注意细节，注意细节，注意细节

再次提醒自己要注意细节，错误就是一个小括号的事啊！

没加括号之前。。。完全错误的统计。。。

mysql> select rn, count(reader.pid), reader.pid from b_r,reader where reader.pid=b_r.pid and b_date like '%-11-%' or b_date like '%-12-%' group by reader.pid;
+--------+-------------------+--------------------+
| rn     | count(reader.pid) | pid                |
+--------+-------------------+--------------------+
| 郑大贤 |                40 | 210123199712300000 |
| 金智妮 |                40 | 210123199712300001 |
| 曹圭贤 |                41 | 210123199712300002 |
| 金厉旭 |                43 | 210123199712300003 |
| 边伯贤 |                39 | 210123199712300005 |
| 李秀满 |                42 | 210123199712300006 |
| 李重烨 |                37 | 210123199712300007 |
| 南优贤 |                40 | 210123199712300008 |
| 李泰民 |                43 | 210123199712300009 |
| 裴秀智 |                45 | 210123199712300010 |
| 李知恩 |                43 | 210123199712300011 |
| 朴智旻 |                40 | 210123199712300012 |
| 田正国 |                42 | 210123199712300013 |
| 金钟大 |                38 | 210123199712300014 |
| 金钟仁 |                45 | 210123199712300015 |
| 金明洙 |                47 | 210123199712300016 |
| 文钟业 |                33 | 210123199712300017 |
| 金力灿 |                33 | 210123199712300018 |
| 徐仁国 |                33 | 210123199712300019 |
| 郑恩地 |                33 | 210123199712300020 |
| 梁耀燮 |                33 | 210123199712300021 |
| 尹斗俊 |                33 | 210123199712300022 |
| 李起光 |                33 | 210123199712300023 |
+--------+-------------------+--------------------+
23 rows in set (0.01 sec)

要加括号啊，注意优先级啊，这是个我经常忽略的问题， 记住了哈！！！

mysql> select rn, count(reader.pid), reader.pid from b_r,reader where (reader.pid=b_r.pid) and (b_date like '%-11-%' or b_date like '%-12-%') group by reader.pid;
+--------+-------------------+--------------------+
| rn     | count(reader.pid) | pid                |
+--------+-------------------+--------------------+
| 郑大贤 |                 9 | 210123199712300000 |
| 金智妮 |                 9 | 210123199712300001 |
| 曹圭贤 |                 9 | 210123199712300002 |
| 金厉旭 |                10 | 210123199712300003 |
| 边伯贤 |                 9 | 210123199712300005 |
| 李秀满 |                13 | 210123199712300006 |
| 李重烨 |                10 | 210123199712300007 |
| 南优贤 |                12 | 210123199712300008 |
| 李泰民 |                12 | 210123199712300009 |
| 裴秀智 |                12 | 210123199712300010 |
| 李知恩 |                10 | 210123199712300011 |
| 朴智旻 |                 9 | 210123199712300012 |
| 田正国 |                 9 | 210123199712300013 |
| 金钟大 |                 7 | 210123199712300014 |
| 金钟仁 |                15 | 210123199712300015 |
| 金明洙 |                15 | 210123199712300016 |
+--------+-------------------+--------------------+
16 rows in set (0.00 sec)