Mysql 避免在内部选择中进行全表扫描

我在MySQL中有以下select，它可以产生正确的结果，但需要花费不必要的时间来执行：

SELECT tblGPSDevices.Email, tblLoc.Lat, tblLoc.Lon, tblLoc.Radius, tblLoc.CreationTimeStamp, tblTrackedUsers.ID, tblTrackedUsers.TrackerDeviceID, tblTrackedUsers.TrackedDeviceID
    FROM tblTrackedUsers
    INNER JOIN tblGPSDevices ON tblTrackedUsers.TrackedDeviceID = tblGPSDevices.ID
    LEFT OUTER JOIN (
            SELECT A.DeviceID, A.Lat, A.Lon, A.Radius, A.CreationTimeStamp, A.ID 
            FROM tblLocations A 
            INNER JOIN (
                    SELECT DeviceID, MAX(CreationTimeStamp) AS CreationTimeStamp, MAX(ID) AS ID
                    FROM tblLocations
                    GROUP BY DeviceID
            ) AS B ON A.DeviceID = B.DeviceID
                AND A.CreationTimeStamp = B.CreationTimeStamp
                AND A.ID = B.ID                         
    ) AS tblLoc ON tblLoc.DeviceID = tblGPSDevices.ID
    WHERE tblGPSDevices.Validated = 0x01
    AND tblGPSDevices.Enabled = 0x01
    AND tblTrackedUsers.Validated = 0x01
    AND tblTrackedUsers.TrackerDeviceID = 1
    ORDER BY tblTrackedUsers.ID;

此查询的运行速度要慢得多，因为它对tblLocations执行完整的表扫描

这是真正减慢查询速度的部分：

SELECT A.DeviceID, A.Lat, A.Lon, A.Radius, A.CreationTimeStamp, A.ID 
        FROM tblLocations A 
        INNER JOIN (
            SELECT DeviceID, MAX(CreationTimeStamp) AS CreationTimeStamp, MAX(ID) AS ID
            FROM tblLocations
            GROUP BY DeviceID
        ) AS B ON A.DeviceID = B.DeviceID
            AND A.CreationTimeStamp = B.CreationTimeStamp
            AND A.ID = B.ID 

以下是解释计划：

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
1   PRIMARY     tblTrackedUsers     ref     TrackerDeviceID,TrackedDeviceID     TrackerDeviceID     9   const   14  Using where; Using temporary; Using filesort
1   PRIMARY     tblGPSDevices   eq_ref  PRIMARY     PRIMARY     8   tblTrackedUsers.TrackedDeviceID     1   Using where
1   PRIMARY     <derived2>  ALL     NULL    NULL    NULL    NULL    2073    
2   DERIVED     <derived3>  ALL     NULL    NULL    NULL    NULL    2073    
2   DERIVED     A   eq_ref  PRIMARY,DeviceID,CreationTimeStampIndex     PRIMARY     8   B.ID    1   Using where
3   DERIVED     tblLocations    index   NULL    DeviceID    8   NULL    174058  

但不幸的是，TBLTrackDusers.TrackedDeviceID在内部select中不可见。如果我加上

WHERE DeviceID = tblTrackedUsers.TrackedDeviceID

正上方

GROUP BY DeviceID

它不起作用

如何优化此查询

仅涉及相关字段的表的结构：

TBLGPS设备：

---

ID |电子邮件|已验证|已启用

---

t分配：

---

ID |设备ID | Lat | Lon |半径| CreationTimeStamp

---

tblTrackedUsers：

---

ID | TrackerDeviceID | TrackedDeviceID |已验证

---

tblLocations.DeviceID、tblTrackedUsers.TrackerDeviceID和tblTrackedUsers.TrackedDeviceID是指向tblGPSDevices.ID的外键

此查询的作用是：

---

查询应返回用户正在跟踪的tblGPSDevices中的所有设备以及它们在tblLocations中的最后位置。确定用户正在跟踪哪些设备的方法由TBLTrackDusers确定：从TBLTrackDusers中选择TrackedDeviceID，其中TrackerDeviceID=some_value

我自己找到了答案，我将发布以供将来参考。这使查询速度从2秒加快。到0.0179秒。这是一个巨大的收获

关键是在以下内容中再添加一个内部选择：

SELECT DeviceID, MAX(CreationTimeStamp) AS CreationTimeStamp, MAX(ID) AS ID
FROM tblLocations
GROUP BY DeviceID

为了避免全表扫描，因为我们只对tblTrackedUsers.TrackedDeviceID=的DeviceID感兴趣。现在，此选择如下所示：

 SELECT C.DeviceID, MAX(C.CreationTimeStamp) AS CreationTimeStamp, MAX(C.ID) AS ID
 FROM tblLocations C
         INNER JOIN (
              SELECT ID, TrackerDeviceID, TrackedDeviceID,  TrackedName, AccessCode, Validated FROM tblAllowedUsers WHERE TrackerDeviceID = 1 AND Validated=0x01
          ) AS D ON D.TrackedDeviceID = C.DeviceID
  GROUP BY DeviceID

以下是“立即选择”的完整选项：

SELECT tblGPSDevices.Email, tblLoc.Lat, tblLoc.Lon, tblLoc.Radius, tblLoc.CreationTimeStamp, tblTrackedUsers.ID, tblTrackedUsers.TrackerDeviceID, tblTrackedUsers.TrackedDeviceID
    FROM tblTrackedUsers
    INNER JOIN tblGPSDevices ON tblTrackedUsers.TrackedDeviceID = tblGPSDevices.ID
    LEFT OUTER JOIN (
            SELECT A.DeviceID, A.Lat, A.Lon, A.Radius, A.CreationTimeStamp, A.ID 
            FROM tblLocations A 
            INNER JOIN (
                SELECT C.DeviceID, MAX(C.CreationTimeStamp) AS CreationTimeStamp, MAX(C.ID) AS ID
            FROM tblLocations C
                INNER JOIN (
                    SELECT ID, TrackerDeviceID, TrackedDeviceID,  TrackedName, AccessCode, Validated FROM tblAllowedUsers WHERE TrackerDeviceID = 1 AND Validated=0x01
                ) AS D ON D.TrackedDeviceID = C.DeviceID
            GROUP BY DeviceID
            ) AS B ON A.DeviceID = B.DeviceID
                AND A.CreationTimeStamp = B.CreationTimeStamp
                AND A.ID = B.ID                         
    ) AS tblLoc ON tblLoc.DeviceID = tblGPSDevices.ID
    WHERE tblGPSDevices.Validated = 0x01
    AND tblGPSDevices.Enabled = 0x01
    AND tblTrackedUsers.Validated = 0x01
    AND tblTrackedUsers.TrackerDeviceID = 1
    ORDER BY tblTrackedUsers.ID;

---

您能给出您正在查询的表的模式吗？并说明查询需要执行的操作do@czifro我已经用必需的信息更新了这个问题，以便更好地发布createtable和INSERT命令或创建sqlfiddle。下次当你发布这样一个问题的时候，请发布SQL来处理它。它也许对你有所帮助，但它并不像最初提出的那样真正回答了你的问题。要给出这样的答案，你必须拥有超自然的精神力量（不知道你的实际数据）。我也怀疑它是否是最理想的方法。@VDohnal我不知道SQLFiddle。只是检查了一下，我同意，在那里创建表会很有帮助。我只是看了一下你编辑过的答案，本来会给你一些信任的，但是你的SQL执行了17.8766秒。如果您正在寻找性能，则不应使用where field=（选择field…）。最好是进行内部联接。另外，sintax是tlsql而不是MySQL。但这并不重要。不过我非常感谢你的帮助。从别人那里提出想法总是有益的。

SELECT tblGPSDevices.Email, tblLoc.Lat, tblLoc.Lon, tblLoc.Radius, tblLoc.CreationTimeStamp, tblTrackedUsers.ID, tblTrackedUsers.TrackerDeviceID, tblTrackedUsers.TrackedDeviceID
    FROM tblTrackedUsers
    INNER JOIN tblGPSDevices ON tblTrackedUsers.TrackedDeviceID = tblGPSDevices.ID
    LEFT OUTER JOIN (
            SELECT A.DeviceID, A.Lat, A.Lon, A.Radius, A.CreationTimeStamp, A.ID 
            FROM tblLocations A 
            INNER JOIN (
                SELECT C.DeviceID, MAX(C.CreationTimeStamp) AS CreationTimeStamp, MAX(C.ID) AS ID
            FROM tblLocations C
                INNER JOIN (
                    SELECT ID, TrackerDeviceID, TrackedDeviceID,  TrackedName, AccessCode, Validated FROM tblAllowedUsers WHERE TrackerDeviceID = 1 AND Validated=0x01
                ) AS D ON D.TrackedDeviceID = C.DeviceID
            GROUP BY DeviceID
            ) AS B ON A.DeviceID = B.DeviceID
                AND A.CreationTimeStamp = B.CreationTimeStamp
                AND A.ID = B.ID                         
    ) AS tblLoc ON tblLoc.DeviceID = tblGPSDevices.ID
    WHERE tblGPSDevices.Validated = 0x01
    AND tblGPSDevices.Enabled = 0x01
    AND tblTrackedUsers.Validated = 0x01
    AND tblTrackedUsers.TrackerDeviceID = 1
    ORDER BY tblTrackedUsers.ID;