MySQL查询使用where和group by子句

Question

I have the following table.

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

I want to use GROUP BY clause in my project. I am getting an error when I am using the query:

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

Error

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

The following query should work.

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

Remember, the where clause goes before the group by clause and all non-aggregated terms in the select part will have to be present in the group by clause.

Answer 2

Use the having clause instead of where

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

Regards.