Question

我在mySQL中寻找一种方法，只选择在链接表中具有相应记录的记录。我可能会遭遇隧道视觉，或者遗漏一些简单的东西。

除了上述要求之外，我还有以下查询：

SELECT P.ID, P.NAME, P.SEO_NAME, CI.City, R.Region, C.Country
FROM PROPERTIES P 
LEFT JOIN Cities CI ON P.CITY_ID = CI.CityId
LEFT JOIN Regions R ON P.REGION_ID = R.RegionID
LEFT JOIN Countries C ON P.COUNTRY_ID = C.CountryId 
WHERE APPROVED = '1' AND REGION_ID = '5400' 
ORDER BY RAND() LIMIT 1;

这与我之前的问题有关，在这里：Select rows Having Count in linked table

虽然此链接线程中的答案当时对我有用，但我现在需要上面查询中的附加信息。有什么方法可以限制它，以便只有链接表PROPERTY_PHOTOS PP中的记录（链接ON P.ID = PP.PROPERTY_ID）

提前感谢任何输入。

Answer 1

尝试使用INNER JOIN而不是LEFT JOIN。根据{{3}}的SQL规范：

The INNER JOIN keyword return rows when there is at least one match in both tables.

对于INNER JOIN，这变为：

The LEFT JOIN keyword returns all rows from the left table (table_name1), 
even if there are no matches in the right table (table_name2).

Answer 2

INNER JOIN应该为您执行此操作：

INNER JOIN PROPERTY_PHOTOS PP ON P.ID = PP.PROPERTY_ID

这只会返回两个表中匹配的记录。

Answer 3

SELECT P.ID, P.NAME, P.SEO_NAME, CI.City, R.Region, C.Country
FROM PROPERTIES P 
LEFT JOIN Cities CI ON P.CITY_ID = CI.CityId
LEFT JOIN Regions R ON P.REGION_ID = R.RegionID
LEFT JOIN Countries C ON P.COUNTRY_ID = C.CountryId 
**INNER JOIN PROPERTY_PHOTOS PP ON P.ID = PP.PROPERTY_ID**
WHERE APPROVED = '1' AND REGION_ID = '5400' 
ORDER BY RAND() LIMIT 1;

Answer 4

你需要一个“内部联接”。

Answer 5

还有一个JOIN，但不是LEFT

SELECT ...
FROM PROPERTIES P
...
INNER JOIN PROPERTY_PHOTOS PP ON P.ID = PP.PROPERTY_ID

或只是

SELECT ...
FROM PROPERTIES P
...
JOIN PROPERTY_PHOTOS PP ON P.ID = PP.PROPERTY_ID

因为they are the same。

Answer 6

注意：此查询实际上并不包含照片表，但我会假设您将其作为PP加入

SELECT P.ID, P.NAME, P.SEO_NAME, CI.City, R.Region, C.Country
FROM PROPERTIES P 
LEFT JOIN Cities CI ON P.CITY_ID = CI.CityId
LEFT JOIN Regions R ON P.REGION_ID = R.RegionID
LEFT JOIN Countries C ON P.COUNTRY_ID = C.CountryId 
WHERE APPROVED = '1' AND REGION_ID = '5400' AND PP.PROPERTY_ID IS NOT NULL
ORDER BY RAND() LIMIT 1;

仅选择包含链接记录的记录

6 个答案: