帮助连接查询 (MySQL)

发布于 2024-09-12 11:18:35 字数 773 浏览 10 评论 0原文

你好，有人能看出为什么这个查询失败吗？

SELECT  A.idAd, A.ads_in_Cat, A.title, A.currency, A.price, 
A.in_dpt, A.description, A.featured FROM ads A
LEFT JOIN featured F ON F.ad = A.idAd
INNER JOIN dept D ON D.id_dept = A.in_dpt
INNER JOIN sub_cat_ad S ON S.id_sub_cat = A.ads_in_Cat
INNER JOIN cat_ad C ON C.idCat_ad = S.from_cat_ad 
ORDER BY A.featured DESC LIMIT :limit, :offset

但这是有效的：

SELECT *FROM ads 
LEFT JOIN featured ON featured.ad = ads.idAd
INNER JOIN dept ON dept.id_dept = ads.in_dpt
INNER JOIN sub_cat_ad ON id_sub_cat = ads.ads_in_Cat
INNER JOIN cat_ad ON idCat_ad = sub_cat_ad.from_cat_ad
ORDER BY featured DESC LIMIT :limit, :offset

在第一个中，我不需要表“ads”中的所有列，查询仅返回 ...FROM ads A.

原文

Hello can anybody see why this query fails?

SELECT  A.idAd, A.ads_in_Cat, A.title, A.currency, A.price, 
A.in_dpt, A.description, A.featured FROM ads A
LEFT JOIN featured F ON F.ad = A.idAd
INNER JOIN dept D ON D.id_dept = A.in_dpt
INNER JOIN sub_cat_ad S ON S.id_sub_cat = A.ads_in_Cat
INNER JOIN cat_ad C ON C.idCat_ad = S.from_cat_ad 
ORDER BY A.featured DESC LIMIT :limit, :offset

But this one works:

SELECT *FROM ads 
LEFT JOIN featured ON featured.ad = ads.idAd
INNER JOIN dept ON dept.id_dept = ads.in_dpt
INNER JOIN sub_cat_ad ON id_sub_cat = ads.ads_in_Cat
INNER JOIN cat_ad ON idCat_ad = sub_cat_ad.from_cat_ad
ORDER BY featured DESC LIMIT :limit, :offset

In the first one, I don't want all columns from the table "ads", the query returns only columns till ...FROM ads A.

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战皆罪 2024-09-19 11:18:35

如果您指定仅从 A 选择字段，您将得到：仅从 A 中选择字段。
如果您也需要其他表中的字段，则也必须指定它们。

SELECT
  A.idAd, A.ads_in_Cat, A.title, A.currency, A.price, A.in_dpt, A.description, A.featured,
  F.*,
  D.*,
  S.*,
  C.*
FROM ads A
LEFT JOIN featured F ON F.ad = A.idAd
INNER JOIN dept D ON D.id_dept = A.in_dpt
INNER JOIN sub_cat_ad S ON S.id_sub_cat = A.ads_in_Cat
INNER JOIN cat_ad C ON C.idCat_ad = S.from_cat_ad 
ORDER BY A.featured DESC LIMIT :limit, :offset

If you specify to only select fields from A that's what you get: Only fields from A.
If you want fields from other tables too you have to specify them as well.

SELECT
  A.idAd, A.ads_in_Cat, A.title, A.currency, A.price, A.in_dpt, A.description, A.featured,
  F.*,
  D.*,
  S.*,
  C.*
FROM ads A
LEFT JOIN featured F ON F.ad = A.idAd
INNER JOIN dept D ON D.id_dept = A.in_dpt
INNER JOIN sub_cat_ad S ON S.id_sub_cat = A.ads_in_Cat
INNER JOIN cat_ad C ON C.idCat_ad = S.from_cat_ad 
ORDER BY A.featured DESC LIMIT :limit, :offset

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