这是一场长达19小时的恶梦。为什么UPDATE JOIN查询比SELECT JOIN查询慢得多?
我有一个非常大的查询,本质上需要跨几个表连接大型数据集。在进行连接之后,我需要使用select语句中的数据更新原始表。 SELECT语句超快,UPDATE语句超慢。
这是select语句。
SELECT l.col1,
l.col2,
l.col3,
p.personid
FROM table1 p
LEFT JOIN table2 l ON (l.col1 = p.col1)
LEFT JOIN
(SELECT name,
col AS 'col2'
FROM tbl3 f
WHERE f.col LIKE '%-F') pcf ON (pcf.col1 = p.col1)
LEFT JOIN
(SELECT name,
col AS 'col3'
FROM tbl4 f
WHERE f.col LIKE '%-M') pcm ON (pcm.col1 = p.col1)
WHERE p.requestid = '1928'
现在,如果我将EXACT SAME系列的JOIN放入UPDATE上下文中,则查询需要永久。
UPDATE table1 p
LEFT JOIN table2 l ON (l.col1 = p.col1)
LEFT JOIN
(SELECT name,
col AS 'col2'
FROM tbl3 f
WHERE f.col LIKE '%-F') pcf ON (pcf.col1 = p.col1)
LEFT JOIN
(SELECT name,
col AS 'col3'
FROM tbl4 f
WHERE f.col LIKE '%-M') pcm ON (pcm.col1 = p.col1)
SET p.col1 = l.col1,
p.col2 = l.col2,
p.col3 = l.col3
WHERE p.requestid = '1928'
因此......为什么UPDATE JOIN语句比SELECT JOIN语句花费的时间要长得多?时间更长。而且我已经尝试过临时表并且没有工作。
仅供参考,我正在处理50k条记录或更多的表格。
如果你好奇的EXPLAIN的结果,这是当我解释了选择查询会发生什么(尽管显然你不能使用更新的解释?)
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY p ALL NULL NULL NULL NULL 613246 Using where
1 PRIMARY l eq_ref PRIMARY,name_3,name,name_2 PRIMARY 257 drilldev_db.p.lastname 1
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 23435
1 PRIMARY <derived3> ALL NULL NULL NULL NULL 13610
1 PRIMARY <derived4> ALL NULL NULL NULL NULL 13053
1 PRIMARY <derived5> ALL NULL NULL NULL NULL 8273
1 PRIMARY <derived6> ALL NULL NULL NULL NULL 11481
1 PRIMARY <derived7> ALL NULL NULL NULL NULL 6708
1 PRIMARY <derived8> ALL NULL NULL NULL NULL 9588
1 PRIMARY <derived9> ALL NULL NULL NULL NULL 5494
1 PRIMARY <derived10> ALL NULL NULL NULL NULL 6981
1 PRIMARY <derived11> ALL NULL NULL NULL NULL 4107
1 PRIMARY <derived12> ALL NULL NULL NULL NULL 5973
1 PRIMARY <derived13> ALL NULL NULL NULL NULL 3851
1 PRIMARY <derived14> ALL NULL NULL NULL NULL 4935
1 PRIMARY <derived15> ALL NULL NULL NULL NULL 3574
1 PRIMARY <derived16> ALL NULL NULL NULL NULL 5793
1 PRIMARY <derived17> ALL NULL NULL NULL NULL 4706
17 DERIVED f ref year,gender gender 257 364263 Using where; Using temporary; Using filesort
16 DERIVED f ref year,gender gender 257 397322 Using where; Using temporary; Using filesort
15 DERIVED f range year,gender year 4 NULL 54092 Using where; Using temporary; Using filesort
14 DERIVED f range year,gender year 4 NULL 54092 Using where; Using temporary; Using filesort
13 DERIVED f range year,gender year 4 NULL 62494 Using where; Using temporary; Using filesort
12 DERIVED f range year,gender year 4 NULL 62494 Using where; Using temporary; Using filesort
11 DERIVED f range year,gender year 4 NULL 69317 Using where; Using temporary; Using filesort
10 DERIVED f range year,gender year 4 NULL 69317 Using where; Using temporary; Using filesort
9 DERIVED f ref year,gender gender 257 364263 Using where; Using temporary; Using filesort
8 DERIVED f range year,gender year 4 NULL 94949 Using where; Using temporary; Using filesort
7 DERIVED f ref year,gender gender 257 364263 Using where; Using temporary; Using filesort
6 DERIVED f ref year,gender gender 257 397322 Using where; Using temporary; Using filesort
5 DERIVED f ref year,gender gender 257 364263 Using where; Using temporary; Using filesort
4 DERIVED f ref year,gender gender 257 397322 Using where; Using temporary; Using filesort
3 DERIVED f ALL NULL NULL NULL NULL 37045 Using where
2 DERIVED f ALL NULL NULL NULL NULL 37045 Using where
谢谢!
-b
你可以使用命令“explain”并发布输出 – jcho360
你如何测量“select”的“超快速”?所有结果的第一个结果还是时间到了?你可以通过添加'按col1限制1'命令来检查需要多长时间(所有结果都需要为'order by'生成)。 –
为什么你有所有这些JOIN?由于它们是LEFT JOIN,它们不会限制原始表中的匹配行。 – Barmar