Question

道歉，如果这是一个愚蠢的问题，但我无法理解这一点。我想只选择带冒号的值（如果存在），该值为“county”。但是，我不确定我是否正确地采取了这种方式？任何帮助将不胜感激。

SELECT pe.personname AS "Person Name", pe.street||','||pe.town||','||
    IF NOT EXISTS(SELECT pe.county FROM persons pe WHERE pe.county = '')
    THEN pe.county||','|| 
    ELSE
    END IF
 pe.postcode as "Persons Address"
 FROM persons pe

更新版本，如果没有县，则会输出多个逗号。

SELECT personname as "Person Name"
street||','||town||
   CASE county
   WHEN '' THEN ''
   ELSE ','||county
   END
||','||postcode as "Person Address"
from Suppliers;

Answer 1

我已经为此而去了缺少关键字错误： -

 SELECT personname AS "Person Name", 
   street || ',' || town || ',' ||
     CASE WHEN county > ''
     THEN county || ','
     ELSE ''
     END 
   || postcode AS "Person Address"
 FROM Persons

Answer 2

我认为你的意思是逗号。

SELECT pe.personname AS "Person Name", pe.street||','||pe.town||
  IF pe.county <> ''
  THEN ','||pe.county
  ELSE ''
  END IF
pe.postcode as "Persons Address"
FROM persons pe

它可能更干净，（你可能不得不）这样做：

SELECT pe.personname AS "Person Name",
  IF pe.county <> ''
  THEN pe.street||','||pe.town||','||pe.county
  ELSE pe.street||','||pe.town
  END IF
pe.postcode as "Persons Address"
FROM persons pe

Answer 3

如果你想获得两列，一列是人名，第二列是地址部分，我会：

    select pe.personname, pe.street || ',' || pe.town || ',' || 
(case county when not null then (county || ',') else '' end), postcode

使用案例陈述来评估县，如果有一个用'，''来'插入''，

使用IF EXISTS连接SQL select语句

3 个答案: