面试遇到的一些SQL语句题目

最近忙着找工作，也面试了不少公司，做了不少笔试题目，现在把遇到的一些SQL 题目贴出来：

1.把以下表
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
1992 4 2.4
查成这样一个结果
year m1 m2 m3 m4
1991 1.1 1.2 1.3 1.4
1992 2.1 2.2 2.3 2.4

SELECT
	YEAR,
	(
		SELECT
			amount
		FROM
			yearr yearr2
		WHERE
			MONTH = 1
		AND yearr. YEAR = yearr2. YEAR
	) AS m1,
	(
		SELECT
			amount
		FROM
			yearr yearr2
		WHERE
			MONTH = 2
		AND yearr. YEAR = yearr2. YEAR
	) AS m2,
	(
		SELECT
			amount
		FROM
			yearr yearr2
		WHERE
			MONTH = 3
		AND yearr. YEAR = yearr2. YEAR
	) AS m3,
	(
		SELECT
			amount
		FROM
			yearr yearr2
		WHERE
			MONTH = 4
		AND yearr. YEAR = yearr2. YEAR
	) AS m4
FROM
	yearr
GROUP BY
	YEAR;