将列复杂串联成一列

Question

我有这个代码：

SELECT DISTINCT
CASE
    WHEN abc > def THEN 'abc is larger than def'::text
    ELSE NULL::text
END AS case1,
CASE
    WHEN abc < ghi THEN 'def is larger than abc'::text
    ELSE NULL::text
END AS case2,
CASE 
    WHEN abc > jkl THEN 'abc is larger than jkl'::text
    ELSE NULL::text
END AS case3,

看起来像这样：

-------------------------------------------------------------------------------------
|              case1          |           case2          |          case3           |
-------------------------------------------------------------------------------------
|    'abc is larger than def' | 'def is larger than abc' | 'abc is larger than jkl' |
-------------------------------------------------------------------------------------

我想做的是创建一个名为 'casesCombined' 的列，而不是合并“then's”。例如，如果前 2 个案例为真，则 'casesCombined' 列将为 '"abc is larger than def", "def is larger than abc"'.

像这样：

-----------------------------------------------------
|                  casesCombined                    |
-----------------------------------------------------
| 'abc is larger than def', 'def is larger than abc'|
-----------------------------------------------------

试了很多方法，都搞不明白。我也不需要那些 'case1'、'case2'...

Answer 1

SELECT concat_ws(', ', CASE WHEN abc > def THEN 'abc is larger than def' END
                     , CASE WHEN abc < ghi THEN 'def is larger than abc' END
                     , CASE WHEN abc > jkl THEN 'abc is larger than jkl' END
                ) AS cases_combined
FROM tbl;

当没有 ELSE 子句时，

CASE 默认为 NULL。
concat_ws() 忽略 NULL 值。

我没有添加额外的单引号，因为我假设您实际上并不想要结果中的那些。如果您这样做，只需添加：

Insert text with single quotes in PostgreSQL

将列复杂串联成一列

Complex concatenation of columns into one column

postgresql

null

case

string-concatenation