MYSQL - 将 UNION ALL 的 GROUP_CONCAT 结果合并为一行

Question

我有以下声明:

SELECT DISTINCT Concat("table1.", column_name) 
FROM   information_schema.columns 
WHERE  table_name = "table1" 
UNION ALL 
SELECT DISTINCT Concat("table2.", column_name)  
FROM   information_schema.columns 
WHERE  table_name = "table2";

产生以下结果:

+---------------------------------+
| CONCAT("table1.", column_name)  |
+---------------------------------+
| table1.column1                  |
| table1.column2                  |
| table1.column3                  |
| table2.column4                  |
| table2.column5                  |
| table2.column6                  |
| table2.column7                  |
+---------------------------------+

我希望它采用以下格式:

+-----------------------------------------------------------------------------------------------------------+
| CONCAT("table1.", column_name)                                                                            |
+-----------------------------------------------------------------------------------------------------------+
| table1.column1,table1.column2,table1.column3,table2.column4,table2.column5,table2.column6,table2.column7  |
+-----------------------------------------------------------------------------------------------------------+

我试过像这样使用 GROUP_CONCAT:

SELECT Group_Concat(DISTINCT Concat("table1.", column_name)) 
FROM   information_schema.columns 
WHERE  table_name = "table1" 
UNION ALL 
SELECT Group_Concat(DISTINCT Concat("table2.", column_name)) 
FROM   information_schema.columns 
WHERE  table_name = "table2";

但这错误地产生了以下结果:

+--------------------------------------------------------------+
| CONCAT("table1.", column_name)                               |
+--------------------------------------------------------------+
| table1.column1,table1.column2,table1.column3                 |
| table2.column4,table2.column5,table2.column6,table2.column7  | 
+--------------------------------------------------------------+

由此我自然而然地尝试将它作为子查询来执行 GROUP_CONCAT，如下所示:

SELECT GROUP_Concat(
    SELECT Group_Concat(DISTINCT Concat("table1.", column_name)) 
    FROM   information_schema.columns 
    WHERE  table_name = "table1" 
    UNION ALL 
    SELECT Group_Concat(DISTINCT Concat("table2.", column_name)) 
    FROM   information_schema.columns 
    WHERE  table_name = "table2" t)
FROM t;

但是上面的语句存在语法错误。我如何将 UNION ALL 的结果连接成一行？

我已经复习了以下问题但没有成功:

Combing results from union all into one row when some columns have different values

How do I combine two queries (union all) into one row?

MySQL COUNT results of UNION ALL statement

这与我之前的问题有点相关: MySQL - Subquery in SELECT clause

Answer 1

你快到了，试试这个:

select group_concat(xxx) from (
  SELECT DISTINCT Concat("table1.", column_name)  as xxx
  FROM   columns 
  WHERE  table_name = "table1" 
  UNION ALL 
  SELECT DISTINCT Concat("table2.", column_name)  
  FROM   columns 
  WHERE  table_name = "table2"
) as src;

老实说 - 你需要这个 UNION 做什么？这会做同样的事情......

SELECT  
  group_concat(distinct concat (table_name, '.', column_name) )
from columns 
WHERE table_name in ('table1', 'table2');

检查 fiddle :http://sqlfiddle.com/#!9/d1172