選擇基於計數

Question

的結果不同的數據我有一個非常簡單的查詢是這樣的：

SELECT users.id, COUNT(others.id) as c 
FROM users JOIN other ON users.id=others.user_id 
GROUP BY users.id 

我想這樣做是''時c=0替換c數量。

例如，而不是像

# I have this 
1, 0 
2, 1 

# I want c=0 replaced with '' 
1, '' 
2, 1 

我怎麼能在MySQL做這行？

Answer 1

試試這個：

SELECT users.id, IF(COUNT(others.id) = 0, '', COUNT(others.id)) as c 
FROM users JOIN other ON users.id=others.user_id 
GROUP BY users.id 

Answer 2

使用CASE or IF

SELECT t.id, CASE t.c = 0 THEN '' ELSE t.c FROM (
    SELECT users.id as id, COUNT(others.id) as c 
    FROM users JOIN other ON users.id=others.user_id 
    GROUP BY users.id 
) as t 

Answer 3

你可以試試這個：

SELECT users.id, IF(COUNT(others.id) > 0, COUNT(others.id), "''") as c 
FROM users JOIN other ON users.id=others.user_id 
GROUP BY users.id 

或者有COALESCE，但如果不能與0的結果工作

「‘’」（內2個qoutes 2個單引號）會給你

1「」而不是

1，