从一个数组开始，该数组保存进入名为producttags的数据库表中的值。
$newproducttags = array ('Green', 'Synthetic', 'Clearance');
和另一个变量，该变量将其Foreign Key ID连接到另一个名为products的表
看起来与此类似
╔═════╦═══════╦═════════════════════╗
║ id ║ MPN ║ createdtime ║
╠═════╬═══════╬═════════════════════╣
║ ... ║ ... ║ ... ║
║ 517 ║ 0WV12 ║ 2019-01-05 02:42:33 ║
║ ... ║ ... ║ ... ║
╚═════╩═══════╩═════════════════════╝
/
// in this case $fk_id = 517;
$fk_id = $this->db->run("SELECT id FROM `products` WHERE `MPN` = ?", [$MPN])->fetchColumn();
在执行查询SELECT * FROM producttags WHERE productID = 517时，它会带回
╔═══════════╦══════════════╦═════════════════════╗
║ productID ║ Tag ║ lastmodified ║
╠═══════════╬══════════════╬═════════════════════╣
║ 517 ║ Blue ║ 2019-02-02 15:00:23 ║
║ 517 ║ Synthetic ║ 2019-02-02 15:00:23 ║
║ 517 ║ Monthly Sale ║ 2019-02-02 15:00:23 ║
╚═══════════╩══════════════╩═════════════════════╝
我试图用$newproducttags的内容创建一个临时表，然后将其与当前现有的producttags表进行比较。
这样做很容易。
CREATE TEMPORARY TABLE producttags_temp AS
SELECT Tag AS Tag_temp, productID AS productID_temp,
lastmodified AS lastmodified_Temp FROM producttags LIMIT 0;
使用foreach循环将$newproducttags中的值中的新产品标签插入到临时表中
foreach ($prodTagArr as $prodTag) {
$this->data = $this->db->run("INSERT INTO `producttags_temp`
(`Tag_temp`, `productID_temp`, `lastmodified_Temp`)
VALUES (?, ?, NOW())",
[$prodTag, $fk_id]);
}
这按预期工作。进行SELECT * FROM producttags_temp会返回：
╔═════════╦════════════╦═════════════════════╗
║ id_temp ║ Tag_temp ║ lastmodified_temp ║
╠═════════╬════════════╬═════════════════════╣
║ 517 ║ Green ║ 2019-02-03 12:00:55 ║
║ 517 ║ Synthetic ║ 2019-02-03 12:00:55 ║
║ 517 ║ Clearance ║ 2019-02-03 12:00:55 ║
╚═════════╩════════════╩═════════════════════╝
到目前为止看起来不错，对吧？
现在面临比较上面说明的两个表并输出两者之间的比较的挑战。
我发誓这应该很容易。看起来应该很容易。我想要的输出是这样的 （或者producttags和producttags_temp表上的NULL值也很好-只是可以向我显示当前比较的输出和新的。
这样，但不必一定是这样：
╔═══════════╦══════════════╦════════╦═════════════════════╗
║ productID ║ Tag ║ status ║ lastmodified ║
╠═══════════╬══════════════╬════════╬═════════════════════╣
║ 517 ║ Blue ║ 0 ║ 2019-02-02 15:00:23 ║
║ 517 ║ Monthly Sale ║ 0 ║ 2019-02-02 15:00:23 ║
║ 517 ║ Green ║ 1 ║ 2019-02-03 12:00:55 ║
║ 517 ║ Synthetic ║ 1 ║ 2019-02-03 12:00:55 ║
║ 517 ║ Clearance ║ 1 ║ 2019-02-03 12:00:55 ║
╚═══════════╩══════════════╩════════╩═════════════════════╝
我不知道你们都希望我在尝试失败的过程中混淆线程。
SELECT * FROM producttags_temp WHERE producttags_temp.Tag_temp
NOT IN ( SELECT producttags.Tag FROM producttags
WHERE producttags.productID = producttags_temp.productID_temp );
设法恢复producttags_temp / $newproducttags
╔════════════════╦═══════════╦═════════════════════╗
║ productID_temp ║ Tag_temp ║ lastmodified_temp ║
╠════════════════╬═══════════╬═════════════════════╣
║ 517 ║ Green ║ 2019-02-03 12:00:55 ║
║ 517 ║ Clearance ║ 2019-02-03 12:00:55 ║
╚════════════════╩═══════════╩═════════════════════╝
我假设需要某种JOIN，但是我很难找到可行的解决方案。该查询有效，但不包含任何Tag_temp值，仅包含预先存在的非临时表行。
SELECT * FROM producttags_temp
WHERE producttags_temp.Tag_temp
IN ( SELECT producttags.Tag FROM producttags
WHERE producttags.productID = producttags_temp.productID_temp )
//像这样，但没有时间戳
╔═══════════╦══════════════╗
║ productID ║ Tag ║
╠═══════════╬══════════════╣
║ 517 ║ Blue ║
║ 517 ║ Monthly Sale ║
║ 517 ║ Synthetic ║
║ 517 ║ Blue ║
║ 517 ║ Monthly Sale ║
║ 517 ║ Synthetic ║
║ 517 ║ Blue ║
║ 517 ║ Monthly Sale ║
║ 517 ║ Synthetic ║
╚═══════════╩══════════════╝
这似乎应该是一个非常简单的联接，但是我已经尝试了几种不同的选项，但似乎没有一个提供我想要的输出。任何人都可以对此有所了解，这有点令人发疯:) 谢谢。
答案 0 :(得分：0)
我认为此查询将为您提供所需的结果。它首先创建producttags和producttags_temp中所有标签的列表，并使用LEFT JOIN将其producttags到producttags_temp和COALESCE。从producttags_temp中选择值要优先于producttags中的值（对于两个表中都存在标签的情况）。通过检查productId_temp中的producttags_temp值是否不是NULL来创建状态值，这表明在该表中找到了较新的条目。
SELECT
COALESCE(p2.productId_temp, p1.productId) AS productId,
COALESCE(p2.Tag_temp, p1.Tag) AS Tag,
p2.productId_temp IS NOT NULL AS status,
COALESCE(p2.lastmodified_temp, p1.lastmodified) AS lastmodified
FROM (SELECT Tag FROM producttags
UNION
SELECT Tag_temp FROM producttags_temp
) t
LEFT JOIN producttags p1 ON p1.Tag = t.Tag
LEFT JOIN producttags_temp p2 ON p2.Tag_temp = t.Tag
ORDER BY status
输出：
productId Tag status lastmodified
517 Blue 0 2019-02-02 15:00:23
517 Monthly Sale 0 2019-02-02 15:00:23
517 Green 1 2019-02-03 12:00:55
517 Synthetic 1 2019-02-03 12:00:55
517 Clearance 1 2019-02-03 12:00:55
更新
由于producttags_temp是一个临时表，因此在MySQL查询中不能多次使用它。只要lastmodified日期在该表中晚于producttags，您就可以使用以下查询代替
SELECT tag_temp as Tag,
productid_temp as productID,
MAX(lastmodified_temp) as lastmodified,
MAX(status)
FROM (SELECT producttags_temp.tag_temp,
producttags_temp.productid_temp,
producttags_temp.lastmodified_temp,
1 AS status
FROM producttags_temp
WHERE productid_temp = 517
UNION ALL
SELECT producttags.tag,
producttags.productid,
producttags.lastmodified,
0 AS status
FROM producttags
WHERE productid = 517) t
GROUP BY tag_temp, productid_temp
ORDER BY lastmodified;
答案 1 :(得分：0)
设法在所有人的帮助下将其整合在一起，似乎具有所需的输出。
-- Temporary Table Creation
CREATE TEMPORARY TABLE producttags_temp AS SELECT Tag AS Tag_temp, productID AS productID_temp, lastmodified AS lastmodified_Temp FROM producttags LIMIT 0;
-- Insert Rows
INSERT INTO `producttags_temp` (`Tag_temp`, `productID_temp`, `lastmodified_Temp`) VALUES ('Green', 517, NOW());
INSERT INTO `producttags_temp` (`Tag_temp`, `productID_temp`, `lastmodified_Temp`) VALUES ('Synthetic', 517, NOW());
INSERT INTO `producttags_temp` (`Tag_temp`, `productID_temp`, `lastmodified_Temp`) VALUES ('Clearance', 517, NOW());
-- Actual Query
SELECT tag_temp as Tag,
productid_temp as productID,
lastmodified_temp as lastmodified,
status
FROM (SELECT producttags_temp.tag_temp,
producttags_temp.productid_temp,
producttags_temp.lastmodified_temp,
1 AS status
FROM producttags_temp
WHERE productid_temp = 517
UNION ALL
SELECT producttags.tag,
producttags.productid,
producttags.lastmodified,
0 AS status
FROM producttags
WHERE productid = 517) t
GROUP BY Tag
ORDER BY lastmodified
输出：
╔══════════════╦════════════════╦═════════════════════╦════════╗
║ Tag ║ productID ║ lastmodified ║ status ║
╠══════════════╬════════════════╬═════════════════════╬════════╣
║ Blue ║ 517 ║ 2019-03-02 23:19:08 ║ 0 ║
║ Monthly Sale ║ 517 ║ 2019-03-02 23:19:08 ║ 0 ║
║ Green ║ 517 ║ 2019-03-08 19:37:46 ║ 1 ║
║ Synthetic ║ 517 ║ 2019-03-08 19:37:46 ║ 1 ║
║ Clearance ║ 517 ║ 2019-03-08 19:37:47 ║ 1 ║
╚══════════════╩════════════════╩═════════════════════╩════════╝