幫助進行聯合查詢（MySQL）

Question

您好，有人可以看到為什么此查詢失敗嗎？

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

但這一項有效：

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

在第一個中，我不希望表“ ads”中的所有列，查詢僅返回直到... FROM ads A的列。

Answer 1

如果您指定僅選擇A中的字段，那么您將獲得：僅A中的字段。
如果還需要其他表中的字段，則也必須指定它們。

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