Question

我不确定这是MySQL问题还是PHP问题。如果可以在SQL中解决它的首选。

目前我有以下内容：

$sql=$dbh->prepare("SELECT DISTINCT ToUserID, FromUserID FROM Message WHERE Deleted is NULL AND (ToUserID=? OR FromUserID=?)");
$sql->execute(array($_POST['UserID'], $_POST['UserID']));

$messages = $sql->fetchAll();

MySQL查询可能返回如下内容：

{
      "ToUserID" : "1",
      "1" : "2",
      "0" : "1",
      "FromUserID" : "2"
    },
    {
      "ToUserID" : "2",
      "1" : "1",
      "0" : "2",
      "FromUserID" : "1"
    }

我需要的是能够过滤结果，以便上面两个结果只返回一个。即

if (item1.ToUserID == item2.FromUserID) && (item1. FromUserID == item2.toUserID) {
  remove item2
}

另一个例子：

{
      "ToUserID" : "1",
      "1" : "2",
      "0" : "1",
      "FromUserID" : "2"
    },
    {
      "ToUserID" : "2",
      "1" : "1",
      "0" : "2",
      "FromUserID" : "1"
    },
    {
      "ToUserID" : "3",
      "1" : "1",
      "0" : "2",
      "FromUserID" : "1"
    },
    {
      "ToUserID" : "4",
      "1" : "1",
      "0" : "2",
      "FromUserID" : "1"
    },
    {
      "ToUserID" : "4",
      "1" : "1",
      "0" : "2",
      "FromUserID" : "1"
    }

会变成：

{
      "ToUserID" : "1",
      "1" : "2",
      "0" : "1",
      "FromUserID" : "2"
    },
    {
      "ToUserID" : "3",
      "1" : "1",
      "0" : "2",
      "FromUserID" : "1"
    },
    {
      "ToUserID" : "4",
      "1" : "1",
      "0" : "2",
      "FromUserID" : "1"
    }

Answer 1

无关紧要，我会将默认提取模式更改为PDO_FETCH_ASSOC，这样您就不需要为编号键而烦恼，而这些键只是重复信息。

然后，这些组合

 1  2  User1
 2  3  User2
 2  1  User2

你想要消除User2的第二次出现，因为1-2对已经存在。

您可以通过添加两个计算字段在MySQL中执行此操作：

 SELECT ...
 ... IF (user1 < user2, user1, user2) AS oneUser,
 ... IF (user1 < user2, user2, user1) AS anotherUser,
 ...

现在，两行都将两个额外的字段设置为＆＃34; 1＆＃34;和＆＃34; 2＆＃34;，你可以为这些添加一个明确的约束。

当然你也可以在PHP中这样做：

 // Array
$seen = [ ];
while ($tuple = $rs->fetch()) {
    $key = $tuple['user1id'] < $tuple['user2id']
         ? "{$tuple['user1id']}:{$tuple['user2id']}"
         : "{$tuple['user2id']}:{$tuple['user1id']}";
    if (in_array($key, $seen)) {
         // Ignore this tuple.
         continue;
    }
    // Add combination to seen list
    $seen[] = $key;

    ...
}

从mysql查询过滤结果

1 个答案: