如何获得结果集的交点？

编程问答 2022-08-14

问题描述

结果集1：

select code from quote where cond1

结果集2：

select code from vix  where cond2

我想要一个包含code的集合，该集合是Result set1和Result set2的交集。

select code from quote where cond1 and code in (select code from vix  where cond2);

它不起作用！GMB和Akina的答案均显示相同的错误信息。

RROR 1267（HY000）：操作'='的排序规则（utf8mb4_general_ci，IMPLICIT）和（utf8mb4_unicode_ci，IMPLICIT）的非法混合

让我们显示表结构：

show create table quote;
+-------+------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                                                                                                                             |
+-------+-----------------------------------------------------------------
| quote | CREATE TABLE `quote` (
  `id` int(8) unsigned NOT NULL AUTO_INCREMENT,`code` text COLLATE utf8mb4_unicode_ci,`date` date DEFAULT NULL,`open` double DEFAULT NULL,`high` double DEFAULT NULL,`low` double DEFAULT NULL,`close` double DEFAULT NULL,`volume` bigint(20) DEFAULT NULL,PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=17173979 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci |
+-------+--------------------------------------------------------------------+

show create table vix;
+-------+-------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                  |
+-------+--------------------------------------------------------------------+
| vix   | CREATE TABLE `vix` (
  `code` text,`span` smallint(6) DEFAULT NULL,`vix` double DEFAULT NULL,`extrem_date` date DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 |

从表quote和vix中设置的搜索代码。

select code from quote where volume > 10000000 and date='2020-08-24';
+-------+
| code  |
+-------+
| zom   |
| ibio  |

注意：大约120行。

select code from vix  where span >30;
+---------+
| code    |
+---------+
| canf    |
| ensv    |

注意：大约1100行。 获取两个结果集的交集：

MariaDB [stock]> select code 
    -> from quote q 
    -> where 
    ->     volume > 10000000 and date='2020-08-24'
    ->     and exists (select 1 from vix v where span >30 and (v.code = q.code));
ERROR 1267 (HY000): Illegal mix of collations (utf8mb4_general_ci,IMPLICIT) and (utf8mb4_unicode_ci,IMPLICIT) for operation '='

解决方法

您的（伪）查询查询应该执行您想要的操作。但是，我发现，当值列表变大时，使用exists会更有效。我可以这样说：

select code 
from quote q 
where 
    cond1
    and exists (select 1 from vix v where cond2 and v.code = q.code)
, 
SELECT code 
FROM (select code from quote where cond1) q1
JOIN (select code from vix   where cond2) q2 USING (code)
, 
// iterate over all files in the 'templates' folder INSIDE the .exe
each(fs.readdirSync('templates'),(filename: string) => {
  const dataBuffer = fs.readFileSync(`templates/${filename}`);
  // do sth with that file data,e.g. export it to some location (outside the .exe)
  const stream = fs.createWriteStream(`${outDir}/${filename}`);
  stream.write(dataBuffer );
  stream.close();
});
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