极复杂的SQL语句，求大神解释

CREATE TEMPORARY TABLE statistics_table_temp SELECT  * FROM (SELECT now) times, (SELECT client_ip,ruleid,event_type,severity FROM audit_table WHERE `tstamp` >= DATE_SUB(now, INTERVAL 10 MINUTE) AND `tstamp` < now) AS ret_statitics_table_temp;

INSERT INTO event_times_1hour(sttime, event_type, count) SELECT * FROM (SELECT now) times, (SELECT event_type,COUNT(event_type) AS total_count from statistics_table_temp group by event_type order by total_count desc) AS ret_event_times_1hour on duplicate key update count=total_count;
其中now是传递的参数

你的数据库应该不是oracle或者sqlserver应该是mysql吧，第一条语句可以拆分一下

     (SELECT client_ip,ruleid,event_type,severity FROM audit_table WHERE `tstamp` >= DATE_SUB(now, INTERVAL 10 MINUTE) AND `tstamp` < now) AS ret_statitics_table_temp;//y一个select语句查询得到表ret_statitics_table_temp
     (SELECT now) times//得到表times
     SELECT  * FROM times，ret_statitics_table_temp//这个语句查询结果跟times left join ret_statitics_table_temp一样得到一张新的表
     CREATE TEMPORARY TABLE statistics_table_temp 新的表(也就是SELECT  * FROM times，ret_statitics_table_temp)//建立一个临时表statistics_table_temp，oracle是用的CREATE TEMPORARY TABLE statistics_table_temp as SELECT  * FROM times，ret_statitics_table_temp)

第二个语句就是你建立一个临时表后插入数据

    (SELECT event_type,COUNT(event_type) AS total_count from statistics_table_temp group by event_type order by total_count desc) AS ret_event_times_1hour  on duplicate key update count=total_count；
    (SELECT now) times；
    SELECT * FROM times，ret_event_times_1hour；
    INSERT INTO event_times_1hour(sttime, event_type, count)  SELECT * FROM times，ret_event_times_1hour；