按照 sql_finger_md5 分组取query_time_ms 最大的一行数据。
使用any函数可以去匹配到的第一行数据,所以可以先让数据按照query_time_ms 排序,然后再使用group by 和any结合取第一行数据,就是最大值的那一行数据。
selectany (time) as time ,any (query_time_ms) as query_time_ms ,any (sqltext) as sqltext,any (inst_id) as inst_id,any (inst_name) as inst_name,any (dbname) as dbname,any (host_address) as host_address,any (lock_times) as lock_times,any (parse_row_counts) as parse_row_counts,any (return_row_counts) as return_row_counts,any (sql_finger) as sql_finger,sql_finger_md5,any (sqltext_md5) as sqltext_md5
FROM(SELECTinst_id,inst_name,dbname,execution_start_time as time,host_address,query_time_ms,sqltext,lock_times,parse_row_counts,return_row_counts,sql_finger,sql_finger_md5,sqltext_md5FROMcmdb.rds_all_slow_sql_record_distributedWHERE(execution_start_time >= toDateTime(1711079437) AND execution_start_time <= toDateTime(1711684237) )AND (dbname = 'leopard_admin')AND host_address not like '%root%' AND host_address not like '%bi_user%' AND sqltext not like '%insert%'order by sql_finger_md5 desc,query_time_ms desc) a
group bya.sql_finger_md5
order by query_time_ms desc
limit1000
窗体函数在数据量大的时候性能堪忧,在clickhouse中还有其他的处理方式。比如使用any()、anyLast()函数。
按官方文档的定义:any() “selects the first encountered value.”,也就是返回遇到的首个值,看上去是很符合当前的情况。但文档又做了说明:因为查询可能是以任意顺序执行的,并且可能每次执行得顺序都不同(如同我们上面的select * from user_order返回的行顺序不同),所以这个函数的执行结果可能是不确定的。如果要获得确定的值,可以使用“min”或者“max”。或者,select的对象的是一个已经排序过的子查询。
参考资料:
http://www.tracefact.net/tech/112.html