的MySQL到PostgreSQL查詢別名GROUP BY

Question

我有一個表，看起來像這樣

 
id | number 
--------------- 
1  56721 
2  56722 
3  43981 
4  43982 
5  43983 
6  43984 

我的MySQL查詢看起來是這樣的：

SELECT CASE substr(number,1,2) WHEN '56' then 'class1' WHEN '43' then 'class2' else 'other' END as class, 
     CASE substr(number,3,2) WHEN '72' then 'subclass1', WHEN '98' then 'subclass2' ELSE 'other' END as subclass, count(id) as ct 
FROM table GROUP BY class, subclass HAVING class!='other' AND subclass!='other' 
ORDER BY class ASC, subclass DESC; 

，這是什麼相應的PostgreSQL的查詢？

Answer 1

爲了使它更清晰，把它包裝上的子查詢：

SELECT class, subclass 
FROM 
    (
     SELECT CASE substr(number,1,2) WHEN '56' then 'class1' WHEN '43' then 'class2' else 'other' END as class, 
       CASE substr(number,3,2) WHEN '72' then 'subclass1', WHEN '98' then 'subclass2' ELSE 'other' END as subclass 
     FROM table 
    ) x 
GROUP BY class, subclass 
HAVING class != 'other' AND subclass != other 
ORDER BY class ASC, subclass DESC; 

Answer 2

如果number數字（這對我來說很有意義）實際存儲，那麼你需要處理的類型轉換。 MySQL支持substr()的數值，但不是Postgres的：

SELECT class, subclass, count(*) 
FROM (SELECT (CASE substr(numstr,1,2) WHEN '56' then 'class1' 
             WHEN '43' then 'class2' 
             else 'other' 
       END) as class, 
       (CASE substr(numstr,3,2) WHEN '72' then 'subclass1' 
             WHEN '98' then 'subclass2' 
             ELSE 'other' 
       END) as subclass 
     FROM (select t.*, cast(number as varchar(255)) as numstr 
       from table t 
      ) t 
    ) t 
WHERE class <> 'other' AND subclass <> 'other' 
GROUP BY class, subclass 
ORDER BY class ASC, subclass DESC; 

我也改了比較having子句中subclass <> 'other'。沒有名爲other的專欄，所以我認爲你的意思是價值。