SQL:ORDER BY使用特定列中的子字符串...可能吗？

Question

我有一个数据库,其列是npID,标题,URL和问题.

以下是两年条目的示例:

npID               title               URL               issue
88                 EMR Newsletter      a.com             2010 Third_Quarter
89                 EMR Newsletter      b.com             2010 Second_Quarter
43                 EMR Newsletter      c.com             2010 First_Quarter
47                 EMR Newsletter      d.com             2009 Winter
45                 EMR Newsletter      e.com             2009 Summer
46                 EMR Newsletter      f.com             2009 Spring
44                 EMR Newsletter      g.com             2009 Fall

我想要做的是能够根据"问题"列中的子字符串对结果进行排序.然而,直到2010年,客户使用季节作为标题,并在2010年,他们开始使用季度.在"ORDER BY"中是否有一种方法我可以提供一个单词列表来排序是否/何时在"问题"值中找到它们？

我希望最终结果是这样的:

npID               title               URL               issue
43                 EMR Newsletter      c.com             2010 First_Quarter
89                 EMR Newsletter      b.com             2010 Second_Quarter
88                 EMR Newsletter      a.com             2010 Third_Quarter
47                 EMR Newsletter      d.com             2009 Winter
45                 EMR Newsletter      e.com             2009 Summer
46                 EMR Newsletter      f.com             2009 Spring
44                 EMR Newsletter      g.com             2009 Fall

Answer 1

您可以在其中添加一个CASE声明ORDER BY来完成此操作.更好的途径是更改应用程序和表,以便在您有开发时间时将这些相关数据实际存储在它所属的列中.

ORDER BY
    CAST(SUBSTRING(issue, 1, 4) AS INT) DESC,  -- Year
    CASE
        WHEN issue LIKE '%First_Quarter' OR issue LIKE '%Winter' THEN 1
        WHEN issue LIKE '%Second_Quarter' OR issue LIKE '%Spring' THEN 2
        WHEN issue LIKE '%Third_Quarter' OR issue LIKE '%Summer' THEN 3
        WHEN issue LIKE '%Fourth_Quarter' OR issue LIKE '%Fall' THEN 4
    END

订购您想要的季节.您也可以通过调整CASE语句以特定方式(Q1后跟Spring,然后是Q2等)对它们进行排序.

Answer 2

标准SQL

尝试一下CASE声明ORDER BY:

SELECT npID, title, URL, issue
FROM   tbl
ORDER  BY substring(issue, 1, 4) DESC
      ,CASE 
          WHEN substring(issue, 6, 100) IN ('Winter','First_Quarter')  THEN 1
          WHEN substring(issue, 6, 100) IN ('Summer','Second_Quarter') THEN 2
          WHEN substring(issue, 6, 100) IN ('Spring','Third_Quarter')  THEN 3
          WHEN substring(issue, 6, 100) IN ('Fall',  'Fourth Quarter') THEN 4
          ELSE 5 
       END;

不要问,为什么Winter -> Summer -> Spring- 这是客户想要的!:)

优化性能

"简单"CASE应该表现得更好,因为表达式只被评估一次.
而right(issue, -5)就相当于substring(issue, 6, 100),但有点快:

SELECT npid, title, url, issue
FROM   tbl
ORDER  BY left(issue, 4) DESC
      ,CASE right(issue, -5)
          WHEN 'Winter'         THEN 1
          WHEN 'First_Quarter'  THEN 1
          WHEN 'Summer'         THEN 2
          WHEN 'Second_Quarter' THEN 2
          WHEN 'Spring'         THEN 3
          WHEN 'Third_Quarter'  THEN 3
          WHEN 'Fall'           THEN 4
          WHEN 'Fourth Quarter' THEN 4
          ELSE 5 
       END;

left()并right()已添加PostgreSQL 9.1.诀窍right()是使用负数来修剪左边的常数字符.

语法变体

这些是等效的(对于<= 100个字符的字符串):

SELECT substring(issue from 6 for 100) AS substring1
      ,substring(issue, 6, 100)        AS substring2
      ,substring(issue, 6)             AS substring3
      ,substr(issue, 6, 100)           AS substr1
      ,substr(issue, 6)                AS substr2
      ,right(issue, -5)                AS right0
FROM tbl

- > sqlfiddle