mysql - 查询优化——花费太长时间并停止服务器

Question

我的查询生成一些关于超速、上次和平均速度的报告。 这是我的查询:

Select 
    r1 . *, r2.name, r2.notes, r2.serial
From
    (SELECT 
        k.idgps_unit,
            MIN(k.dt) AS DT_Start,
            MIN(CASE
                WHEN k.RowNumber = 1 THEN k.Lat
            END) AS Latitude_Start,
            MIN(CASE
                WHEN k.RowNumber = 1 THEN k.Long
            END) AS Longitude_Start,
            MIN(CASE
                WHEN k.RowNumber = 1 THEN k.Speed_kmh
            END) AS Speed_Start,
            MAX(k.dt) AS dt_end,
            MIN(CASE
                WHEN k.RowNumber = MaxRowNo THEN k.Lat
            END) AS Latitude_End,
            MIN(CASE
                WHEN k.RowNumber = MaxRowNo THEN k.Long
            END) AS Longitude_End,
            MIN(CASE
                WHEN k.RowNumber = MaxRowNo THEN k.Speed_kmh
            END) AS Speed_End,
            AVG(Speed_kmh) AS Average_Speed
    FROM
        (SELECT 
        gps_unit_location . *,
            @i:=CASE
                WHEN Speed_Kmh > 80 AND @b = 0 THEN @i + 1
                ELSE @i
            END AS IntervalID,
            @r:=CASE
                WHEN Speed_Kmh > 80 AND @b = 0 THEN 1
                ELSE @r + 1
            END AS RowNumber,
            @b:=CASE
                WHEN Speed_Kmh > 80 THEN 1
                ELSE 0
            END AS IntervalCheck
    FROM
        gps_unit_location, (SELECT @i:=0) i, (SELECT @r:=0) r, (SELECT @b:=0) b
    ORDER BY dt , idgps_unit_location) k
    INNER JOIN (SELECT 
        IntervalID, MAX(RowNumber) AS MaxRowNo
    FROM
        (SELECT 
        gps_unit_location . *,
            @i:=CASE
                WHEN Speed_Kmh > 80 AND @b = 0 THEN @i + 1
                ELSE @i
            END AS IntervalID,
            @r:=CASE
                WHEN Speed_Kmh > 80 AND @b = 0 THEN 1
                ELSE @r + 1
            END AS RowNumber,
            @b:=CASE
                WHEN Speed_Kmh > 80 THEN 1
                ELSE 0
            END AS IntervalCheck
    FROM
        gps_unit_location, (SELECT @i:=0) i, (SELECT @r:=0) r, (SELECT @b:=0) b
    ORDER BY dt , idgps_unit_location) d
    WHERE
        IntervalCheck = 1
    GROUP BY IntervalID) MaxInt ON MaxInt.IntervalID = k.IntervalID
    WHERE
        k.IntervalCheck = 1
            and k.idgps_unit in (SELECT 
                idgps_unit
            FROM
                instafleet.gps_unit
            where
                id_customer = (select 
                        idcustomer
                    from
                        user
                    where
                        iduser = 14))
    GROUP BY k.IntervalID , k.idgps_unit) r1
        Inner join
    gps_unit r2 ON r1.idgps_unit = r2.idgps_unit

目前783,723条记录需要3分钟。我认为适当的索引可能会有所帮助；尽管经过反复试验，我无法弄清楚。如果您认为自己可以提供帮助，并且需要一些额外的信息 - 我很乐意为您提供。

解释

结果

Answer 1

添加索引在很多情况下都有帮助，但是您有一个子查询加入另一个子查询，当前表上没有索引可以帮助您加快速度。您可以在此处使用索引的唯一方法是创建临时表。

因此，正如 Markus 指出的那样，您需要将查询分成几个较小的查询，将它们的结果存储在一个临时表中。比您可以向它们添加索引并希望加速您的查询。将大查询分解为几个较小的查询的另一个好处是，您可以更好地分析哪部分是较慢的部分并修复它。

您还使用了一个子查询两次，这对性能不利，因为结果未被缓存。

这是一个如何做到这一点的例子:

DROP TEMPORARY TABLE IF EXISTS tmp_k;
CREATE TEMPORARY TABLE tmp_k
    ENGINE=Memory
SELECT 
    gps_unit_location.*,
    @i:= IF(((Speed_Kmh > 80) AND (@b = 0)), @i + 1, @i) AS IntervalID,
    @r:= IF(((Speed_Kmh > 80) AND (@b = 0)), 1, @r + 1) AS RowNumber,
    @b:= IF((Speed_Kmh > 80), 1, 0) AS IntervalCheck
FROM
    gps_unit_location,
    (SELECT @i:=0) i, 
    (SELECT @r:=0) r, 
    (SELECT @b:=0) b
ORDER BY
    dt,
    idgps_unit_location;

ALTER TABLE tmp_k ADD INDEX (IntervalID);

DROP TEMPORARY TABLE IF EXISTS tmp_max;
CREATE TEMPORARY TABLE tmp_max
    ENGINE=Memory
SELECT 
    IntervalID, 
    MAX(RowNumber) AS MaxRowNo
FROM
    temp_k
WHERE
    IntervalCheck = 1
GROUP BY 
    IntervalID;

ALTER TABLE tmp_max ADD INDEX (IntervalID);

SELECT 
    k.idgps_unit,
    MIN(k.dt) AS DT_Start,
    MIN(IF(k.RowNumber = 1, k.Lat, NULL)) AS Latitude_Start,
    MIN(IF(k.RowNumber = 1, k.Long, NULL)) AS Longitude_Start,
    MIN(IF(k.RowNumber = 1, k.Speed_kmh, NULL) AS Speed_Start,
    MAX(k.dt) AS DT_End,
    MIN(IF(k.RowNumber = m.MaxRowNo, k.Lat, NULL)) AS Latitude_End
    MIN(IF(k.RowNumber = m.MaxRowNo, k.Long, NULL)) AS Longitude_End
    MIN(IF(k.RowNumber = m.MaxRowNo, k.Speed_kmh, NULL)) AS Speed_End,
    AVG(Speed_kmh) AS Average_Speed,
    gu.name,
    gu.notes,
    gu.serial
FROM
    tmp_k AS k
    INNER JOIN tmp_max AS m
        USING(IntervalID)
    INNER JOIN gps_unit AS gu
        USING(idgps_unit)
    INNER JOIN user AS u
    ON (gu.idcustomer = u.idcustomer)
WHERE
    (k.IntervalCheck = 1) 
     AND (u.iduser = 14)
GROUP BY 
    k.IntervalID, 
    k.idgps_unit;

DROP TEMPORARY TABLE tmp_k;
DROP TEMPORARY TABLE tmp_max;