MySQL的投票系統選擇

Question

我有一個投票系統以及表如下所示：

answers 
----------- 
int id 
text content 

results 
----------- 
int id 
int answers_id 

我想選擇這樣我就可以看到答案的數目和響應，即使沒有投票（結果） 。 我想是這樣的：

SELECT 
count(results.answers_id), answers.content 
from answers 
left outer join results 
on answers.id = results.answers_id 
group by results.answers_id 

但它不會與0票（結果）的答案。

Answer 1

這應該做的工作：

SELECT count(results.answer_id), answers.content 
from answers left outer join results on answers.id = results.answer_id 
group by answers.content; 

Answer 2

嘗試

SELECT 
count(result.answers_id) as acount, answers.content 
from answers 
left inner join results 
on answers.id = acount 

Answer 3

使用子查詢

SELECT a.*, 
    (SELECT COUNT(*) 
    FROM results r 
    WHERE a.id = r.answers_id 
    ) 
FROM answers a 

Answer 4

試試這個，對答案的標識分組。

SELECT 
COUNT(results.answers_id) AS NumberOfAnswers, answers.content 
from answers 
left join results 
on answers.id = results.answers_id 
group by answers.id 

要確保你不要有兩行內容相同，那麼group by answers.content

SELECT 
    COUNT(results.answers_id) AS NumberOfAnswers, answers.content 
    from answers 
    left join results 
    on answers.id = results.answers_id 
    group by answers.content 

Answer 5

使用Ifnull，也是你的GROUP BY語句將其更改爲answers.content

SELECT 
IFNULL(count(results.answers_id),0), answers.content 
from answers 
left outer join results 
on answers.id = results.answers_id 
group by answers.content 

Answer 6

我想解決方案是使用IFNULL

SELECT IFNULL(COUNT(r.answers_id), 0), 
     a.content 
FROM answers AS a 
LEFT JOIN results AS r ON a.id = r.answers_id 
GROUP BY r.answers_id