分组计数：
You can use COUNT() if you want to find out how many pets each owner has:

mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner;

ONLY_FULL_GROUP_BY参数开启与未开启区别

If the ONLY_FULL_GROUP_BY SQL mode is enabled, an error occurs:

mysql> SET sql_mode = 'ONLY_FULL_GROUP_BY';
Retrieving Information from a Table
265
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT owner, COUNT(*) FROM pet;
ERROR 1140 (42000): In aggregated query without GROUP BY, expression
#1 of SELECT list contains nonaggregated column 'menagerie.pet.owner';
this is incompatible with sql_mode=only_full_group_by

If ONLY_FULL_GROUP_BY is not enabled, the query is processed by treating all rows as a single
group, but the value selected for each named column is indeterminate. The server is free to select
the value from any row:

mysql> SET sql_mode = '';
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT owner, COUNT(*) FROM pet;
+--------+----------+
| owner | COUNT(*) |
+--------+----------+
| Harold | 8 |
+--------+----------+
1 row in set (0.00 sec)

假如有一个商品的数据表，请查找出价格最贵的一件商品的名称以及价格

SELECT name,MAX(price) AS price FROM shop;

also:

SELECT article, dealer, price
FROM shop
WHERE price=(SELECT MAX(price) FROM shop);