更改查詢以從輔助表添加結果

Question

以下查詢運行良好。現在我想添加另一個表，名稱爲地址，其中包含與下面相同的submissionid和zip變量。我想從地址其中zip = '$zip'中抽取所有submissionid變量，然後使用這些結果在下面的查詢中從提交表中查找對應的title行。

$sqlStr = "SELECT title, points, submissionid 
      FROM submission 
      WHERE zip = '$zip' 
     ORDER BY points DESC, title ASC    
    LIMIT $offset, $rowsperpage"; 

Answer 1

可以acheve此使用子查詢

$sqlStr = "SELECT title, points, submissionid 
     FROM submission 
     WHERE submissionid IN(
       SELECT submissionid 
       FROM addreses 
       WHERE zip = '$zip') 
    ORDER BY points DESC, title ASC    
LIMIT $offset, $rowsperpage"; 

參考：IN Subquery

或者與JOIN

$sqlStr = "SELECT s.title, s.points, s.submissionid 
     FROM submission s 
     INNER JOIN addresses ad 
     on ad.submissionid = s.submissionid 
     WHERE ad.zip = '$zip' 
    ORDER BY s.points DESC, s.title ASC    
LIMIT $offset, $rowsperpage"; 

參考：JOIN

而@AdrianCornish在評論中提到INNER連接速度快於子查詢。所以你最好用JOIN去做第二個選擇。

SO上的相關線程Subqueries vs joins