偵測不一致的資料

清理 PostgreSQL 資料庫中的資料

Darryl Reeves, Ph.D.

Industry Assistant Professor, New York University

不一致的資料

某些餐廳稽查規則

score 代表違規次數危害等級圖示

camis    |              name               |  score | ... 
---------+---------------------------------+--------+-----
...      | ...                             | ...    | ...                                   
41659848 | LA BRISA DEL CIBAO              | 20     | ...
40961447 | MESON SEVILLA RESTAURANT        | 50     | ...
50063071 | WA BAR                          | 15     | ...
...      | ...                             | ...    | ...

A（0 到 13）、B（14 到 27）、C（28 以上）
等第情境：
- 初次稽查拿到 A
- 複查可能為 A、B 或 C

¹ https://www1.nyc.gov/assets/doh/downloads/pdf/rii/restaurant-grading-faq.pdf

用 SQL 檢查規則

相依規則可能造成不一致
可用 SQL 編碼規則
A 對應分數 0 到 13

SELECT 
    camis, 
    grade, 
    grade_date, 
    score, 
    inspection_type 
FROM 
    restaurant_inspection 
WHERE 
    grade = 'A' AND 
    score NOT BETWEEN 0 AND 13;

用 SQL 檢查規則

B 對應分數 14 到 27

SELECT 
    camis, 
    grade, 
    grade_date, 
    score, 
    inspection_type 
FROM 
    restaurant_inspection 
WHERE 
    grade = 'B' AND 
    score NOT BETWEEN 14 AND 27;

 camis    | grade | grade_date | score |         inspection_type          
 ---------+-------+------------+-------+----------------------------------
 50034653 | B     | 12/06/2019 | -1    | Cycle Inspection / Re-inspection

用 SQL 檢查規則

SELECT 
    camis, grade, grade_date, score, inspection_type FROM 
    restaurant_inspection 
WHERE 
    (grade = 'A' OR grade = 'B' OR grade = 'C') AND
    inspection_type LIKE '%Reopening%';

 camis    | grade | grade_date | score |                 inspection_type                 | ... 
 ---------+-------+------------+-------+-------------------------------------------------+-----
 ...      | ...   | ...        | ...   | ...                                             | ...
 50005784 | C     | 05/29/2019 | 14    | Cycle Inspection / Reopening Inspection         | ...
 50091190 | C     | 07/12/2019 | 7     | Pre-permit (Operational) / Reopening Inspection | ...
 40395023 | C     | 09/13/2019 | 8     | Cycle Inspection / Reopening Inspection         | ...
 50037770 | C     | 10/26/2018 | 11    | Cycle Inspection / Reopening Inspection         | ...
 50036406 | C     | 07/10/2018 | 20    | Cycle Inspection / Reopening Inspection         | ...
 ...      | ...   | ...        | ...   | ...                                             | ...

¹ https://www1.nyc.gov/assets/doh/downloads/pdf/rii/restaurant-grading-faq.pdf

資料清理洞見

多元作法
需審慎思考
領域知識關鍵
- 哪些值有效
- 為何會重複
- 合適的填補值

一起來練習吧！

清理 PostgreSQL 資料庫中的資料