樣式比對

清理 PostgreSQL 資料庫中的資料

Darryl Reeves, Ph.D.

Industry Assistant Professor, New York University

辨識樣式：範例

 camis    |              name               | inspection_date | score | nta  | ... 
 ---------+---------------------------------+-----------------+-------+------+-----
 ...      | ...                             | ...             | ...   | ...  | ...
 41659848 | LA BRISA DEL CIBAO              | 01/30/2018      | 20    | QN26 | ...
 40961447 | MESON SEVILLA RESTAURANT        | 03/19/2019      | 50    | MN15 | ...
 50063071 | WA BAR                          | 05/23/2018      | 15    | MN17 | ...
 50034992 | EMPANADAS MONUMENTAL            | 06/21/2019      | 17    | MN35 | ...
 50095871 | ALPHONSO'S PIZZERIA & TRATTORIA | 01/16/2020      | 10    | MN28 | ...
 41104041 | THE SPARROW TAVERN              | 09/17/2019      | 13    | QN72 | ...
 50016937 | BURGER KING                     | 09/14/2018      | 12    | QN55 | ...
 50066469 | DARBAR'S CHICKEN & RIBS         | 08/07/2017      | 11    | QN55 | ...
 41195691 | F & J PINE RESTAURANT           | 05/02/2019      | 26    | BX49 | ...
 50015706 | EL RINCONCITO DE LOS SABORES    | 12/18/2019      | 20    | QN35 | ...
 ...      | ...                             | ...             | ..    | ...  | ...

¹ https://www1.nyc.gov/site/planning/data-maps/open-data/dwn-nynta.page

辨識樣式：範例

NTA 代碼可用前綴

MN - Manhattan（曼哈頓）
BK - Brooklyn（布魯克林）
BX - Bronx（布朗克斯）
QN - Queens（皇后區）
SI - Staten Island（史坦頓島）

辨識樣式：範例

資料表結果，紅框標示無效的 NTA 代碼

LIKE 運算子

SELECT * FROM restaurant_inspection WHERE nta LIKE 'QN544';

SELECT * FROM restaurant_inspection WHERE nta = 'QN544';

LIKE 運算子

樣式比對字元

%：比對 0 個以上任意字元
_（底線）：比對單一字元

SELECT 
* 
FROM 
restaurant_inspection 
WHERE nta LIKE 'QN%';

SELECT 
* 
FROM 
restaurant_inspection 
WHERE nta LIKE 'QN%' 
AND nta NOT LIKE 'QN__';

Regular expressions（REs）

使用 LIKE 的樣式比對有限
更精確的樣式更實用
Regular Expressions（REs）可進行更具表達力的樣式比對

SIMILAR TO 運算子

提供更多樣式比對功能

SELECT 
  camis, name, inspection_date, score, nta 
FROM 
  restaurant_inspection 
WHERE nta SIMILAR TO 'QN%' AND nta NOT SIMILAR TO 'QN__';

RE 基礎

Metacharacter	用途	RE 範例	範例比對
`\d`	比對數字（0-9）	`\d\d\d`	'345'
`?`	比對前一字元出現 0 或 1 次	`x\d?`	'x5'
`+`	比對前一字元出現 1 次以上	`\d+`	'10'
`*`	比對任意字元 0 次以上	`\d*`	'3081'
`[]`	比對括號內任一字元	`[a-z]`	'f'

搭配 SIMILAR TO 使用 RE

SELECT 
    camis, name, inspection_date, score, nta 
FROM 
    restaurant_inspection 
WHERE nta SIMILAR TO 'QN%' AND nta NOT SIMILAR TO 'QN__';

SELECT 
    camis, name, inspection_date, score, nta 
FROM 
    restaurant_inspection 
WHERE 
    nta NOT SIMILAR TO '[A-Z][A-Z]\d\d';

 camis    |        name        | inspection_date | score | nta  
 ---------+--------------------+-----------------+-------+------
 41659848 | LA BRISA DEL CIBAO | 01/30/2018      | 20    | Q26
 41104041 | THE SPARROW TAVERN | 09/17/2019      | 13    | QN723

一起來練習吧！

清理 PostgreSQL 資料庫中的資料