mysql> SELECT vend_id FROM products;
+---------+
| vend_id |
+---------+
|    1001 |
|    1001 |
|    1001 |
|    1002 |
|    1002 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1005 |
|    1005 |
+---------+
14 rows in set (0.00 sec)

mysql> SELECT vend_id,COUNT(*) AS num_prods
-> FROM products                  #先分组，再分别计算COUNT（*）
-> GROUP BY vend_id;
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
|    1001 |         3 |
|    1002 |         2 |
|    1003 |         7 |
|    1005 |         2 |
+---------+-----------+
4 rows in set (0.00 sec)
TIPS：

eg:
mysql> SELECT vend_id,COUNT(*) AS num_prods
-> FROM products
-> GROUP BY vend_id
-> HAVING COUNT(*)>2;        #从结果中过滤不符合COUNT(*)>2的组
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
|    1001 |         3 |
|    1003 |         7 |
+---------+-----------+
2 rows in set (0.00 sec)

eg:

mysql> SELECT vend_id,prod_price FROM products
-> ORDER BY prod_price;
+---------+------------+
| vend_id | prod_price |
+---------+------------+
|    1003 |       2.50 |
|    1003 |       2.50 |
|    1002 |       3.42 |
|    1003 |       4.49 |
|    1001 |       5.99 |
|    1002 |       8.99 |
|    1001 |       9.99 |
|    1003 |      10.00 |
|    1003 |      10.00 |
|    1003 |      13.00 |
|    1001 |      14.99 |
|    1005 |      35.00 |
|    1003 |      50.00 |
|    1005 |      55.00 |
+---------+------------+
14 rows in set (0.00 sec)
mysql> SELECT vend_id,COUNT(*) AS num_prods
-> FROM products
-> WHERE prod_price >14              #WHERE过滤后只剩下上表中最后3条记录，
-> GROUP BY vend_id                     #HAVING再过滤分组后vend_id为不符合COUNT(*) >=2组
-> HAVING COUNT(*) >=2;
+---------+-----------+
| vend_id | num_prods |
+---------+-----------+
|    1005 |         2 |
+---------+-----------+
1 row in set (0.00 sec)

TIPS：

 Examples:

mysql> SELECT order_num,quantity,item_price FROM orderitems;
+-----------+----------+------------+
| order_num | quantity | item_price |
+-----------+----------+------------+
|     20005 |       10 |       5.99 |
|     20005 |        3 |       9.99 |
|     20005 |        5 |      10.00 |
|     20005 |        1 |      10.00 |
|     20006 |        1 |      55.00 |
|     20007 |      100 |      10.00 |
|     20008 |       50 |       2.50 |
|     20009 |        1 |      10.00 |
|     20009 |        1 |       8.99 |
|     20009 |        1 |       4.49 |
|     20009 |        1 |      14.99 |
+-----------+----------+------------+
11 rows in set (0.00 sec)
mysql> SELECT order_num,SUM(quantity*item_price) AS ordertotal
-> FROM orderitems
-> GROUP BY order_num
-> HAVING SUM(quantity*item_price) >= 50;
+-----------+------------+                    #未用ORDERBY指定排序，结果可能不是想要的，例如按ordertotal升序
| order_num | ordertotal |
+-----------+------------+
|     20005 |     149.87 |
|     20006 |      55.00 |
|     20007 |    1000.00 |
|     20008 |     125.00 |
+-----------+------------+
4 rows in set (0.00 sec)
mysql> SELECT order_num,SUM(quantity*item_price) AS ordertotal
-> FROM orderitems
-> GROUP BY order_num
-> HAVING SUM(quantity*item_price) >=50
-> ORDER BY ordertotal;              # 用ORDERBY指定排序方式
+-----------+------------+
| order_num | ordertotal |
+-----------+------------+
|     20006 |      55.00 |
|     20008 |     125.00 |
|     20005 |     149.87 |
|     20007 |    1000.00 |
+-----------+------------+
4 rows in set (0.01 sec)

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