说明：
在统计中用到的MAX聚集函数也可以用sum、min、avg等其他聚集函数替代。用sign和decode来完成比较字段大小来区某个字段
1 select decode(sign(字段1-字段2),-1,字段3,字段4) from dual;
1、使用case进行直方图的统计：
统计工资在各个区间的人数：
1 SELECT SUM(CASE 2 WHEN t.sal < 1000 THEN 3 1 4 ELSE 5 0 6 END) "小于1000", 7 SUM(CASE 8 WHEN t.sal >= 1000 AND t.sal < 2000 THEN 9 1 10 ELSE 11 0 12 END) "1000-2000", 13 SUM(CASE 14 WHEN t.sal >= 2000 AND t.sal < 3000 THEN 15 1 16 ELSE 17 0 18 END) "2000-3000", 19 20 SUM(CASE 21 WHEN t.sal >= 3000 AND t.sal < 4000 THEN 22 1 23 ELSE 24 0 25 END) "3000-4000", 26 SUM(CASE 27 WHEN t.sal >= 4000 THEN 28 1 29 ELSE 30 0 31 END) "大于4000" 32 FROM emp t
结果：
统计在这个区间具体的人：
1 SELECT SUM(CASE 2 WHEN t.sal < 1000 THEN 3 1 4 ELSE 5 0 6 END) "小于1000", 7 wm_concat(CASE 8 WHEN t.sal < 1000 THEN 9 ename 10 END) "小于1000的具体人", 11 SUM(CASE 12 WHEN t.sal >= 1000 AND t.sal < 2000 THEN 13 1 14 ELSE 15 0 16 END) "1000-2000", 17 wm_concat(CASE 18 WHEN t.sal >= 1000 AND t.sal < 2000 THEN 19 ename 20 END) "1000-2000的具体人", 21 SUM(CASE 22 WHEN t.sal >= 2000 AND t.sal < 3000 THEN 23 1 24 ELSE 25 0 26 END) "2000-3000", 27 wm_concat(CASE 28 WHEN t.sal >= 2000 AND t.sal < 3000 THEN 29 ename 30 END) "2000-3000的具体人", 31 32 SUM(CASE 33 WHEN t.sal >= 3000 AND t.sal < 4000 THEN 34 1 35 ELSE 36 0 37 END) "3000-4000", 38 wm_concat(CASE 39 WHEN t.sal >= 3000 AND t.sal < 4000 THEN 40 ename 41 END) "3000-4000的具体人", 42 SUM(CASE 43 WHEN t.sal >= 4000 THEN 44 1 45 ELSE 46 0 47 END) "大于4000", 48 wm_concat(CASE 49 WHEN t.sal >= 4000 THEN 50 ename 51 END) "大于4000的具体人" 52 FROM emp t
结果：
统计成行列格式：
1 SELECT CASE 2 WHEN t.sal < 1000 THEN 3 '大于2000' 4 WHEN t.sal >= 1000 AND t.sal < 2000 THEN 5 '1000-2000' 6 WHEN t.sal >= 2000 AND t.sal < 3000 THEN 7 '2000-3000' 8 WHEN t.sal >= 3000 AND t.sal < 4000 THEN 9 '3000-4000' 10 WHEN t.sal >= 4000 THEN 11 '大于或等于4000' 12 END "工资分布", 13 COUNT(1) 数量 14 FROM emp t 15 GROUP BY CASE 16 WHEN t.sal < 1000 THEN 17 '大于2000' 18 WHEN t.sal >= 1000 AND t.sal < 2000 THEN 19 '1000-2000' 20 WHEN t.sal >= 2000 AND t.sal < 3000 THEN 21 '2000-3000' 22 WHEN t.sal >= 3000 AND t.sal < 4000 THEN 23 '3000-4000' 24 WHEN t.sal >= 4000 THEN 25 '大于或等于4000' 26 END
也可以将第一组的case进行列转行得到如下的结果：
1 WITH t AS 2 (SELECT SUM(CASE 3 WHEN t.sal < 1000 THEN 4 1 5 ELSE 6 0 7 END) a, 8 9 SUM(CASE 10 WHEN t.sal >= 1000 AND t.sal < 2000 THEN 11 1 12 ELSE 13 0 14 END) b, 15 SUM(CASE 16 WHEN t.sal >= 2000 AND t.sal < 3000 THEN 17 1 18 ELSE 19 0 20 END) c, 21 22 SUM(CASE 23 WHEN t.sal >= 3000 AND t.sal < 4000 THEN 24 1 25 ELSE 26 0 27 END) d, 28 SUM(CASE 29 WHEN t.sal >= 4000 THEN 30 1 31 ELSE 32 0 33 END) e 34 FROM emp t) 35 SELECT '小于1000', 36 t.a 37 FROM t 38 UNION ALL 39 SELECT '1000-2000', 40 t.b 41 FROM t 42 UNION ALL 43 SELECT '2000-3000', 44 t.c 45 FROM t 46 UNION ALL 47 SELECT '3000-4000', 48 t.d 49 FROM t 50 UNION ALL 51 SELECT '大于4000', 52 t.e 53 FROM t
也可以进行列转行：
使用SIGN进行统计：
SIGN函数的说明：sign()函数根据某个值是0、正数还是负数，分别返回0、1、-1