关于mysql：UNION ALL返回多个结果

UNION ALL is returning multiple results

本问题已经有最佳答案，请猛点这里访问。

此查询返回多个结果。在底部，您可以看到每个ID号中有两个。如何区分仍然有25个唯一值记录的记录？

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SELECT *
FROM(
SELECT
DISTINCT cards.id, cards.name, cards.created_at, cards.updated_at
FROM cards
INNER JOIN card_process
ON card_process.card_id = cards.id
INNER JOIN processes
ON processes.id = card_process.process_id
INNER JOIN category_process
ON category_process.process_id = processes.id
INNER JOIN categories
ON categories.id = category_process.category_id
INNER JOIN series
ON series.id = categories.serie_id
INNER JOIN serie_user
ON serie_user.serie_id = series.id
AND `cards`.`type` NOT IN ('', 'libraries')
AND NOT `cards`.`deleted`
AND NOT `categories`.`deleted`
AND NOT `series`.`deleted`
AND `cards`.`type` IN ('forms')
AND `series`.`id` IN (124,235,126,126,201,236,207,207,207,207,247,234,131,131,221,225,225,222)
UNION ALL
SELECT
DISTINCT cards.id, cards.name, cards.created_at, cards.updated_at
FROM cards
WHERE `cards`.`account_user_id`='9'
AND NOT `cards`.`deleted`
AND `cards`.`type` IN ('forms')
) AS qry
ORDER BY `updated_at` ASC
LIMIT 0, 25

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相关讨论

不了解任何关于模式或数据形状的信息，您可以通过简化查询来获得所需的内容。假设大致符合标准的SQL方言

您不需要随附的select。全选(unioned select表达式)接受order by，该order by应用于整个全选。
在UNION中的单个select语句中不需要distinct关键字：UNION本身消除了重复行。

请在编写一个长而复杂的查询时，花些时间对其进行格式化，以便下一个必须理解它的SOD(几年后可能是您)能够轻松地完成这项工作。

这就相当于：

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SELECT cards.id ,
cards.name ,
cards.created_at ,
cards.updated_at
FROM cards
INNER JOIN card_process ON card_process.card_id = cards.id
INNER JOIN processes ON processes.id = card_process.process_id
INNER JOIN category_process ON category_process.process_id = processes.id
INNER JOIN categories ON categories.id = category_process.category_id
INNER JOIN series ON series.id = categories.serie_id
INNER JOIN serie_user ON serie_user.serie_id = series.id
AND `cards`.`type` NOT IN ('', 'libraries')
AND NOT `cards`.`deleted`
AND NOT `categories`.`deleted`
AND NOT `series`.`deleted`
AND `cards`.`type` IN ('forms')
AND `series`.`id` IN (124,235,126,126,201,236,207,207,207,207,247,234,131,131,221,225,225,222)
UNION
SELECT cards.id ,
cards.name ,
cards.created_at ,
cards.updated_at
FROM cards
WHERE `cards`.`account_user_id`='9'
AND NOT `cards`.`deleted`
AND `cards`.`type` IN ('forms')
ORDER BY `updated_at` ASC
LIMIT 0, 25

如果MySQL不允许对完全选择进行限制，那么您可能需要包含select语句。

另外，您可能会注意到您的连接条件几乎肯定是不正确的。在第一个选择中，表serie_user的连接标准有一系列测试：

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AND `cards`.`type` NOT IN ('', 'libraries')
AND NOT `cards`.`deleted`
AND NOT `categories`.`deleted`
AND NOT `series`.`deleted`
AND `cards`.`type` IN ('forms')
AND `series`.`id` IN (124,235,126,126,201,236,207,207,207,207,247,234,131,131,221,225,225,222)

号

它们只适用于加入来自serie_user的候选行。它们不适用于整个结果集。它们应重构为where子句和相关表的联接标准，从而：

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SELECT cards.id ,
cards.name ,
cards.created_at ,
cards.updated_at
FROM cards
INNER JOIN card_process ON card_process.card_id = cards.id
INNER JOIN processes ON processes.id = card_process.process_id
INNER JOIN category_process ON category_process.process_id = processes.id
INNER JOIN categories ON categories.id = category_process.category_id
AND NOT `categories`.`deleted`
INNER JOIN series ON series.id = categories.serie_id
AND NOT `series`.`deleted`
AND `series`.`id` IN (124,235,126,126,201,236,207,207,207,207,247,234,131,131,221,225,225,222)
INNER JOIN serie_user ON serie_user.serie_id = series.id
WHERE `cards`.`type` NOT IN ('', 'libraries')
AND NOT `cards`.`deleted`
AND `cards`.`type` IN ('forms')
UNION
SELECT cards.id ,
cards.name ,
cards.created_at ,
cards.updated_at
FROM cards
WHERE `cards`.`account_user_id` = '9'
AND NOT `cards`.`deleted`
AND `cards`.`type` IN ('forms')
ORDER BY `updated_at` ASC
LIMIT 0, 25

我要注意的最后一件事是，您加入了一整排结果集中没有使用的表。您所要做的就是从cards表中获取行的子集。这就意味着，如果你简单地摆脱了UNION，所有外来的人都加入进来，简单地问了正确的问题，你可能会过得更好。

这样就完全消除了重复的可能性。

稍加重构就可以做到这一点(不保证我100%正确，但您应该能够了解其中的要点)：

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select c.id ,
c.name ,
c.created_at ,
c.updated_at
from cards c
where not c.deleted
and c.type = 'forms'
and ( c.account_user_id = '9'
OR exists ( select *
from card_process cp
join processes p on p.id = cp.process_id
join category_process cpx on cpx.process_id = p.id
join categories c on c.id = cpx.category_id
and not c.deleted
join series s on s.id = categories.serid_id
and not s.deleted
and series.id IN ( 124 , 235 , 126 , ... )
join serie_user su on su.serid_id = s.id
where cp.card_id = c.card_id
)
)
ORDER BY updated_at
LIMIT 0, 25

。

通常有一个简单的查询隐藏在一个复杂的查询中。