Question

我需要更新表格中的一些行，为简单起见称为＆＃34;三＆＃34;。

我选择要使用此查询更新的列：

SELECT one.id
FROM one 
    JOIN `two` ON ( one.id = two.page )
    JOIN `three` ON ( one.id = three.item )
WHERE two.level = 1
    AND  two.item = (SELECT item FROM two WHERE page = 5 AND level = 1 ) 
    AND three.position > (SELECT position FROM three WHERE item = 5 ) 
ORDER BY three.position

现在我调用带有id的更新查询。

有没有机会消除子查询？

编辑（在梅兰妮的评论之后）：

表＆＃34;一个＆＃34;：

|id|text|

表＆＃34;两个＆＃34;：

|id|item|page|level|

表＆＃34;三＆＃34;：

|item|position|

所以当我运行查询时

SELECT item FROM two WHERE page = 5 AND level = 1

它将返回f.ex 1，最后的WHERE子句将是：

two.item = 1 AND two.level = 1

与...不同：

two.level = 1 and two.page = 5

我有一张桌子 - 一些带有一些文字的文字。我需要更新表3中比我的项目（f.ex. id = 5）更高位置的所有项目。但是这些项目在表2中也应该具有相同的two.item，其中two.page = one.id和level = 1

我很抱歉描述不好。

Answer 1

您应该能够通过连接替换这些子查询：

SELECT one.id
FROM one 
    JOIN `two2` ON (two2.page = 5 AND two2.level = 1)
    JOIN `two` ON ( one.id = two.page AND two.item = two2.item )
    JOIN `three2` ON ( three.item = 5)
    JOIN `three` ON ( one.id = three.item AND three.position > three2.position)
WHERE two.level = 1
ORDER BY three.position

Answer 2

@TheVedge是一个有趣的解决方案，但不会产生与查询相同的结果

我建议避免使用视图重复同一个表，以便进行一些修正

另一个修正是three2.item = 5

我建议在子查询限制0,1中使用，所以永远不要返回多于一个元素

SELECT one.id
FROM one 
   JOIN `two` AS TWO2 ON (two2.page = 5 AND two2.level = 1)
   JOIN `two` ON ( one.id = two.page AND two.item = two2.item )
   JOIN `three` AS THREE2 ON ( three2.item = 5)
   JOIN `three` ON ( one.id = three.item AND three.position > three2.position)
WHERE two.level = 1
ORDER BY three.position

请记住，您对此查询的处理方式并不相同。

试试这个

 CREATE TABLE `one` (
    `id` INT(10) NULL DEFAULT NULL,
`text` VARCHAR(50) NULL DEFAULT NULL
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

_

CREATE TABLE `three` (
`item` INT(10) NULL DEFAULT NULL,
`position` INT(10) NULL DEFAULT NULL
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

_

CREATE TABLE `two` (
`id` INT(10) NULL DEFAULT NULL,
`item` INT(10) NULL DEFAULT NULL,
`page` INT(10) NULL DEFAULT NULL,
`level` INT(10) NULL DEFAULT NULL
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

_

    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (1, 1, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (3, 3, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (4, 4, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (5, 5, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (6, 6, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (7, 7, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (8, 8, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (9, 9, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (2, 2, 5, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (10, 2, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (11, 1, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (13, 3, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (14, 4, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (15, 5, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (16, 6, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (17, 7, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (18, 8, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (19, 9, 1, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (20, 2, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (21, 1, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (23, 3, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (24, 4, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (25, 5, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (26, 6, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (27, 7, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (28, 8, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (29, 9, 2, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (30, 2, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (31, 1, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (33, 3, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (34, 4, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (35, 5, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (36, 6, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (37, 7, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (38, 8, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (39, 9, 3, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (40, 2, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (41, 1, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (42, 3, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (43, 4, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (44, 5, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (45, 6, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (46, 7, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (47, 8, 4, 1);
    INSERT INTO `two` (`id`, `item`, `page`, `level`) VALUES (48, 9, 4, 1);

-

    INSERT INTO `three` (`item`, `position`) VALUES (1, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (2, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (3, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (4, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (5, 0);
    INSERT INTO `three` (`item`, `position`) VALUES (6, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (7, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (8, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (9, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (10, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (11, 1);
    INSERT INTO `three` (`item`, `position`) VALUES (12, 1);

_

    INSERT INTO `one` (`id`, `text`) VALUES (1, 'A');
    INSERT INTO `one` (`id`, `text`) VALUES (2, 'B');
    INSERT INTO `one` (`id`, `text`) VALUES (3, 'C');
    INSERT INTO `one` (`id`, `text`) VALUES (4, 'D');
    INSERT INTO `one` (`id`, `text`) VALUES (5, 'E');
    INSERT INTO `one` (`id`, `text`) VALUES (6, 'F');
    INSERT INTO `one` (`id`, `text`) VALUES (7, 'G');

_

    SELECT 
  one.id, one.text
 ,two.id,two.item,two.page,two.level
 ,three.item,three.position
FROM one 
    JOIN `two` ON ( one.id = two.page )
   JOIN `three` ON ( one.id = three.item )
WHERE two.level = 1
   AND  two.item = (SELECT item FROM two WHERE page = 5 AND level = 1 limit 0,1 ) 
  AND three.position > (SELECT position FROM three WHERE item = 5 limit 0,1  ) 
 ORDER BY three.position




     SELECT    
 one.id, one.text
 ,two.id,two.item,two.page,two.level
 ,three.item,three.position
FROM one 
    JOIN `two` AS TWO2 ON (two2.page = 5 AND two2.level = 1)
    JOIN `two` ON ( one.id = two.page AND two.item = two2.item )
    JOIN `three` AS THREE2 ON ( three2.item = 5)
    JOIN `three` ON ( one.id = three.item AND three.position > three2.position)
 WHERE two.level = 1
 ORDER BY three.position

使用原始查询，您可以在TheVedge解决方案中选择特定元素，以便加入更多数据所以结果取决于你选择的内容

另一个有用的分析是http://dev.mysql.com/doc/refman/5.0/en/show-profile.html和解释

显示个人资料显示第一次运行时您的原始查询

    Status      Duration
starting    0.000039
checking query cache for query  0.000144
Opening tables  0.000032
System lock 0.000007
Table lock  0.000061
init    0.000054
optimizing  0.000314
statistics  0.000021
preparing   0.000051
Creating tmp table  0.000084
executing   0.000004
Copying to tmp table    0.000063
optimizing  0.000008
statistics  0.000019
preparing   0.000009
executing   0.000004
Sending data    0.000054
optimizing  0.000008
statistics  0.000007
preparing   0.000009
executing   0.000003
Sending data    0.000126
Sorting result  0.000030
Sending data    0.000025
end 0.000004
removing tmp table  0.000011
end 0.000005
query end   0.000004
freeing items   0.000101
storing result in query cache   0.000008
logging slow query  0.000003
cleaning up 0.000006

建议的查询

Status  Duration
starting    0.000036
checking query cache for query  0.000122
Opening tables  0.000030
System lock 0.000008
Table lock  0.000064
init    0.000046
optimizing  0.000028
statistics  0.000026
preparing   0.000072
Creating tmp table  0.000086
executing   0.000005
Copying to tmp table    0.001081
Sorting result  0.000040
Sending data    0.000056
end 0.000005
removing tmp table  0.000010
end 0.000005
query end   0.000004
freeing items   0.000108
storing result in query cache   0.000007
logging slow query  0.000003
cleaning up 0.000005

因此，当您拥有完整数据时，您可以尝试更好地评估两个查询的响应

MySQL查询优化 - 避免子查询

2 个答案: