mysql数据库中关于Cursor游标的使用方法_MySQL

mysql数据库中关于Cursor游标的使用方法

　DECLARE cursor_name CURSOR FOR SELECT_statement;

　　游标操作

　　OPEN 打开游标

　　OPEN cursor_name;

　　FETCH 获取游标当前指针的记录，并传给指定变量列表,注意变量数必须与MySQL游标返回的字段数一致,要获得多行数据，使用循环语句去执行FETCH

　　FETCH cursor_name INTO variable list;

　　CLOSE关闭游标

　　CLOSE cursor_name ;

　　注意:MySQL的游标是向前只读的,也就是说，你只能顺序地从开始往后读取结果集，不能从后往前，也不能直接跳到中间的记录

open 打开实例

mysql>
mysql> CREATE TABLE Employee(
    ->     id            int,
    ->     first_name    VARCHAR(15),
    ->     last_name     VARCHAR(15),
    ->     start_date    DATE,
    ->     end_date      DATE,
    ->     salary        FLOAT(8,2),
    ->     city          VARCHAR(10),
    ->     description   VARCHAR(15)
    -> );
Query OK, 0 rows affected (0.02 sec)

mysql>
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->              values (1,'Jason',    'Martin',  '19960725',  '20060725', 1234.56, 'Toronto',  'Programmer');
Query OK, 1 row affected (0.01 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(2,'Alison',   'Mathews',  '19760321', '19860221', 6661.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(3,'James',    'Smith',    '19781212', '19900315', 6544.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(4,'Celia',    'Rice',     '19821024', '19990421', 2344.78, 'Vancouver','Manager');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(5,'Robert',   'Black',    '19840115', '19980808', 2334.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(6,'Linda',    'Green',    '19870730', '19960104', 4322.78,'New York',  'Tester');
Query OK, 1 row affected (0.01 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(7,'David',    'Larry',    '19901231', '19980212', 7897.78,'New York',  'Manager');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date,   salary,  City,       Description)
    ->               values(8,'James',    'Cat',     '19960917',  '20020415', 1232.78,'Vancouver', 'Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> select * from Employee;
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| id   | first_name | last_name | start_date | end_date   | salary  | city      | description |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
|    1 | Jason      | Martin    | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto   | Programmer  |
|    2 | Alison     | Mathews   | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester      |
|    3 | James      | Smith     | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester      |
|    4 | Celia      | Rice      | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager     |
|    5 | Robert     | Black     | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester      |
|    6 | Linda      | Green     | 1987-07-30 | 1996-01-04 | 4322.78 | New York  | Tester      |
|    7 | David      | Larry     | 1990-12-31 | 1998-02-12 | 7897.78 | New York  | Manager     |
|    8 | James      | Cat       | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester      |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
8 rows in set (0.02 sec)

mysql>
mysql>
mysql>
mysql>
mysql> DELIMITER //www.3ppt.com
mysql> CREATE FUNCTION city_list() RETURNS VARCHAR(255)
    -> BEGIN
    ->
    ->         DECLARE finished INTEGER DEFAULT 0;
    ->         DECLARE city_name VARCHAR(50) DEFAULT "";
    ->         DECLARE list VARCHAR(255) DEFAULT "";
    ->         DECLARE city_cur CURSOR FOR SELECT city FROM employee;
    ->         DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1;
    ->
    ->         OPEN city_cur;
    ->
    ->         get_city: LOOP
    ->                 FETCH city_cur INTO city_name;
    ->                 IF finished THEN
    ->                         LEAVE get_city;
    ->                 END IF;
    ->                 SET list = CONCAT(list,", ",city_name);
    ->         END LOOP get_city;
    ->
    ->         CLOSE city_cur;
    ->
    ->         RETURN SUBSTR(list,3);
    -> END
    -> //
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;
mysql>
mysql> SELECT city_list() AS cities;
+------------------------------------------------------------------------------------+
| cities                                                                             |
+------------------------------------------------------------------------------------+
| Toronto, Vancouver, Vancouver, Vancouver, Vancouver, New York, New York, Vancouver |
+------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>
mysql> drop function city_list;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql>
mysql> drop table Employee;
Query OK, 0 rows affected (0.00 sec)

========
游标的Handler

mysql> DELIMITER //
mysql> CREATE FUNCTION city_list() RETURNS VARCHAR(255)
    -> BEGIN
    ->
    ->         DECLARE finished INTEGER DEFAULT 0;
    ->         DECLARE city_name VARCHAR(50) DEFAULT "";
    ->         DECLARE list VARCHAR(255) DEFAULT "";
    ->         DECLARE city_cur CURSOR FOR SELECT city FROM employee;
    ->         DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1;
    ->
    ->         OPEN city_cur;
    ->
    ->         get_city: LOOP
    ->                 FETCH city_cur INTO city_name;
    ->                 IF finished THEN
    ->                         LEAVE get_city;
    ->                 END IF;
    ->                 SET list = CONCAT(list,", ",city_name);
    ->         END LOOP get_city;
    ->
    ->         CLOSE city_cur;
    ->
    ->         RETURN SUBSTR(list,3);
    -> END
    -> //
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;
mysql>
mysql> SELECT city_list() AS cities;
+------------------------------------------------------------------------------------+
| cities                                                                             |
+------------------------------------------------------------------------------------+
| Toronto, Vancouver, Vancouver, Vancouver, Vancouver, New York, New York, Vancouver |
+------------------------------------------------------------------------------------+
1 row in set (0.02 sec)

mysql>
mysql> drop function city_list;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql>
mysql> drop table Employee;
Query OK, 0 rows affected (0.00 sec)
====

mysql 游标数据输出实例

mysql> delimiter $$
mysql> CREATE PROCEDURE myProc()
    ->     READS SQL DATA
    -> BEGIN
    ->      DECLARE l_last_row INT DEFAULT 0;
    ->      DECLARE l_dept_id  INT;
    ->      DECLARE c_dept CURSOR FOR
    ->           SELECT id
    ->             FROM employee;
    ->      /* handler to set l_last_row=1 if a cursor returns no more rows */
    ->      DECLARE continue handler for NOT FOUND SET l_last_row=1;
    ->
    ->      OPEN c_dept;
    ->      dept_cursor: LOOP
    ->           FETCH c_dept INTO l_dept_id;
    ->           IF (l_last_row=1) THEN
    ->                LEAVE dept_cursor;
    ->           END IF;
    ->           select l_dept_id;
    ->
    ->      END LOOP dept_cursor;
    ->      CLOSE c_dept;
    ->
    -> END$$
Query OK, 0 rows affected (0.01 sec)

mysql>
mysql> delimiter ;