Question

我的数据库中有2个表格，我想比较每个查询的2个选择查询的值

表1：click_log

查询表1：

SELECT *
FROM click_log

表2：km_articles

查询表2：

SELECT km_article_no
FROM km_articles
WHERE  km_article_date <= "2017-10-31" AND km_article_status = "Published" AND km_article_view_count <= "5"

我要比较的列是表link1clicked for table 1 with km_article_no我知道我会发现重复匹配，然而从那些重复的匹配我想找到我想要从表1中的另一列调用的最新一个＆＃34; when_clicked＆＃34;包含数据信息，不确定如何将这些信息放在一起进行查询，然后缩小范围。

这就是表格的样子：

表1：

|link_clicked|when_clicked
     KB00001 | 2017-08-02
     KB00001 | 2017-12-02
     KB00002 | 2017-08-02
     KB00002 | 2017-09-02
     KB00003 | 2017-09-02
     KB00003 | 2017-09-02

表2：

km_article_no|km_article_ti|km_article_status|km_article_view_count|km_article_date
  KB00001    |outlook IOS  |  Published      |         5           | 2017-01-02
  KB00002    |outlook CSS  |  Published      |         4           | 2017-01-05
  KB00003    |outlook ZTE  |   Retired       |         3           | 2017-01-09

Answer 1

如果我理解正确，您希望显示所有km_articles行，每行都包含最新的相关click_log.when_clicked日期。因此，按click_log汇总link_clicked并找到最大值when_clicked。然后将其加入km_articles。

select kma.*, cl.last_clicked
from km_articles kma
join
(
  select link_clicked, max(when_clicked) as last_clicked
  from click_log
  group by link_clicked
) cl on cl.link_clicked = kma.km_article_no
where kma.km_article_date <= date '2017-10-31'
  and kma.km_article_status = 'Published'
  and kma.km_article_view_count <= 5;

（如果您还希望在km_articles中显示不匹配的click_log行，请将join更改为left join。）

在2个表

1 个答案: