在MySQL中選擇不同的行

Question

我遇到了一個問題，我找不出爲什麼會給我帶來麻煩。

我想用DISTINCT語句選擇數據庫中的所有商品，因此每個商品ID都是唯一的。下面是我在截圖的形式登上的Navicat：

Screenshot http://www.dreshar.com/sql.jpg http://www.dreshar.com/sql.jpg

對於任何人誰看不到圖像，這是選擇 - 哪裏是我的錯誤？

SELECT DISTINCT 
guf_offers.id as OfferId, 
guf_offers.validfrom AS OfferValidFrom, 
guf_offers.validtill AS OfferValidTill, 
guf_offers.days AS OfferDays, 
guf_offers.active, 
guf_offers.roomtype1 AS OfferRoomtype1, 
guf_offers.roomprice1 AS OfferRoomprice1, 
guf_countries.caption AS CountryCaption, 
guf_courts.caption AS CourtCaption, 
guf_hotels.caption AS HotelCaption, 
guf_hotels.id AS HotelId, 
guf_hotel_images.image AS HotelImage, 
guf_offer_types.caption AS OffertypeCaption, 
guf_regions.caption AS RegionCaption, 
guf_offers.hoteloncourse AS OfferHotelOnCourse, 
guf_offers.wellnessspa AS OfferWellnessSpa, 
guf_offers.18hole AS Offer18Hole, 
guf_offers.topangebot AS OfferTopangebot 
FROM guf_offers , guf_countries , guf_courts , guf_hotels , guf_hotel_images , guf_offer_types , guf_regions 
WHERE guf_offers.country_id = guf_countries.id AND guf_offers.court_id = guf_courts.id AND guf_offers.hotel_id = guf_hotels.id AND guf_hotel_images.hotel_id = guf_offers.hotel_id AND guf_offers.offer_type_id = guf_offer_types.id AND guf_offers.region_id = guf_regions.id AND guf_offers.active = 1 AND STR_TO_DATE(guf_offers.validtill, '%d.%m.%Y') > STR_TO_DATE('29.04.2013', '%d.%m.%Y') 

Answer 1

DISTINCT返回任何不同的組合列。例如，圖像中OfferId = 89的前兩個實例在HotelImage列中顯示不同的值，因此這些是DISTINCT結果。

Answer 2

如果你想要不同的ID，那麼你可能想要使用group by。查詢看起來是這樣的：

SELECT 
guf_offers.id as OfferId, 
guf_offers.validfrom AS OfferValidFrom, 
guf_offers.validtill AS OfferValidTill, 
guf_offers.days AS OfferDays, 
guf_offers.active, 
guf_offers.roomtype1 AS OfferRoomtype1, 
guf_offers.roomprice1 AS OfferRoomprice1, 
guf_countries.caption AS CountryCaption, 
guf_courts.caption AS CourtCaption, 
guf_hotels.caption AS HotelCaption, 
guf_hotels.id AS HotelId, 
guf_hotel_images.image AS HotelImage, 
guf_offer_types.caption AS OffertypeCaption, 
guf_regions.caption AS RegionCaption, 
guf_offers.hoteloncourse AS OfferHotelOnCourse, 
guf_offers.wellnessspa AS OfferWellnessSpa, 
guf_offers.18hole AS Offer18Hole, 
guf_offers.topangebot AS OfferTopangebot 
FROM guf_offers , guf_countries , guf_courts , guf_hotels , guf_hotel_images , guf_offer_types , guf_regions 
WHERE guf_offers.country_id = guf_countries.id AND guf_offers.court_id = guf_courts.id AND guf_offers.hotel_id = guf_hotels.id AND guf_hotel_images.hotel_id = guf_offers.hotel_id AND guf_offers.offer_type_id = guf_offer_types.id AND guf_offers.region_id = guf_regions.id AND guf_offers.active = 1 AND STR_TO_DATE(guf_offers.validtill, '%d.%m.%Y') > STR_TO_DATE('29.04.2013', '%d.%m.%Y') 
group by guf_offers.id 

其他列來自不同的行任意值。這使用group by的擴展名，其中列可以在select中，即使它們不在聚合函數或group by子句中。

順便說一下，您應該學會使用propoer join語法來練習from子句中的連接。它使查詢更具可讀性和可維護性。