0

为了简单起见，我需要更新表中的一些行，称为“三”。

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

现在我用我得到的 id 调用更新查询。

有没有机会消除子查询？

编辑（在梅兰妮的评论之后）：

表“一”：

|id|text|

表“二”：

|id|item|page|level|

表“三”：

|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 并且最终的 WHERE 子句将是：

two.item = 1 AND two.level = 1

这与以下内容不同：

two.level = 1 and two.page = 5

我有第一张桌子 - 一些带有 one.id 的文本。我需要更新表三中所有位置高于我的项目（例如 id = 5）的项目。但是这些项目也应该在表二中具有相同的 two.item，其中 two.page = one.id 和 level = 1

我很抱歉描述不佳。

4

2 回答 2

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
于 2013-01-04T22:17:14.850 回答
1

@TheVedge 是有趣的解决方案，但不会产生与您的查询相同的结果

我建议避免与视图重复同一张表，所以稍微更正一下

另一个更正是three2.item=5

我建议在子查询限制 0,1 中使用，所以永远不要返回一个以上的元素

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，您没有对这个查询做同样的事情。

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

通过原始查询，您在 TheVedge 解决方案中选择了特定元素，您正在加入更多数据因此结果取决于您选择的内容

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

显示配置文件显示，在第一次运行您的原始查询时

    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

建议的查询确实

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

于 2013-01-04T23:44:24.573 回答