SQL元相关查询

Question

你好我在mysql表中有2个表和post_meta表 我想根据post_meta键/值数据查询post表。 带有= statment的示例中的第一个查询正在运行，第二个查询带有！= statment无法正常工作。有帮助吗？

如何排除包含postmeta键的帖子[hide] = value ['1']？

这里有期待的结果

例如

//显示postmeta键[hide] = value 1

的帖子

SELECT
    *
FROM
    post AS mt0
INNER JOIN post_meta AS mt1 ON mt0.id = mt1.postid
WHERE
    (
        mt1.`key` = 'hide'
        AND CAST(mt1.`value` AS CHAR) = 1
    )

2行
1后测试1 3 1隐藏1

3后测试3 4 3隐藏1

//显示postmeta键的位置[hide]！= value 1

SELECT
    *
FROM
    post AS mt0
INNER JOIN post_meta AS mt1 ON mt0.id = mt1.postid
WHERE
    (
        mt1.`key` = 'hide'
        AND CAST(mt1.`value` AS CHAR) != 1
    )

0行

//为什么呢？此查询必须返回帖子2

数据库架构

----table post

CREATE TABLE `post` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `title` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;


INSERT INTO `post` VALUES ('1', 'Post test 1');
INSERT INTO `post` VALUES ('2', 'Post test 2');
INSERT INTO `post` VALUES ('3', 'Post test 3');


----table post_meta

CREATE TABLE `post_meta` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `postid` int(11) DEFAULT NULL,
  `key` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `value` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

INSERT INTO `post_meta` VALUES ('1', '1', 'name', 'leone');
INSERT INTO `post_meta` VALUES ('2', '2', 'name', 'mario');
INSERT INTO `post_meta` VALUES ('3', '1', 'hide', '1');
INSERT INTO `post_meta` VALUES ('4', '3', 'hide', '1');

Answer 1

由于条件

，第二个查询不起作用

mt1.`key` = 'hide'

仔细查看查询

SELECT
    *
FROM
    post AS mt0
INNER JOIN post_meta AS mt1 ON mt0.id = mt1.postid
WHERE
    (
        mt1.`key` = 'hide'
        AND CAST(mt1.`value` AS CHAR) != 1
    )

您的条件为

mt1.`key` = 'hide'

然后你正在使用

AND CAST(mt1.`value` AS CHAR) != 1

现在在post_meta表格中检查没有数据

key = hide and value != '1'

因此条件失败，你得到0结果

以下是您提供的内容

INSERT INTO `post_meta` VALUES ('1', '1', 'name', 'leone');
INSERT INTO `post_meta` VALUES ('2', '2', 'name', 'mario');
INSERT INTO `post_meta` VALUES ('3', '1', 'hide', '1');
INSERT INTO `post_meta` VALUES ('4', '3', 'hide', '1');

根据问题中提供的更新，您可以获得结果

SELECT *
FROM
post AS mt0
INNER JOIN post_meta mt1
ON mt0.id = mt1.postid
AND mt0.id NOT IN (
  select postid from post_meta where `key` = 'hide' AND CAST(`value` AS CHAR) = 1
);

<强> DEMO