mysql 根據某一列進行區間統計

mysql中可以利用elt，interval函數來實現此類需求

mysql> select * from k1;
+------+------+
| id   | yb   |
+------+------+
|    1 |  100 |
|    2 |   11 |
|    3 |    5 |
|    4 |  501 |
|    5 | 1501 |
|    6 |    1 |
+------+------+

現在要進行統計，小於100的，100~500的，500~1000的，1000以上的，這各個區間的id數

利用interval划出4個區間，再利用elt函數將4個區間分別返回一個列名：

mysql> select elt(interval(d.yb,0, 100, 500, 1000), 'less100', '100to500', '500to1000', 'more1000') as yb_level, count(d.id) as cnt
     from k1 d   
     group by yb_level;
+-----------+-----+
| yb_level  | cnt |
+-----------+-----+
| 100to500  |   1 |
| 500to1000 |   1 |
| less100   |   3 |
| more1000  |   1 |
+-----------+-----+
4 rows in set (0.00 sec)

如果需要按從小到大排序的話 可以在列名定義時稍加一個首字符 對各檔區間進行排序

mysql>select elt(interval(d.yb,0, 100, 500, 1000), '1/less100', '2/100to500', '3/500to1000', '4/more1000') as yb_level, count(d.id) as cnt
     from k1 d   
     group by yb_level;
+-------------+-----+
| yb_level    | cnt |
+-------------+-----+
| 1/less100   |   3 |
| 2/100to500  |   1 |
| 3/500to1000 |   1 |
| 4/more1000  |   1 |
+-------------+-----+
4 rows in set (0.00 sec)

附elt函數格式：

ELT(N,str1,str2,str3,...)
如果N= 1，返回str1，如果N= 2，返回str2，等等。如果N小於1或大於參數個數，返回NULL。ELT()是FIELD()反運算。

mysql> select ELT(1, 'ej', 'Heja', 'hej', 'foo');
        -> 'ej'
mysql> select ELT(4, 'ej', 'Heja', 'hej', 'foo');
        -> 'foo'

interval函數格式：        

INTERVAL() Return the index of the argument that is less than the first argument（小於后面的某個參數，就返回這個參數的前一個位置數字）

 INTERVAL(N,N1,N2,N3,...)

Returns 0 if N < N1, 1 if N < N2 and so on or -1 if N is NULL. All arguments are treated as integers. It is required that N1 < N2 < N3 < ... < Nn for this function to work correctly. This is because a binary search is used (very fast).

mysql> SELECT INTERVAL(23, 1, 15, 17, 30, 44, 200); （23小於30，30的位置是4，於是返回3）
        -> 3
mysql> SELECT INTERVAL(10, 1, 10, 100, 1000);
        -> 2
mysql> SELECT INTERVAL(22, 23, 30, 44, 200);
        -> 0