MYSQL - UNION ALL 的 GROUP_CONCAT 结果成一行答案

【问题标题】：MYSQL - GROUP_CONCAT results of UNION ALL into one rowMYSQL - UNION ALL 的 GROUP_CONCAT 结果成一行
【发布时间】：2015-04-14 14:55:12
【问题描述】：

我有如下声明：

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";

这会产生以下结果：

+---------------------------------+
| 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  |
+-----------------------------------------------------------------------------------------------------------+

我尝试过像这样使用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GROUP_CONCAT它作为子查询，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;

但是上面的语句有语法错误。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

这有点与我之前的问题有关： MySQL - Subquery in SELECT clause

【问题讨论】：

标签： mysql group-concat union-all

【解决方案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;

说实话 - 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');

检查小提琴：http://sqlfiddle.com/#!9/d1172

【讨论】：

谢谢我的好先生！您的第二个建议确实简化了陈述！

【解决方案2】：

SELECT GROUP_Concat(a) 

FROM (
    SELECT Group_Concat(DISTINCT Concat("table1.", column_name)) as a
    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
GROUP BY 1

【讨论】：

感谢 Alex 的回答，但我仍然收到 ERROR 1064 (42000): You have an error in your SQL syntax...