Mysql 查询使用 where 和 group by 子句

Question

我有下表。

mysql> select * from consumer9;
+------------+--------------+-------------------+
| Service_ID | Service_Type | consumer_feedback |
+------------+--------------+-------------------+
|        100 | Computing    |                -1 |
|         35 | Printer      |                 0 |
|         73 | Computing    |                -1 |
|         50 | Data         |                 0 |
+------------+--------------+-------------------+

我想在我的项目中使用GROUP BY子句。我在使用查询时遇到错误:

SELECT  Service_ID, Service_Type, SUM(consumer_feedback) 
FROM consumer9 
GROUP BY Service_ID 
WHERE Service_Type=Printer;

错误

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'where Service_Type=Printer' at line 1

Answer 1

以下查询应该有效。

select Service_ID, Service_Type, sum(consumer_feedback) 
from consumer9 
where Service_Type=Printer
group by Service_ID, Service_Type;

请记住，where 子句位于 group by 子句之前，并且 select 部分中的所有非聚合术语都必须出现在 group by 子句中。