我越来越沮丧,因为我不明白为什么在我的UNION SELECT中缺少一些字段。我阅读了很好的文档,并遵循了最常见的示例,以避免在第一个和第二个SELECT之间获得不同数量的列。
它包括添加NULL列,使两个语句之间的列数达到偶数。
这是我的情况:
$query = "(SELECT GC.GroupNO AS GroupNO,
GC.Name AS Name,
GC.Pax AS Pax,
GC.Start AS Start,
NULL AS custid,
NULL AS firstname,
NULL AS lastname,
NULL AS arrivaldate,
NULL AS hour,
NULL AS pax,
NULL AS cctype,
NULL AS created,
NULL AS sid,
NULL AS ref_source,
NULL AS numnights
FROM LargeGroupHostels, GroupContacts AS GC
WHERE LargeGroupHostels.HostelNumber = %d
AND LargeGroupHostels.Status = %s
AND LargeGroupHostels.GroupNO = GC.GroupNO";
AND GC.Start < %s
ORDER BY LastUpdated DESC LIMIT %d, %d
)UNION(
SELECT
NULL AS GroupNO,
NULL AS Name,
NULL AS Pax,
NULL AS Start,
`custid`,
`firstname`,
`lastname`,
`arrivaldate`,
`hour`,
`pax`,
`cctype`,
`created`,
`sid`,
`ref_source`,
datediff(departdate, arrivaldate) AS numnights
FROM customer_details
WHERE hostelnumber = %d
AND lastupdated = "" AND status != "CANX"
AND booking_type IN ("HOSTEL", "HOSTELPACK")
ORDER BY customer_details.arrivaldate, customer_details.created
LIMIT %d, %d )
';
除了我知道要进行的一些优化和更改之外,我的问题是:-为什么我没有得到这些色谱柱GC.Name,GC.Pax,GC.Start
?如果我反转两个SELECT,则恰好相反,仅考虑GC.Name,GC.Pax,GC.Start
并避免其他列。
对于这种查询,我不太习惯,这是我第一次处理这种查询。我确定我遗漏了一些东西,但我不明白
例如GC.name
,您正在尝试使用UNION Name
。MySQL将它们解释为两个单独的列,因为它无法智能地猜测您的意图(并且可能不应该具有这种能力)。您应该在第一个SELECT语句中为当前没有别名的列名加上别名:
SELECT GC.GroupNO AS GroupNO,
GC.Name AS Name,
GC.Pax AS Pax,
GC.Start AS Start,
在所有其他情况下,您的别名或原始列名称均匹配。
我也同意上面的评论之一,它可能更适合某种JOIN。
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我来说两句