[英]MySQL SQL Select Query with Multiple Sub-Selects
好,所以這個讓我扯了幾個小時。 我覺得有些明顯的事情我正在忽略。
我有2張桌子, 服務和品牌
service
-------
id
brand
brand
-----
id
brandName
因此,service.brand可以是以下任意一種:
Blank
"Other"
Integer (matches brand.id)
String (matches brand.brandName)
String (Not Blank, Not Other, Not brand.brandName)
我正在嘗試編寫一個查詢,該查詢將從brand表中拉出正確的brandname,如果service.brand的值不在brand.id或brand.brandName中,則顯示其中的內容。
到目前為止,我已經做好了所有工作,但是如果service.brand不為空,不是Other,不在brand.id中,不在brand.brandName中,則不會提高記錄。 (從現在開始,我將其稱為OtherThanOther)。
現在,我的最新嘗試幾乎是正確的,但是OtherThanOther字段卻被拉很多次,例如總記錄為40,OtherThanOther幾乎是同一記錄的20倍。 救命!
我最近的嘗試
select
s.*, b.brandName as bname
from
service s, brand b
where
s.brand = b.brandName
or
s.brand = b.id
or
s.brand = 'Other'
or
s.brand = ''
or
(
s.brand not in (select brandName from brand)
and
s.brand not in (select id from brand)
and
s.brand != 'Other'
and
s.brand != ''
)
樣本表數據
service
-------
1 5
2 Dell
3 SomeRandom
4
5 Other
brand
-----
1 HP
2 Gateway
3 Dell
4 Compaq
5 Toshiba
我的查詢結果
(service.id, service.brand, brand.id, brand.brandName, bname)
-------------------------------------------------------------
1 5 5 Toshiba Toshiba
2 Dell 3 Dell Dell
3 SomeRandom, brand.id, brand.brandName, brand.brandName
3 SomeRandom, brand.id, brand.brandName, brand.brandName
3 SomeRandom, brand.id, brand.brandName, brand.brandName
3 SomeRandom, brand.id, brand.brandName, brand.brandName
3 SomeRandom, brand.id, brand.brandName, brand.brandName
4 '', null, null, null
5 Other, null, null, null
我需要它只拉一次SomeRandom,分組依據將無法工作,因為可能有多個字段的值與SomeRandom相同。 任何幫助深表感謝。
謝謝!
select
s.*,
CASE
WHEN b_id.brandName IS NOT NULL THEN b_id.brandName
WHEN b.brandName IS NOT NULL THEN b.brandName
ELSE s.brand
END as bname
from
service s
LEFT JOIN brand b_id
ON CAST(s.brand AS UNSIGNED) = b_id.id
LEFT JOIN brand b
ON s.brand = b.brandName
您正在使用舊式inner join
:
from service s, brand b
where s.brand = b.brandName or ...
更清晰地寫為:
from service s
inner join brand b on s.brand = b.brandName or ...
在較新的形式中,問題立即突出。 inner join
過濾出不匹配的行。 使用left join
:
from service s
left join brand b on s.brand = b.brandName or ...
現在,即使在brand
表中未找到匹配的行,您也將獲得所有服務。
您應該JOIN
具有多個條件的2個表。 像這樣:
SELECT s.*, b.brandName AS bname
FROM service AS s
INNER JOIN brand AS b
ON s.brand = b.brandName OR
s.brand = b.id OR
s.brand = 'Other' OR
s.brand = '' OR
(s.brand NOT IN (SELECT brandName FROM brand) AND
s.brand NOT IN (SELECT id FROM brand) AND
s.brand != 'Other' AND
s.brand != '')
第一件事-使用JOIN!
select s.*, b.brandName as bname
from service s
LEFT JOIN brand b ON s.brand = b.brandName or s.brand = b.id
然后,您可以添加WHERE NOT s.brand IS NULL
條件-例如WHERE NOT s.brand IS NULL
您的這些情況導致表行彼此相乘的結果:
s.brand = 'Other'
or
s.brand = ''
or
(
s.brand not in (select brandName from brand)
and
s.brand not in (select id from brand)
and
s.brand != 'Other'
and
s.brand != ''
)
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