sql查询:从表行按Id构建，后面是Sym Pos顺序

Question

表格：

+-----+-----+----+ 
| Sym | Pos | Id | 
+-----+-----+----+ 
| a   | 0   | 0  | 
| b   | 1   | 0  | 
| c   | 2   | 0  | 
| a   | 0   | 1  | 
| d   | 1   | 1  | 
| b   | 0   | 2  | 
+-----+-----+----+ 

需要从此表的Id行构建，这将在订单Sym位置遵循。在这种情况下，这将是：

+-----+----+ 
| str | Id | 
+-----+----+ 
| abc | 0  | 
| ad  | 1  | 
| b   | 2  | 
+-----+----+

Answer 1

使用GROUP BY和特定于MySQL的聚合函数GROUP_CONCAT

SELECT GROUP_CONCAT(Sym ORDER BY Pos SEPARATOR '') AS str, Id
FROM yourtable
GROUP BY id

Answer 2

看看如何使用GROUP_CONCAT()