MySQL：如何在SELECT cluase中使用Multi-SELECT？

Question

我有一个表格，名称​​ aaa ：

year   month amount
1991   1     1.1
1991   2     1.2
1991   3     1.3
1991   4     1.4
1992   1     2.1
1992   2     2.2
1992   3     2.3
1993   4     2.4

我想要一个这样的结果：

year m1   m2   m3   m4
1991 1.1  1.2  1.3  1.4
1992 2.1  2.2  2.3  2.4 

作为一名新手，我无法在数小时内找到出路并进行体验。我尝试了但失败了：

SELECT year,
(SELECT amount FROM aaa WHERE month=1) AS m1,
(SELECT amount FROM aaa WHERE month=2) AS m2,
(SELECT amount FROM aaa WHERE month=3) AS m3,
(SELECT amount FROM aaa WHERE month=4) AS m4
FROM aaa GROUP BY year;  

有人能告诉我吗？或者让我知道在哪里可以找到答案？ Thx提前。

或者这个：

SELECT year,
(SELECT amount FROM aaa m WHERE month=1 AND m.year=aaa.year) AS m1,
(SELECT amount FROM aaa m WHERE month=2 AND m.year=aaa.year) AS m2,
(SELECT amount FROM aaa m WHERE month=3 AND m.year=aaa.year) AS m3,
(SELECT amount FROM aaa m WHERE month=4 AND m.year=aaa.year) AS m4
FROM aaa GROUP BY year;