從數據庫中選擇項目與另一個表中的最新日期進行比較

Question

我想從userLogTable中選擇所有記錄，其中記錄比activityTable的最新匹配項新。 我想在一個查詢中執行此操作。

目前，我從一個表中進行選擇，然后遍歷結果，同時與另一張表進行匹配。

SELECT COUNT(*) AS Visits, userLogTable.* FROM userLogTable GROUP BY Name, Date

userLogTable
Name   | Surname | Date
-----------------------------
Dave   | Smith   | 2016-06-01
Jane   | Doe     | 2016-06-01
Dave   | Smith   | 2016-06-02
Dave   | Smith   | 2016-06-01
Jane   | Doe     | 2016-06-03
Peter  | Bloggs  | 2016-06-03
Steve  | Foo     | 2016-06-01
Steve  | Foo     | 2016-06-01
// many more rows

// above SQL returns the following result as expected/needed
Name   | Surname |  Date       | Visits
----------------------------------------
Dave   | Smith   |  2016-06-01 | 2
Jane   | Doe     |  2016-06-01 | 1
Dave   | Smith   |  2016-06-02 | 1
Jane   | Doe     |  2016-06-03 | 1
Peter  | Bloggs  |  2016-06-03 | 1
Steve  | Foo     |  2016-06-01 | 2

activityTable
Name   | Surname | Date
------------------------------
Dave   | Smith   | 2016-06-03
Dave   | Smith   | 2016-06-03
Dave   | Smith   | 2016-06-03
Dave   | Smith   | 2016-06-02
Dave   | Smith   | 2016-06-02
Dave   | Smith   | 2016-06-02
Dave   | Smith   | 2016-06-01
Dave   | Smith   | 2016-05-29
Dave   | Smith   | 2016-05-29
// many more rows

查詢：

foreach($userLogTableResult as $key => $val) {
    // db function
    SELECT Date 
    FROM activityTable  
    WHERE Date > $latestDateFromUserLogTable 
      AND NAME = $val['Name'] 
      AND Surname = $val['Surname'] 
    ORDER BY Date DESC LIMIT 1 
    // if there is a result then unset this item as it's older than the latest activity
}

任何幫助將不勝感激。

上面的代碼已針對此示例進行了廣泛簡化。 我正在構建SQL並將其解析為自定義PDO函數。 所有值都將被轉義並進行相應的清理。

Answer 1

我認為這可以滿足您的需求：

select ult.*
from userLogTable ult
where ult.date > (select max(a.date)
                  from activityTable a
                  where a.name = ult.name and a.surname = ult.surname
                 ) ;