查询：
select a,b,c from table_name where a=1
统计特定字段的总行数
select count(spec),spec from table_name where spec='dida' group by spec;
示例结果：
+-------+------------------+
| count | spec|
+-------+------------------+
| 8 | dida |
+-------+------------------+
1 row in set
