Mysql如果爲空結果返回默認值

Question

如果初始條目不存在，我試圖讓mysql返回一組基本的值。

這是我已經嘗試：

SELECT 
IFNULL(count(mcr.rating), 1) as rating_count, 
IFNULL(avg(mcr.rating), 5) as rating_average, 
IFNULL(sum(mcr.rating ), 5) as rating_value, 

IFNULL(mck.slug, '-') as rating_slug, 
IFNULL(mck.name, '-') as rating_name, 
IFNULL(mck.criteria_id, '-') as id, 
IFNULL(mck.category, '-') as category 

FROM microstock_criteria_key AS mck 
LEFT JOIN microstock_collective_reviews AS mcr ON mck.criteria_id = mcr.criteria_id 
WHERE mcr.agency_id =5 
GROUP BY mck.criteria_id 
ORDER BY mck.priority ASC 

但我仍然得到：

MySQL返回的查詢結果爲空（即零行）。 （查詢花費 0.0004秒）

當我（如果我沒有理解）會得到我的IFNULL語句設置的默認值。

那麼，如何正確地做到這一點，以返回默認結果，將會是空的結果？

Answer 1

由於您正在使用審覈表的agency_id進行過濾，因此我認爲您需要RIGHT JOIN。

SELECT 
IFNULL(count(mcr.rating), 1) as rating_count, 
IFNULL(avg(mcr.rating), 5) as rating_average, 
IFNULL(sum(mcr.rating ), 5) as rating_value, 

IFNULL(mck.slug, '-') as rating_slug, 
IFNULL(mck.name, '-') as rating_name, 
IFNULL(mck.criteria_id, '-') as id, 
IFNULL(mck.category, '-') as category 

FROM microstock_criteria_key AS mck 
RIGHT JOIN microstock_collective_reviews AS mcr ON mck.criteria_id = mcr.criteria_id 
WHERE mcr.agency_id =5 
GROUP BY mck.criteria_id 
ORDER BY mck.priority ASC