在两个左连接的表中，如果要避免重复聚合列的值，可以使用子查询或者临时表来实现。

方法一：使用子查询

SELECT t1.group_id, t1.column1, t2.column2
FROM (
    SELECT group_id, column1
    FROM table1
    GROUP BY group_id, column1
) AS t1
LEFT JOIN (
    SELECT group_id, column2
    FROM table2
    GROUP BY group_id, column2
) AS t2 ON t1.group_id = t2.group_id

方法二：使用临时表

CREATE TABLE temp_table1 AS 
SELECT group_id, column1
FROM table1
GROUP BY group_id, column1;

CREATE TABLE temp_table2 AS 
SELECT group_id, column2
FROM table2
GROUP BY group_id, column2;

SELECT t1.group_id, t1.column1, t2.column2
FROM temp_table1 AS t1
LEFT JOIN temp_table2 AS t2 ON t1.group_id = t2.group_id;

DROP TABLE temp_table1;
DROP TABLE temp_table2;

以上两种方法都是先对每个表进行分组，然后再进行左连接操作，可以确保在两个表中不会出现重复的聚合列值。