

create table test.level (name varchar(20));

Insert some data;

Initialization

The Code is as follows:

drop procedure if exists useCursor //

The create code for creating a stored procedure is as follows:

CREATE PROCEDURE useCursor() BEGIN

The declare code for defining local variables is as follows:

declare tmpName varchar(20) default '' ;  declare allName varchar(255) default '' ;  declare cur1 CURSOR FOR SELECT name FROM test.level ; 

Capture when a MySQL cursor is abnormal

 

And set the loop to jump out of the loop with the variable tmpname null.

The Code is as follows:

declare CONTINUE HANDLER FOR SQLSTATE '02000' SET tmpname = null;

　　

The code for opening a cursor is as follows:

OPEN cur1;

　　

The cursor goes down with the following code:

FETCH cur1 INTO tmpName;

　　

Loop body, which obviously adds the names queried by the MySQL cursor and uses them; Code to separate the numbers is as follows:

WHILE ( tmpname is not null) DO set tmpName = CONCAT(tmpName ,";") ; set allName = CONCAT(allName ,tmpName) ;

　　

The cursor goes down with the following code:

FETCH cur1 INTO tmpName;

　　

End loop body: the code is as follows:

END WHILE;

　　

The code for disabling a cursor is as follows:

CLOSE cur1;

　　

The data selection code is as follows:

select allName ;

　　

The code for ending the stored procedure is as follows:

END;//

　　

Call the stored procedure: the code is as follows:

call useCursor()//

 
Loop cursor: the code is as follows:

DELIMITER $$  DROP PROCEDURE IF EXITS cursor_example$$  CREATE PROCEDURE cursor_example()       READS SQL DATA  BEGIN       DECLARE l_employee_id INT;       DECLARE l_salary NUMERIC(8,2);       DECLARE l_department_id INT;       DECLARE done INT DEFAULT 0;       DECLARE cur1 CURSOR FOR SELECT employee_id, salary, department_id FROM employees;       DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;       OPEN cur1;       emp_loop: LOOP           FETCH cur1 INTO l_employee_id, l_salary, l_department_id;           IF done=1 THEN               LEAVE emp_loop;           END IF;       END LOOP emp_loop;       CLOSE cur1;  END$$  DELIMITER ; 

　　

Repeat loop cursor: the code is as follows:

/* Creation process */DELIMITER // drop procedure if exists test // create procedure test () begin declare done int default 0; DECLARE a VARCHAR (200) DEFAULT ''; DECLARE c VARCHAR (200) DEFAULT ''; DECLARE mycursor cursor for select fusername FROM uchome_friend; declare continue handler for not found set done = 1; OPEN mycursor; repeat fetch mycursor INTO; if not done then set c = CONCAT (c, a);/* string addition */end if; UNTIL done end repeat; CLOSE mycursor; SELECT c; END // DELIMITER;

　　

The Code is as follows:

/* Creation process */DELIMITER // drop procedure if exists test // create procedure test () begin declare done int default 0; DECLARE a VARCHAR (200) DEFAULT ''; DECLARE c VARCHAR (200) DEFAULT ''; DECLARE mycursor cursor for select fusername FROM uchome_friend; declare continue handler for not found set done = 1; OPEN mycursor; repeat fetch mycursor INTO; if not done then set c = CONCAT (c, a);/* string addition */end if; UNTIL done end repeat; CLOSE mycursor; SELECT c; END // DELIMITER;