Question

我有一张像这样的表

Col1 | Col2
-----------
a    | d
b    | e
c    | a

现在我想创建一个语句来获得这样的输出：

First| Second
-------------------
a    | Amsterdamm
b    | Berlin
c    | Canada
...

到目前为止，我有这个不起作用的构造

SELECT *
FROM(
    SELECT DISTINCT
        CASE
            when Col1 IS NULL then 'NA' 
            else Col1
        END
        FROM Table1
    UNION
        SELECT DISTINCT
        CASE
            when Col2 IS NULL then 'NA' 
            else Col2
        END
    FROM Table1
    ) AS First
    ,
    (   
    SELECT DISTINCT
        when First= 'a' then 'Amsterdam'
        when First= 'b' then 'Berlin'
        when First= 'c' then 'Canada'
    ) AS Second
;

你可以帮我解决这个问题吗？

抱歉，我必须将我的问题编辑为更具体。

Answer 1

不熟悉DB2 ...我会查找它是否在一秒内有concat function ......而且确实如此。

SELECT First, case when first = 'a' then 
                    concat('This is a ',first)
              case when first = 'b' then 
                    concat('To Be or not to ',first)
              case else  
                    concat('This is a ',first) end  as Second
FROM (
  SELECT coalesce(col1, 'NA') as First 
  FROM Table
  UNION
  SELECT coalesce(col2, 'NA') 
  FROM table) SRC
WHERE first <> 'NA'

这样做会生成一个名为src的内联视图，其中包含一个名为first的列。如果col1的{{1}}或col2为空，则它会将NA替换为该值。然后，它会将table和所需文字连接起来，排除first值为“NA”的记录

或者，如果您只是创建一个包含所需值的内联表并加入...

first

就个人而言，我发现第二个选项更容易阅读。虽然如果你对a，b，c有意义，我会认为你想要存储在某个地方的表中以便进行额外的访问。在代码中似乎是一个存储可能会改变的数据的坏地方。假设你想要

    SELECT First,  x.b as Second
    FROM (
      SELECT coalesce(col1, 'NA') as First 
      FROM Table
      UNION
      SELECT coalesce(col2, 'NA') 
      FROM table) SRC
    INNER JOIN (select a,b 
                from (values ('a', 'This is a'), 
                             ('b', 'To B or not to' ), 
                             ('c', 'I like cat whose name starts with')) as x(a,b)) X;
   on X.a = src.first
    WHERE first <> 'NA'

Answer 2

感谢xQbert 我可以像这样解决这个问题

SELECT FirstRow, concat
(
CASE FirstRow
WHEN 'AN' then 'amerstdam'
WHEN 'G' then 'berlin'
ELSE 'NA'
END, ''
) AS SecondRow
FROM(
    Select coalesce (Col1, 'NA') as FirstRow 
    FROM Table1
    UNION
    Select coalesce (Col2, 'NA')
    FROM Table1) SRC
WHERE FirstRow <> 'NA'
;

如何从第一个select语句访问输出

2 个答案: