mysql带联接表的多查询并将结果合并到一行

我一直在努力解决这个mysql查询。我想要达到的是，结果变成只有一行。当前，此查询输出的2行和列中的某些字段为空。如何使其仅输出1行，如下所示：

SELECT save AS 'Simpanan', owe AS 'Hutang'
FROM
(
SELECT t.amount AS save, NULL AS owe
FROM trans t JOIN category cat
ON t.category_id = cat.category_id
WHERE cat.category_id = 1
UNION ALL
SELECT NULL AS save, t.amount AS owe
FROM trans t JOIN category cat
ON t.category_id = cat.category_id
WHERE cat.category_id = 2
)

---

看看这里：

如果您确定只有一个结果，请使用子查询

Simpanan    Hutang  
500         200

或：

---

谢谢，这就是我在几个小时前试图达到的目的：）谢谢你的第二个答案。我认为我之前的问题完全没有用<代码>最大值ftw！

SELECT 
   (SELECT t.amount AS save
    FROM trans t JOIN category cat
    ON t.category_id = cat.category_id
    WHERE cat.category_id = 1) AS 'Simpanan',
    (SELECT t.amount AS owe
    FROM trans t JOIN category cat
    ON t.category_id = cat.category_id
    WHERE cat.category_id = 2) AS 'Hutang'

SELECT MAX(save) AS 'Simpanan', MAX(owe) AS 'Hutang'
FROM
(
SELECT t.amount AS save, NULL AS owe
FROM trans t JOIN category cat
ON t.category_id = cat.category_id
WHERE cat.category_id = 1
UNION ALL
SELECT NULL AS save, t.amount AS owe
FROM trans t JOIN category cat
ON t.category_id = cat.category_id
WHERE cat.category_id = 2
)