MySQL：超慢SQL

我有一個需要將近8秒才能執行的查詢。我對查詢做了EXPLAIN，但我不知道如何解釋結果。有人可以幫我解決這個問題嗎？下面是EXPLAIN結果：MySQL：超慢SQL

=============================================================================================================================================================================================== 
| id | select_type  | table     | type | possible_keys  | key    | key_len | ref          | rows | Extra      | 
=============================================================================================================================================================================================== 
| 1 | PRIMARY   | <derived2>   | ALL  | (NULL)    | (NULL)   | (NULL) | (NULL)         | 669 | Using filesort    | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
| 2 | DERIVED   | Workflow    | const | PRIMARY    | PRIMARY   | 4  |           | 1 | Using index     | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
| 2 | DERIVED   | DataSource   | ref  | PRIMARY,WorkflowId | WorkflowId  | 4  |           | 1546 | Using where     | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
| 2 | DERIVED   | ReadyLog    | ALL  | DataSourceId   | (NULL)   | (NULL) | (NULL)         | 9463 |        | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
| 2 | DERIVED   | DataSourceActivityLog | eq_ref | PRIMARY,DataSourceId | PRIMARY   | 4  | func         | 1 | Using where     | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
| 2 | DERIVED   | User     | eq_ref | PRIMARY    | PRIMARY   | 4  | my_db.DataSourceActivityLog.UserId  | 1 |        | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
| 3 | DEPENDENT SUBQUERY | DataSourceActivityLog | ref  | DataSourceId   | DataSourceId | 4  | my_db.DataSource.Id      | 1135 | Using where; Using filesort | 
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

如果你需要我的更多信息，請讓我知道。謝謝。

更新1：醜陋的查詢：

SELECT WrappedData.* 
FROM (SELECT DataSource.Id, 
       DataSourceActivityLog.Description, 
       DataSourceActivityLog.UserId, 
       DataSource.Status AS StatusCode, 
       (CASE 
        WHEN User.Name IS NULL THEN 'System' 
        ELSE User.Name 
       END)    AS `Username`, 
       ReadyLog.`Timestamp` AS `Received`, 
       DataSourceActivityLog.`Timestamp` 
     FROM DataSource 
       LEFT JOIN DataSourceActivityLog AS ReadyLog 
       ON ((ReadyLog.DataSourceId = DataSource.Id 
         AND ReadyLog.Description = 'ready') 
         OR (ReadyLog.DataSourceId = DataSource.RootId 
          AND ReadyLog.Description = 'ready')), 
       DataSourceActivityLog 
       LEFT JOIN USER 
       ON USER.Id = DataSourceActivityLog.UserId, 
       Workflow 
     WHERE DataSource.Id IN (138, 139, 140, 141, 
            142, 143, 144, 145, 
            146, 147, 148, 149, 
            150, 151, 152, 153, 
            154, 155, 156, 157, 
            158, 160, 162, 163, 
            166, 167, 169, 170, 
            171, 173, 174, 176, 
            177, 179, 180, 182, 
            183, 185, 186, 187, 
            189, 190, 191, 193, 
            194, 196, 197, 199, 
            200, 201, 203, 204, 
            207, 208, 209, 211, 
            212, 214, 216, 217, 
            219, 221, 222, 223, 
            226, 227, 228, 231, 
            232, 233, 235, 237, 
            238, 242, 243, 240, 
            245, 246, 248, 250, 
            252, 253, 255, 256, 
            258, 259, 261, 263, 
            264, 266, 267, 271, 
            269, 272, 276, 274, 
            277, 280, 282, 284, 
            279, 287, 285, 288, 
            290, 291, 293, 298, 
            301, 299, 303, 304, 
            306, 309, 310, 311, 
            315, 316, 318, 322, 
            323, 325, 329, 330, 
            331, 336, 339, 343, 
            345, 346, 348, 351, 
            352, 354, 356, 357, 
            358, 360, 362, 364, 
            367, 369, 370, 373, 
            375, 376, 378, 381, 
            382, 384, 386, 388, 
            390, 391, 394, 395, 
            397, 400, 402, 404, 
            405, 408, 412, 413, 
            414, 415, 420, 421, 
            424, 425, 429, 430, 
            433, 434, 438, 439, 
            441, 442, 443, 445, 
            446, 447, 449, 451, 
            452, 453, 456, 457, 
            458, 459, 462, 464, 
            465, 466, 470, 473, 
            474, 475, 477, 478, 
            481, 482, 483, 485, 
            487, 488, 489, 491, 
            493, 494, 495, 497, 
            498, 500, 501, 502, 
            504, 505, 507, 508, 
            509, 512, 513, 514, 
            515, 516, 518, 519, 
            520, 521, 522, 524, 
            525, 526, 527, 529, 
            530, 531, 532, 534, 
            535, 536, 537, 539, 
            540, 541, 542, 544, 
            545, 546, 547, 549, 
            550, 551, 552, 553, 
            554, 556, 557, 559, 
            560, 561, 562, 564, 
            565, 566, 568, 569, 
            570, 571, 572, 574, 
            575, 576, 577, 579, 
            580, 581, 582, 583, 
            585, 586, 587, 588, 
            590, 591, 592, 593, 
            594, 596, 597, 598, 
            599, 601, 602, 603, 
            604, 606, 607, 608, 
            609, 611, 612, 613, 
            614, 616, 617, 618, 
            620, 621, 622, 623, 
            625, 626, 627, 628, 
            629, 631, 632, 633, 
            634, 636, 637, 638, 
            639, 641, 642, 643, 
            644, 646, 647, 648, 
            649, 651, 652, 653, 
            654, 656, 657, 658, 
            659, 660, 662, 663, 
            664, 665, 667, 668, 
            669, 670, 671, 673, 
            674, 675, 676, 678, 
            679, 680, 682, 683, 
            684, 686, 687, 688, 
            689, 691, 692, 693, 
            694, 697, 698, 699, 
            702, 703, 704, 707, 
            708, 709, 710, 712, 
            713, 714, 717, 718, 
            719, 720, 721, 724, 
            725, 726, 728, 729, 
            730, 734, 735, 736, 
            738, 739, 740, 742, 
            743, 744, 747, 748, 
            749, 751, 752, 753, 
            755, 756, 757, 759, 
            760, 761, 763, 764, 
            765, 767, 768, 769, 
            771, 772, 773, 775, 
            776, 777, 779, 780, 
            781, 782, 784, 785, 
            786, 788, 789, 790, 
            791, 793, 794, 795, 
            797, 798, 799, 800, 
            802, 803, 804, 807, 
            813, 814, 815, 816, 
            818, 822, 823, 824, 
            825, 830, 831, 832, 
            834, 835, 836, 837, 
            839, 840, 841, 842, 
            844, 845, 846, 848, 
            849, 850, 852, 853, 
            855, 856, 858, 859, 
            860, 862, 863, 864, 
            866, 867, 868, 870, 
            871, 872, 874, 875, 
            876, 877, 879, 880, 
            881, 883, 884, 886, 
            888, 889, 891, 892, 
            893, 895, 899, 900, 
            902, 903, 905, 906, 
            908, 909, 911, 912, 
            914, 915, 917, 918, 
            920, 921, 923, 925, 
            927, 929, 931, 932, 
            934, 936, 938, 940, 
            942, 944, 946, 948, 
            950, 952, 953, 955, 
            956, 958, 959, 961, 
            962, 963, 965, 966, 
            968, 969, 971, 972, 
            974, 975, 977, 978, 
            979, 981, 982, 983, 
            987, 988, 991, 992, 
            994, 995, 996, 998, 
            1000, 1001, 1002, 1003, 
            1005, 1007, 1008, 1009, 
            1011, 1013, 1014, 1016, 
            1017, 1019, 1020, 1022, 
            1023, 1024, 1025, 1028, 
            1029, 1032, 1033, 1035, 
            1036, 1038, 1040, 1041, 
            1043, 1045, 1046, 1049, 
            1050, 1052, 1053, 1055, 
            1056, 1059, 1060, 1063, 
            1064, 1067, 1068, 1070, 
            1071, 1073, 1074, 1076, 
            1077, 1079, 1080, 1082, 
            1083, 1087, 1088, 1090, 
            295, 296, 338, 1551, 
            1552, 1554, 1556, 1559, 
            1561, 1563, 1565, 1567, 
            1568, 1570, 1572, 1574, 
            1576, 1578, 1580, 1581, 
            1583, 1585, 1587, 1589, 
            1591, 1593, 1595, 1597, 
            1599, 1601, 1603, 1605, 
            1607, 1609, 1611, 1613, 
            1614, 1617, 1618, 1621, 
            1622, 1625, 1626, 1629, 
            1630, 1634, 1638, 1639, 
            1642, 1643, 1645, 1646, 
            1651, 1652, 1657, 1658, 
            1662, 1664, 1666, 1669, 
            1672, 1676, 1674, 1677, 
            1680, 1681, 1684, 1685, 
            1689, 1690, 1694, 1698, 
            1704, 1706, 1709, 1712, 1633) 
       AND DataSourceActivityLog.Id = (SELECT DataSourceActivityLog.Id 
               FROM DataSourceActivityLog 
               WHERE DataSourceActivityLog.DataSourceId = DataSource.Id 
                 AND (DataSourceActivityLog.Description = 'data_entry_ready') 
               ORDER BY TIMESTAMP DESC 
               LIMIT 1) 
       AND (DataSource.Status = '103') 
       AND Workflow.Id = 14 
       AND DataSourceActivityLog.`DataSourceId` = DataSource.`Id` 
       AND DataSource.`WorkflowId` = Workflow.`Id` 
       AND DataSource.IsDeleted = 0) AS WrappedData 
ORDER BY WrappedData.`Timestamp` ASC 
LIMIT 0, 1

來源

2011-06-13 StackOverflowNewbie

查詢就好了。 – Femaref 2011-06-13 22:54:29

哈哈！和表defs也將得心應手:) – Bohemian 2011-06-13 22:57:44

@Femaref - 請參閱編輯。 – StackOverflowNewbie 2011-06-13 23:00:07

首先它似乎很奇怪，這是一個大的子查詢。爲什麼你不能做到這一點：

SELECT DataSource.Id, 
       DataSourceActivityLog.Description, 
       DataSourceActivityLog.UserId, 
       DataSource.Status AS StatusCode, 
       (CASE 
        WHEN User.Name IS NULL THEN 'System' 
        ELSE User.Name 
       END)    AS `Username`, 
       ReadyLog.`Timestamp` AS `Received`, 
       DataSourceActivityLog.`Timestamp` 
     FROM DataSource 
       LEFT JOIN DataSourceActivityLog AS ReadyLog 
       ON ((ReadyLog.DataSourceId = DataSource.Id 
         AND ReadyLog.Description = 'ready') 
         OR (ReadyLog.DataSourceId = DataSource.RootId 
          AND ReadyLog.Description = 'ready')), 
       DataSourceActivityLog 
       LEFT JOIN USER 
       ON USER.Id = DataSourceActivityLog.UserId, 
       Workflow 
     WHERE DataSource.Id IN (...) 
       AND DataSourceActivityLog.Id = (SELECT DataSourceActivityLog.Id 
               FROM DataSourceActivityLog 
               WHERE DataSourceActivityLog.DataSourceId = DataSource.Id 
                 AND (DataSourceActivityLog.Description = 'data_entry_ready') 
               ORDER BY TIMESTAMP DESC 
               LIMIT 1) 
       AND (DataSource.Status = '103') 
       AND Workflow.Id = 14 
       AND DataSourceActivityLog.`DataSourceId` = DataSource.`Id` 
       AND DataSource.`WorkflowId` = Workflow.`Id` 
       AND DataSource.IsDeleted = 0 
ORDER BY DataSourceActivityLog.`Timestamp` ASC 
LIMIT 0, 1

我懷疑，但可能是錯誤的，那WrappedData衍生的ORDER BY是低效的，因爲它不能使用任何索引，並且必須等待整個查詢完成在排序之前。

下，似乎有些where子句應該進入加入這樣的：

SELECT DataSource.Id, 
       DataSourceActivityLog.Description, 
       DataSourceActivityLog.UserId, 
       DataSource.Status AS StatusCode, 
       (CASE 
        WHEN User.Name IS NULL THEN 'System' 
        ELSE User.Name 
       END)    AS `Username`, 
       ReadyLog.`Timestamp` AS `Received`, 
       DataSourceActivityLog.`Timestamp` 
     FROM DataSource 
       LEFT JOIN DataSourceActivityLog AS ReadyLog 
       ON ((ReadyLog.DataSourceId = DataSource.Id 
         AND ReadyLog.Description = 'ready') 
         OR (ReadyLog.DataSourceId = DataSource.RootId 
          AND ReadyLog.Description = 'ready')), 
       INNER JOIN DataSourceActivityLog ON DataSourceActivityLog.`DataSourceId` = DataSource.`Id` 
               AND DataSourceActivityLog.Id = (SELECT DataSourceActivityLog.Id 
               FROM DataSourceActivityLog 
               WHERE DataSourceActivityLog.DataSourceId = DataSource.Id 
                 AND (DataSourceActivityLog.Description = 'data_entry_ready') 
               ORDER BY TIMESTAMP DESC 
               LIMIT 1) 
       LEFT JOIN USER 
       ON USER.Id = DataSourceActivityLog.UserId 
       INNER JOIN Workflow ON DataSource.`WorkflowId` = Workflow.`Id` 
     WHERE DataSource.Id IN (...) 
       AND (DataSource.Status = '103') 
       AND Workflow.Id = 14 
       AND DataSource.IsDeleted = 0 
ORDER BY DataSourceActivityLog.`Timestamp` ASC 
LIMIT 0, 1

此外，別名DataSourceActivityLog AS ReadyLog看起來像它返回不少行。這應該是INNER JOIN而不是LEFT JOIN？很難根據您提供的內容來判斷。

最後，DataSource.Id IN (...)是如此之久，它可能有益於你把這些ID放到一個查找表中，你可以通過一個連接來引用，而不是把它們全部放在where子句中。

我知道這對EXPLAIN沒有幫助，但說實話，我認爲在這種情況下它不會給你太多的幫助。

來源

2011-06-14 04:19:14 NullRef

我會嘗試以下操作，首先將IN子句的ID放在臨時表（TempIds）中;如果您可以確定表Workflow中存在Id=14，那麼您可以刪除INNER JOIN至Workflow表，並在WHERE子句中保留DataSource.WorkflowId = 14的簡單條件;然後更改聯接的順序，以便首先評估INNER JOIN，然後再評估LEFT JOIN;簡化第一LEFT JOIN表達和移動不變的條件ReadyLog.Description = 'ready'出OR的：

SELECT DataSource.Id, 
    DataSourceActivityLog.Description, 
    DataSourceActivityLog.UserId, 
    DataSource.Status AS StatusCode, 
    (CASE 
     WHEN User.Name IS NULL THEN 'System' 
     ELSE User.Name 
    END)    AS `Username`, 
    ReadyLog.`Timestamp` AS `Received`, 
    DataSourceActivityLog.`Timestamp` 
FROM 
    TempIds INNER JOIN 
    DataSource ON TempIds.Id = DataSource.Id INNER JOIN 
    DataSourceActivityLog ON DataSourceActivityLog.DataSourceId = DataSource.Id 
     AND DataSourceActivityLog.Id = (
      SELECT DataSourceActivityLog.Id 
      FROM DataSourceActivityLog 
      WHERE DataSourceActivityLog.Description = 'data_entry_ready' 
       AND DataSourceActivityLog.DataSourceId = DataSource.Id 
      ORDER BY TIMESTAMP DESC 
      LIMIT 1) LEFT JOIN 
    DataSourceActivityLog AS ReadyLog ON ReadyLog.Description = 'ready' 
     AND (ReadyLog.DataSourceId = DataSource.Id 
      OR ReadyLog.DataSourceId = DataSource.RootId) LEFT JOIN 
    USER ON USER.Id = DataSourceActivityLog.UserId 
WHERE 
    DataSource.Status = '103' 
    AND DataSource.WorkflowId = 14 
    AND DataSource.IsDeleted = 0 
ORDER BY DataSourceActivityLog.`Timestamp` ASC 
LIMIT 0, 1;

最後，你應該考慮增加以下索引DataSourceActivityLog表：

(Description ASC, DataSourceId ASC)

來源

2011-06-14 05:10:27 Xint0

回答

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