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)