Question

以下查询效果很好。现在我想添加另一个名为地址的表格，其中包含相同的submissionid和zip变量。我想从地址中提取所有submissionid变量zip = '$zip'，然后使用这些结果从提交中查找相应的title行表格在下面的查询中。

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

Answer 1

您可以使用子查询

来实现此目的

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

参考：IN Subquery

或使用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";

参考：JOIN

正如评论中提到的@AdrianCornish，INNER连接比子查询更快。所以你最好选择加入第二个选项。

SO Subqueries vs joins

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