MySQL - 忽略和如果沒有值

Question

我有一個MySQL查詢獲取高級自定義字段數據的Wordpress。如果其中一個AND行沒有結果，則整個查詢不會提供結果。我想知道是否可以添加一些東西到查詢中，如果沒有AND行的結果，會忽略AND行？

SELECT DISTINCT post_title, 
wp0.post_id as the_post_id, 
wp1.meta_value as _sale_price, 
wp2.meta_value as _regular_price, 
wp3.meta_value as ex_diameter, 
wp4.meta_value as ex_center, 
wp5.meta_value as ex_length, 
wp6.meta_value as ex_alloy, 
wp7.meta_value as ex_butt_1, 
wp8.meta_value as ex_butt_2, 
wp9.meta_value as ex_taper_1, 
wp10.meta_value as ex_taper_2, 
wp11.meta_value as ex_center 


from wp_postmeta as wp0 
INNER JOIN wp_postmeta as wp1 
ON wp1.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp2 
ON wp2.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp3 
ON wp3.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp4 
ON wp4.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp5 
ON wp5.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp6 
ON wp6.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp7 
ON wp7.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp8 
ON wp8.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp9 
ON wp9.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp10 
ON wp10.post_id=wp0.post_id 
INNER JOIN wp_postmeta as wp11 
ON wp11.post_id=wp0.post_id 



INNER JOIN wp_posts as wpp 
ON wp1.post_id=wpp.ID 
WHERE wp1.post_id='39' 
AND wp1.meta_key='_sale_price' 
AND wp2.meta_key='_regular_price' 
AND wp3.meta_key='ex_diameter' 
AND wp4.meta_key='ex_center' 
AND wp5.meta_key='ex_length' 
AND wp6.meta_key='ex_alloy' 
AND wp7.meta_key='ex_butt_1' 
AND wp8.meta_key='ex_butt_2' 
AND wp9.meta_key='ex_taper_1' 
AND wp10.meta_key='ex_taper_2' 
AND wp11.meta_key='ex_center' 

例如; wp3.meta_key ='ex_diameter'可能根本不存在，但是不會得到帶有空白ex_diameter的結果，而是整個結果爲空，並且不返回任何行。

Answer 1

而不是...

INNER JOIN wp_postmeta as wp11 
ON wp11.post_id=wp0.post_id 

WHERE ... 
AND wp11.meta_key='ex_center' 

你可以使用一個「外部聯接」操作，而不是「內部連接」，將狀態從WHERE子句的加入ON條款，並移除任何在從WP11任何列要求非NULL值的條件......

LEFT JOIN wp_postmeta as wp11 
ON wp11.post_id=wp0.post_id 
AND wp11.meta_key='ex_center' 

WHERE ... 

與外連接，如果沒有匹配的行從WP11發現，所有從WP11列將是NULL。 （這就是爲什麼我們需要將條件從WHERE子句移動到ON子句...... WHERE子句中的條件不能滿足NULL ...

對任何可以接受的表格重複相同的模式連續被「失蹤」。

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其實，使用LEFT JOIN，你需要在「駕駛」榜第一，也許希望wp_posts wpp表先在FROM子句和參考wpp.id在外部連接條件我並不認爲需要wp0引用，你可以從wpp.id獲得post_id

SELECT 
    FROM wp_posts wpp 
    LEFT JOIN wp_postmeta wp1 ON wp1.post_id=wpp.id AND wp1.meta_key='_sale_price' 
    LEFT JOIN wp_postmeta wp2 ON wp2.post_id=wpp.id AND wp2.meta_key='...' 
    LEFT JOIN wp_postmeta wp3 ON wp3.post_id=wpp.id AND wp3.meta_key='...' 
    ... 
    LEFT JOIN wp_postmeta wp11 ON wp11.post_id=wpp.id AND wp11.meta_key='ex_center' 
WHERE wpp.id = 39 

我有一種感覺，你剛剛開始體驗使用EAV的歡樂。讓樂趣開始！

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要回答你問...沒有，有沒有辦法讓一個AND condition圍繞這個問題，沒有修改的條件下，通過添加OR條件...

AND (condition OR some_other_condition) 

的MySQL有時在OR條件下表現不佳（性能方面）。