與動態列

Question

我工作的PostgreSQL 9.1創建表，我有以下表格：

element(element_id int, name varchar, category_id int) 

category(category_id int, name varchar) 

characteristic(characteristic_id int, name varchar, unit varchar) 

category_characteristic(characteristic_id, category_id) 

element_characteristic(element_id, characteristic_id, value) 

試想下表：

elements 
--------------------- 
|id|name |category | 
----------------------- 
|1 |'item 1'|1  | 
|2 |'item 2'|2  | 
|3 |'item 3'|1  | 
--------------------- 

category 
---------------- 
|id|name   | 
|----------------| 
|1 | 'category 1'| 
|2 | 'category 2'| 
---------------- 

characteristic 
-------------------------------- 
|id|name    |unit  | 
-------------------------------- 
|1 |'characteristic 1' | 'unit 1'| 
|2 |'characteristic 2' | 'unit 2'| 
|3 |'characteristic 3' | 'unit 3'| 
|4 |'characteristic 4' | 'unit 4'| 
|5 |'characteristic 5' | 'unit 5'| 
|6 |'characteristic 6' | 'unit 6'| 
-------------------------------- 

category_characteristic 
------------------------------ 
|category_id|characteristic_id | 
|------------------------------ 
|1   |1     | 
|1   |2     | 
|1   |4     | 
|1   |5     | 
|2   |1     | 
|2   |3     | 
|2   |5     | 
------------------------------ 

element_characteristic 
--------------------------------------- 
|id_element|id_characteristic|value  | 
|---------------------------------------| 
|1   |1    |'value a' | 
|1   |2    |'value b' | 
|1   |4    |'value c' | 
|1   |5    |'value d' | 
|2   |1    |'value e' | 
|2   |3    |'value f' | 
|2   |5    |'value g' | 
|3   |1    |'value h' | 
|3   |2    |'value i' | 
|3   |4    |'value j' | 
|3   |5    |'value k' | 
--------------------------------------- 

現在我想以下表格：

category 1 
--------------------------------------------------------------------------- 
|name |characteristic 1|characteristic 2|characteristic 4|characteristic 5| 
| --------------------------------------------------------------------------| 
|item 1 |value a   |value b   |value c   |value d   | 
|item 3 |value h   |value i   |value j   |value k   | 
--------------------------------------------------------------------------- 

category 2 
----------------------------------------------------------- 
|name |characteristic 1|characteristic 3|characteristic 5| 
| ---------------------------------------------------------- 
|item 2 |value e   |value f   |value g   | 
---------------------------------------------------------- 

我想了解什麼是b預測程序走低谷。我已經閱讀了tablefunc文檔，但我無法弄清楚如何動態創建這些過程，因爲類別表中會有N個條目。某種方向將非常感激。

Answer 1

解決方案：

SELECT * 
FROM crosstab (
     'SELECT e.name, c.name, ec.value 
     FROM elements e 
     JOIN element_characteristic ec ON ec.id_element = e.id 
     JOIN characteristic c ON c.id = ec.id_characteristic 
     ORDER BY 1, 2', 

     'SELECT DISTINCT name 
     FROM characteristic 
     ORDER BY 1') 
AS tbl (
    name text 
,characteristic_1 text 
,characteristic_2 text 
,characteristic_3 text 
,characteristic_4 text 
,characteristic_5 text 
,characteristic_6 text 
); 

測試設置：

CREATE TEMP TABLE elements(id int, name text, category int); 
INSERT INTO elements VALUES 
(1, 'item 1', 1) 
,(2, 'item 2', 2) 
,(3, 'item 3', 1); 

CREATE TEMP TABLE element_characteristic(id_element int 
             ,id_characteristic int, value text); 
INSERT INTO element_characteristic VALUES 
(1,1,'value a') 
,(1,2,'value b') 
,(1,4,'value c') 
,(1,5,'value d') 
,(2,1,'value e') 
,(2,3,'value f') 
,(2,5,'value g') 
,(3,1,'value h') 
,(3,2,'value i') 
,(3,4,'value j') 
,(3,5,'value k'); 

CREATE TEMP TABLE characteristic (id int, name text, unit text); 
INSERT INTO characteristic VALUES 
(1,'characteristic 1', 'unit 1') 
,(2,'characteristic 2', 'unit 2') 
,(3,'characteristic 3', 'unit 3') 
,(4,'characteristic 4', 'unit 4') 
,(5,'characteristic 5', 'unit 5') 
,(6,'characteristic 6', 'unit 6'); 

結果：

name | characteristic 1 | characteristic_2 | characteristic_3 | characteristic_4 | characteristic_5 | characteristic_6 
-------|------------------|------------------|------------------|------------------|------------------|---------------- 
item 1 | value a   | value b   | <NULL>   | value c   | value d   | <NULL> 
item 2 | value e   | <NULL>   | value f   | <NULL>   | value g   | <NULL> 
item 3 | value h   | value i   | <NULL>   | value j   | value k   | <NULL> 

你的問題的解決方案是使用crosstab()變異與兩個參數。

查詢輸出所有項目。將第一個查詢添加WHERE子句以篩選類別。

第二個參數（另一查詢字符串）產生輸出列的列表中，使得在數據查詢NULL值（第一個參數）被正確地分配。

檢查的手冊tablefunc extension，特別crosstab(text, text)：

我已經發布關於tablefunc模塊的crosstab()功能一對夫婦的答案。 This search會給你更多的例子和解釋。