SELECT DISTINCT table1.column1, table1.column2, table2.column3 FROM table1 LEFT JOIN table2 ON table1.key = table2.key;
2.使用GROUP BY语句聚合数据
SELECT table1.column1, table1.column2, SUM(table2.column3) FROM table1 LEFT JOIN table2 ON table1.key = table2.key GROUP BY table1.column1, table1.column2;
3.使用子查询去除重复数据
SELECT table1.column1, table1.column2, table2.column3 FROM table1 LEFT JOIN ( SELECT DISTINCT key, column3 FROM table2 ) table2 ON table1.key = table2.key;