php - 带左连接的 Mysql 查询 - 如果两行相同则专用索引

Question

我的 mysql 数据库中有一个名为 users 的表和另一个名为 grouppost 的表。两个表都有共同的 id 行。因此，当我对两个表进行左连接的 sql 查询时，如何决定我想要哪个 id 行？

示例

$sql = "SELECT gp.*, u.*
      FROM grouppost
      AS gp LEFT JOIN users AS u ON u.username = gp.author
      WHERE gp.gname = ? AND gp.type = ? ORDER BY gp.pdate DESC $limit";
      $stmt = $conn->prepare($sql);
      $stmt->bind_param("ss",$g,$zero);
      $stmt->execute();
      $result_new = $stmt->get_result();
      if ($result_new->num_rows > 0){
         while ($row = $result_new->fetch_assoc()) {
            $grouppost_id = $row["id"]; // I want to get the id from table grouppost but I get the id from the users table
         }
      }

Answer 1

如果您想在结果集中单独定位它，您可以在选择中为其指定别名:

SELECT gp.*, u.*, gp.id AS grouppost_id 
FROM grouppost AS gp 
LEFT JOIN users AS u ON u.username = gp.author
WHERE gp.gname = ? 
  AND gp.type = ? 
ORDER BY gp.pdate DESC
$limit