Php 循环内的SQL查询

我有一个问题，在foreach循环中执行db查询

导致性能问题

            <?php 
            $conn=$database->openConnection();

            $stmt=$conn->query('SELECT id,uuid,banned_by_uuid,until FROM bans WHERE active = 1');
            $s = microtime(true);
            foreach($stmt as $row){

                $playerName=current($conn->query('SELECT Playername FROM SYSTEM WHERE UUID="'.$row['uuid'].'"')->fetch());
                $playerNameBannedBy=current($conn->query('SELECT Playername FROM SYSTEM WHERE UUID="'.$row['banned_by_uuid'].'"')->fetch());
                $playerNamePrint=$playerName == null ? 'Undefined' : htmlspecialchars($playerName);
                $playerBannerPrint=$playerNameBannedBy == null ? 'Undefined' : htmlspecialchars($playerNameBannedBy);

                echo '<tr><td>'.$row['id'].'</td><td>'.$playerNamePrint.'</td><td>'.$playerBannerPrint.'</td><td><i class="material-icons">access_time</i> '.ago($row['until']).'</td><td><button class="btn btn-icon white" onClick="getReason('.$row['id'].')" data-toggle="tooltip" data-placement="top" data-original-title="Click here to see Ban Reason"><i class="material-icons">info</i></button></td></tr>';
            }
            $e = microtime(true);
        ?>

---

您可以通过一次查询获得所有结果

    SELECT b.id,b.uuid,b.banned_by_uuid,b.until, sa.Playername, sb.Playername banned
    FROM bans b
    INNER JOIN SYSTEM sa on sa.UUID = b.uuid 
    INNER JOIN SYSTEM sb on sb.UUID = b.banned_by_uuid 
    WHERE b.active = 1 

您可以通过单个查询获得所有结果

    SELECT b.id,b.uuid,b.banned_by_uuid,b.until, sa.Playername, sb.Playername banned
    FROM bans b
    INNER JOIN SYSTEM sa on sa.UUID = b.uuid 
    INNER JOIN SYSTEM sb on sb.UUID = b.banned_by_uuid 
    WHERE b.active = 1 

是的，如果bans表中有许多记录，那么每个返回的记录再执行两个查询肯定会导致问题

尝试使用连接，如下所示：

SELECT id,uuid,banned_by_uuid,until, banned_players.Playername banner_player_name, banned_by_players.Playername banned_by_player_name
FROM bans
INNER JOIN SYSTEM banned_players ON banned_players.uuid = bans.uuid
INNER JOIN SYSTEM banned_by_players ON banned_by_players.uuid = bans.banned_by_uuid
WHERE active = 1

是的，如果bans表中有许多记录，那么每个返回的记录再执行两个查询肯定会导致问题

尝试使用连接，如下所示：

SELECT id,uuid,banned_by_uuid,until, banned_players.Playername banner_player_name, banned_by_players.Playername banned_by_player_name
FROM bans
INNER JOIN SYSTEM banned_players ON banned_players.uuid = bans.uuid
INNER JOIN SYSTEM banned_by_players ON banned_by_players.uuid = bans.banned_by_uuid
WHERE active = 1

您可以使用此查询

SELECT (CASE WHEN s.uuid = b.uuid THEN 1 ELSE 0 END) AS Separator, s.*
FROM system AS s JOIN bans AS b 
                ON s.uuid = b.uuid OR s.uuid = banned_by_uuid
WHERE b.active = 1

您可以使用分隔列了解两个结果之间的差异。
您可以使用此查询

SELECT (CASE WHEN s.uuid = b.uuid THEN 1 ELSE 0 END) AS Separator, s.*
FROM system AS s JOIN bans AS b 
                ON s.uuid = b.uuid OR s.uuid = banned_by_uuid
WHERE b.active = 1

您可以通过使用分隔列了解两个结果之间的差异