当前位置:网站首页>Use the fetch statement to obtain the repetition of the last row of cursor data
Use the fetch statement to obtain the repetition of the last row of cursor data
2022-07-07 10:22:00 【qq_ forty-two million one hundred and twenty thousand eight hun】
- Problem description :《MySQL Will know 》 Medium P179 After the execution of the stored procedure, a row is repeatedly inserted in the new table .
- stored procedure processorders( To calculate the orders The total amount of each order in the table and deposit in a new table )
# Create a stored procedure to calculate the total amount of each order and store it in a new table
DELIMITER //
CREATE PROCEDURE processorders()
BEGIN
# Declare local variables
DECLARE done BOOLEAN DEFAULT 0;
DECLARE o INT;
DECLARE t DECIMAL(8,2);
# declare cursor
DECLARE ordernumbers CURSOR
FOR
SELECT order_num FROM orders;
# Declare exception handling , When sql Status as 02000 when , take done Set to 1
DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1;
# Create a new table to store the results
CREATE TABLE IF NOT EXISTS ordertotals
(order_num INT,
total DECIMAL(8,2)
);
# Open cursor
OPEN ordernumbers;
# Insert all rows in a loop
REPEAT
# Get the order number , When the intra row pointer points to the next row of the last row, executing this statement will make SQLSTATE='02000'
# Cause the execution of the upper handle processing to make done = 1
FETCH ordernumbers INTO o;
# Calculate the total amount with tax , The result will be returned to the parameter t, The stored procedure is at the bottom
CALL ordertotal(o,1,t);
# Insert the order number and total amount into the table
INSERT INTO ordertotals(order_num,total)
VALUES(o,t);
UNTIL done # The end cycle condition is done For the wrong 0
END REPEAT;
# Close cursor
CLOSE ordernumbers;
END//
# Execute query statement
CALL processorders()//
- The result
- Problem analysis : When the pointer in the cursor points to the next row of the last row , Re execution
FETCH ordernumbers INTO o;
When this statement , To take the current line and move the pointer down one line , Because the position pointed by the pointer is illegal , So there is a row error , Cause the upper handle processing to trigger , bring done = 1, And then o No new data is inserted , Or the old data of the last round ( That is, the order number in the last line ), Therefore, the last line is repeatedly inserted twice .
resolvent : stay FETCH Judge immediately after the statement is executed done Is it modified to 1, If it is modified to 1, Then the following insert code will not be executed . The stored procedure code above is modified to
DELIMITER //
CREATE PROCEDURE processorders()
BEGIN
# Declare local variables
DECLARE done BOOLEAN DEFAULT 0;
DECLARE o INT;
DECLARE t DECIMAL(8,2);
# declare cursor
DECLARE ordernumbers CURSOR
FOR
SELECT order_num FROM orders;
# Declare exception handling , When sql Status as 02000 when , take done Set to 1
DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1;
# Create a new table to store the results
CREATE TABLE IF NOT EXISTS ordertotals
(order_num INT,
total DECIMAL(8,2)
);
# Open cursor
OPEN ordernumbers;
# Insert all rows in a loop
REPEAT
# Get the order number , When the intra row pointer points to the next row of the last row, executing this statement will make SQLSTATE='02000'
# Cause the execution of the upper handle processing to make done = 1
FETCH ordernumbers INTO o;
IF !done THEN # The key position of the correction
# Calculate the total amount with tax , The result will be returned to the parameter t, The stored procedure is at the bottom
CALL ordertotal(o,1,t);
# Insert the order number and total amount into the table
INSERT INTO ordertotals(order_num,total)
VALUES(o,t);
END IF;
UNTIL done
END REPEAT;
# Close cursor
CLOSE ordernumbers;
END//
Query again ordertotals The result of the table is
Reference material :
边栏推荐
- How to cancel automatic saving of changes in sqlyog database
- ISP、IAP、ICP、JTAG、SWD的编程特点
- Bean operation domain and life cycle
- LeetCode 练习——113. 路径总和 II
- 大整数类实现阶乘
- The new activity of "the arrival of twelve constellations and goddesses" was launched
- Can I open a stock trading account online? Is it safe
- mysql插入数据创建触发器填充uuid字段值
- Horizontal split of database
- 单片机(MCU)最强科普(万字总结,值得收藏)
猜你喜欢
随机推荐
STM32 Basics - memory mapping
Fiddler simulates the interface test
高数_第1章空间解析几何与向量代数_向量的数量积
China's first electronic audio category "Yamano electronic audio" digital collection is on sale!
JMeter about setting thread group and time
fiddler-AutoResponder
Word自动生成目录的方法
【acwing】786. Number k
Postman tutorial - scripting
Advanced function learning in ES6
嵌入式背景知识-芯片
ISP、IAP、ICP、JTAG、SWD的编程特点
The method of word automatically generating directory
串口通讯继电器-modbus通信上位机调试软件工具项目开发案例
UnityWebRequest基础使用之下载文本、图片、AB包
Embedded background - chip
IPv4 socket address structure
2022.7.3DAY595
嵌入式工程师如何提高工作效率
Programming features of ISP, IAP, ICP, JTAG and SWD