oracle 挑选出现次数最多的前5条数据

oracle 选取出现次数最多的前5条数据
SELECT
	*
FROM
	(
		SELECT
			PROJECT_LISTING.MATERIAL,
			COUNT (*) AS "出现次数"
		FROM
			PROJECT_LISTING
		WHERE
			PROJECT_LISTING.MATERIAL IS NOT NULL
		GROUP BY
			PROJECT_LISTING.MATERIAL
		ORDER BY
			COUNT (*) DESC
	) WHERE ROWNUM <= 5

	ORDER BY
			COUNT (*) DESC 是关键排序

COUNT (*) AS "出现次数"  这个可以不写,只是为了看的明白