PostgreSQL9.5新特性width_bucket
postgres=# select width_bucket(-1, 0.0, 5.0, 5);
width_bucket
--------------
0
(1 row)
postgres=# select width_bucket(5.0, 0.0, 5.0, 5);
width_bucket
--------------
6
(1 row)
postgres=# select width_bucket(-0.0000001, 0.0, 5.0, 5);
width_bucket
--------------
0
(1 row)
postgres=# select width_bucket(5.1, 0.0, 5.0, 5);
width_bucket
--------------
6
(1 row)
在边界内：
postgres=# select width_bucket(0, 0.0, 5.0, 5);
width_bucket
--------------
1
(1 row)
postgres=# select width_bucket(1, 0.0, 5.0, 5);
width_bucket
--------------
2
(1 row)
postgres=# select width_bucket(1.9, 0.0, 5.0, 5);
width_bucket
--------------
2
(1 row)
postgres=# select width_bucket(1.9999999, 0.0, 5.0, 5);
width_bucket
--------------
2
(1 row)
postgres=# select width_bucket(2, 0.0, 5.0, 5);
width_bucket
--------------
3
(1 row)
postgres=# select width_bucket(4.9999, 0.0, 5.0, 5);
width_bucket
--------------
5
(1 row)
直接使用数组代表边界：
注意参数类型必须一致。
postgres=# select width_bucket(now(), array["yesterday", "today", "tomorrow"]::timestamptz[]);
width_bucket
--------------
2
(1 row)
postgres=# select width_bucket(now(), array["yesterday", "today", "tomorrow"]::timestamp[]);
ERROR: function width_bucket(timestamp with time zone, timestamp without time zone[]) does not exist
LINE 1: select width_bucket(now(), array["yesterday", "today", "tomo...
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.
postgres=# select width_bucket(1,"{0,1,100,200,300}"::int[]);
width_bucket
--------------
2
(1 row)
边界表示如下，所以1落在第二个bucket。
[0,1)
[1,100)
[100,200)
[200,300)
[参考]
1. http://www.postgresql.org/docs/devel/static/functions-math.html#FUNCTIONS-MATH-FUNC-TABLE
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