CROSSTAB 的使用

使用CROSSTAB实现表的行列翻转，数据的统计

表1： products

id  name
1   Synergistic Marble Gloves
2   Gorgeous Paper Table
3   Awesome Wool Gloves
4   Ergonomic Leather Clock
5   Heavy Duty Iron Knife
6   Heavy Duty Paper Shirt
7   Fantastic Aluminum Table
8   Rustic Paper Plate
9   Rustic Leather Keyboard
10  Intelligent Leather Clock

表2：details

id  product_id  detail
1   10  bad
2   1   bad
3   9   ok
4   4   good
5   2   good
6   5   bad
7   7   bad
8   1   ok
9   8   good
10  8   ok
11  10  ok
12  6   bad
13  7   good
14  8   ok
15  6   bad
16  2   bad
17  9   bad
18  7   good
19  9   ok

sql:

SELECT name, good, ok, bad
FROM crosstab('
  SELECT p.name, d.detail, COUNT(1)
  FROM details AS d JOIN products AS p
    ON d.product_id = p.id
  GROUP BY p.name, d.detail
  ORDER BY p.name, d.detail
  ')
AS ct(name text, bad bigint, good bigint, ok bigint);

结果：

name                                    good    ok      bad
Aerodynamic Concrete Hat                 39     32      31
Awesome Leather Pants                    31     31      29
Durable Granite Computer                 25     35      37
Durable Linen Knife                      45     37      29
Enormous Wooden Plate                    27     38      43
Incredible Bronze Bench                  37     29      47
Mediocre Copper Keyboard                 25     37      26
Mediocre Granite Bag                     33     35      36
Rustic Steel Watch                       24     44      26
Small Granite Lamp                       25     36      31

https://www.postgresql.org/docs/9.5/static/tablefunc.html