循环遍历结果行并将列数据存储到存储过程变量mysql中 [英] looping through result rows and storing column data into stored procedure variables mysql

问题描述

我正在尝试在mysql中学习存储过程.我知道下面的示例不需要SP，但这只是出于我的学习目的-只是为了了解如何循环遍历行以及在行内选择特定的列数据.

I m trying to learn stored procedure in mysql. I know the below example does not need SP, but this is ONLY for my learning purpose - just to understand how to loop through rows, and pick specific column data inside the row.

假设该表上的SELECT从我的表中返回5条具有以下结构的记录-

Assume that a SELECT on the table returns 5 records from my table with following structure -

表名称:t1 列:c1，c2，c3

table name: t1 columns: c1,c2,c3

我想遍历5行中的每行，对于每行，我想将列单元格数据存储到SP变量varc1，varc2，varc3中，这样varc1 = c1，varc2 = c2，varc3 = c3.我将在循环内使用这些varc1，varc2，varc3进行进一步的计算.

i would like to loop through each of the 5 rows, and for each row, i would like to store the column cell data into SP variables varc1,varc2,varc3, so that varc1 = c1, varc2 = c2, varc3 = c3. i would be using these varc1,varc2,varc3 for further computation while within the loop.

我假设需要一个存储过程，但是我没有采用这种方法进行行迭代，然后从循环中考虑的行中的每一列中选择数据.

i am assuming that a stored procedure is required, but i am not getting the approach in doing the row iteration and then picking data from each column in the row under consideration in the loop.

是mysql/存储过程的新手. 谢谢！

quite new to mysql/ stored procedure. thank you!

推荐答案

您似乎想知道的是，对于大多数问题而言，这是一种效率特别低下的解决方案.但是，由于您是专门要求它的，而且(偶尔)是解决问题的唯一方法(或者您个人有时间弄清楚如何解决问题的唯一方法).这是您可能会做的事情:

What your asking for, as you seem to know, is a particularly inefficient solution to most problems. However, since you specifically asked for it, and since (very occasionally) it's the only way to solve a problem (or the only way you personally have time to figure out how to solve it). Here's how you might do what you ask:

创建您的t1表，例如:

Create your t1 table eg:

CREATE TABLE t1(id INT PRIMARY KEY NOT NULL AUTO_INCREMENT, C1 INT, C2 INT, C3 INT);

执行您描述的SELECT，例如:

Carry out your SELECT that you describe eg:

INSERT INTO  t1 SELECT NULL,c1,c2,c3 FROM the_table; 

现在这是您的按行行"ReeBAR"低效率存储过程:

Now here's your Row-By-Agonising-Row "ReeBAR" low efficiency stored procedure:

为过程准备空间并设置定界符:

Prepare space for your procedure and set the delimiter:

DROP PROCEDURE IF EXISTS ReeBAR;
DELIMITER ;;

编写您的程序:

CREATE PROCEDURE ReeBAR()
BEGIN
DECLARE n INT DEFAULT 0;
DECLARE i INT DEFAULT 0;
DECLARE varc1 INT DEFAULT 0;
DECLARE varc2 INT DEFAULT 0;
DECLARE varc3 INT DEFAULT 0;
SELECT COUNT(*) into n FROM t1;
set i=1;
WHILE i<=n DO 
  SELECT c1 FROM t1 WHERE id=i INTO varc1; 
  SELECT c2 FROM t1 WHERE id=i INTO varc2;
  SELECT c3 FROM t1 WHERE id=i INTO varc3;
  --queries which couldnt be made into set based queries go here---
  SET i = i + 1;
END WHILE;
End;

或者，如果您的id列不连续，则可以使用以下游标形式.

Alternatively if your id column in not sequential you can use the follwoing cursor form.

CREATE PROCEDURE ReeBAR()
BEGIN
  DECLARE cursor_ID INT;
  DECLARE cursor_VAL VARCHAR;
  DECLARE done INT DEFAULT FALSE;
  DECLARE cursor_i CURSOR FOR SELECT c1,c2,c3 FROM t1;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
  DECLARE varc1 INT DEFAULT 0;
  DECLARE varc2 INT DEFAULT 0;
  DECLARE varc3 INT DEFAULT 0;
  OPEN cursor_i;
  read_loop: LOOP
    FETCH cursor_i INTO varc1, varc2, varc3;
    IF done THEN
      LEAVE read_loop;
    END IF;
    --queries which couldnt be made into set based queries go here---
  END LOOP;
  CLOSE cursor_i;
END;

别忘了结束"您使用的过程并重置定界符

Don't forget to "end" the procedure you use and reset the delimiter

;;
DELIMITER ;

最后运行您的ReBAR程序

Finally to run your ReBAR procedure

CALL ReeBAR();

(未经测试的代码)

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