帮助连接查询 (MySQL)

Question

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.

Answer 1

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