如何显示另一个值而不是NULL？

Question

如何显示“1”而不是NULL？

这里我表：

|policies| 
    |id| |policy| 
     1 abc 
     2 def 

|insurances| 
    |id| |policy_id| |money| 
     1   1  1000 
     2   1  2000 
     3   2  3000 
     4   2  4000 
     5   1  1000 

这里查询：

select sum(money) as cash from insurances i 
INNER JOIN policies p ON p.id = i.policy_id 
WHERE i.policy_id = 3 
Group by i.policy_id 

在这种情况下，当policy_id = 3它显示NULL：

|cash| 
    NULL 

我想表明：

|cash| 
    1 

我也试过，但没有工作：

select sum(money)+1 as cash from insurances i 
INNER JOIN policies p ON p.id = i.policy_id 
WHERE i.policy_id = 3 
Group by i.policy_id; 

Here is the link

Answer 1

SELECT COALESCE(sum(money), 1) as Cash 
FROM (
    SELECT policy_id, money 
    FROM 
    insurances i INNER JOIN policies p 
    ON p.id = i.policy_id 
    WHERE 
    i.policy_id = 1 
) s 

编辑或者你可以用这个小动作尝试：

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