MYSQL不同條件

Question

你好
我有如下的MySQL表列：COND 額定值1，rating2，價格，覈定

是否有可能選擇的結果是這樣的：

select 
average rating1 + rating2 as total_rating, 
average rating1 as rating1, 
average rating2 as rating2, 
average price if cond = '1' as price_used 
average price if cond = '2' as price_new 
where approved = '1' 

到目前爲止，我有：

SELECT 
(AVG(t.rating1) + AVG(t.rating2))/2 AS total_rating 
AVG(t.rating1) AS rating1, 
AVG(t.rating2) AS rating2, 
---- price statements?? ---- 
FROM t 
WHERE 1=1 
AND t.approved = '1' 

非常感謝，並原諒我的英語

Answer 1

標準SQL，可以跨越 「所有」 主要DBMS：

select (avg(t.rating1) + avg(t.rating2))/2 as total_rating 
     ,avg(t.rating1) as rating1 
     ,avg(t.rating2) as rating2 
     ,avg(case when cond = '1' then price end) as price_used 
     ,avg(case when cond = '2' then price end) as price_new 
    from t 
where t.approved = '1' 

Answer 2

試試這個：

SELECT (AVG(t.rating1) + AVG(t.rating2))/2 AS total_rating, 
       AVG(t.rating1) AS rating1, 
       AVG(t.rating2) AS rating2, 
       AVG(IF(cond='1', price, NULL)) price_used, 
       AVG(IF(cond='2', price, NULL)) price_new 
FROM t 
WHERE 1=1 
AND t.approved = '1' 

編輯：更新了查詢以獲得期望的結果。

Answer 3

我不認爲If語句的平均值會起作用。但是這裏是IF的語法。

IF（條件，value_to_display_if_true，value_to_display_if_false）

因此，舉例來說，IF（1 = 1， '真'， '假'）總是因爲1確實= 1顯示 '真' 此列。