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mysql - 使用游标循环存储过程并将返回值存储到变量中

问题描述

我的查询应该在遍历表 table_a 的游标时检查 table_b 中是否存在值。如果 table_b 中存在值，则将值返回到变量 @yyy。
当我运行这个存储过程时，我应该得到一个返回 col2、col3、col1 的值。但它只返回 col2、col3。
在这个查询中，当我使用它时，into @yyy我觉得它没有按需要的方式工作。不确定是什么问题。你能帮忙吗？
只需通过删除into @yyy我可以获得正确的结果，但我需要对变量进行更多更改，@yyy这就是我需要将结果存储到其中的原因。

Delimiter $$
DROP PROCEDURE IF EXISTS sp_test3;
CREATE PROCEDURE sp_test3()
BEGIN
DECLARE DONE INT DEFAULT 0;
DECLARE col1 varchar(255);
DECLARE curA CURSOR FOR SELECT  a1 FROM table_a;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET DONE = 1;
OPEN curA;
SET @SQL_TXT = '';
while done = 0 do  
fetch next from CurA into col1;
if done = 0 then
SET @xxx = CONCAT("select b1 into @yyy  from table_b where b1 ='", 
col1,"'");
PREPARE stmt_name FROM @xxx;
EXECUTE stmt_name;
DEALLOCATE PREPARE stmt_name;
SELECT  @yyy;
END IF;
END WHILE;
close curA;
end
$$

在下面创建表脚本： 

      create table table_a(a1 varchar(255));      
      create table table_b(b1 varchar(255));    

      insert into table_a values('col2');
      insert into table_a values('col3');
      insert into table_a values('col5');
      insert into table_a values('col1');

      insert into table_b values('col2');
      insert into table_b values('col3');
      insert into table_b values('col4');
      insert into table_b values('col1');

标签： mysqlstored-procedurescursor

解决方案

drop procedure if exists sp_test3;
drop table if exists table_b, table_a;

create table if not exists table_a(a1 varchar(255));
create table if not exists table_b(b1 varchar(255));

insert into table_a values ('col2');
insert into table_a values ('col3');
insert into table_a values ('col5');
insert into table_a values ('col1');

insert into table_b values ('col2');
insert into table_b values ('col3');
insert into table_b values ('col4');
insert into table_b values ('col1');

 CREATE PROCEDURE sp_test3()
 BEGIN
 DECLARE DONE, DONE1 INT DEFAULT 0;
 DECLARE col1 varchar(255);
 DECLARE curA CURSOR FOR SELECT a1 FROM table_a;
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET DONE = 1;
 OPEN curA;
 SET @SQL_TXT = '';
    while done = 0 do  
     fetch next from CurA into col1;
     if done = 0 then
     BEGIN
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET DONE1 = 1;
     SET @xxx = CONCAT("select b1 into @yyy 
                       from table_b
                       where b1 = '", col1, "'");
     PREPARE stmt_name FROM @xxx;
     EXECUTE stmt_name;
     DEALLOCATE PREPARE stmt_name;
     if (DONE1 = 0) THEN
       SELECT @yyy;
     ELSE
       SET DONE1 = 0;
     END IF;
     END;
     END IF;
   END WHILE;
  close curA;
 end;

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