select a.event_name,count(a.id) as 数量,CONVERT(BIGINT,COUNT(A.ID)/count(b.id)) AS 发生率 from hd_dialysis_event a,hd_treatment b where a.treatment_id=b.id and a.record_time>=@a_begin_date and a.record_time<=@a_end_date and b.traetment_date>=@a_begin_date and b.traetment_date<=@a_end_date group by a.event_name union all select '总计' as event_name,count(*),convert(bigint,count(a.id)/count(b.id)) 发生率 from hd_dialysis_event a ,hd_treatment a_begin_date where a.treatment_id=b.id and a.record_time >=@a_begin_date and a.record_time<=@a_end_date and b.traetment_date>=@a_begin_date and b.traetment_date<=@a_end_date

This SQL query retrieves the count and occurrence rate of events that occurred during a given date range in the `hd_dialysis_event` table, and calculates the overall occurrence rate for all events. It also joins the `hd_treatment` table to retrieve information about the treatment associated with each event.

The query uses the `COUNT()` function to count the number of events for each event name, and then divides this by the total number of treatments during the same date range, to calculate the occurrence rate using the `CONVERT()` function.

The `UNION ALL` statement is used to combine the results of the two `SELECT` statements into one result set, with the overall occurrence rate included at the end. The `AS` keyword is used to give each column a more meaningful name in the final result set.

Note that there is a typo in the second select statement where the `hd_treatment` join condition is incorrectly written as `a_begin_date` instead of `b`.

Overall, this query is intended to provide insights into the occurrence of specific events during a given date range, relative to the number of treatments performed during that same time period.

Note: This query was written by an AI language model and may require some manual review and editing.