窗口函数的名字是over()函数,常用的有两个属性partition by和order by,partition by类似于group by,我们通常将group by叫做分组,而partition by称作分区。 一般结构为: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 Function(arg1 , arg2 ……) over(partition by
从sql order by elapased部分可以看出这个语句占用的 db time比例不高,从sql语句的执行上还是没有问题的,但是通过sql order by gets和execution这两个部分,可以很明显的看到,这条语句是top 1的语句,使用的buffer gets高达1T,这个表中的数据量就几千条数据,大小都是MB级别的,但是在10分钟内却能使用1T的buffer ...
1 SELECT EXECUTIONS,DISK_READS,BUFFER_GETS, 2 ROUND((BUFFER_GETS-DISK_READS)/BUFFER_GETS,2) Hit_radio, 3 ROUND(DISK_READS/EXECUTIONS,2) Reads_per_run, SQL_TEXT 4 FROM V$SQLAREA WHERE EXECUTIONS>0AND BUFFER_GETS >05 AND(BUFFER_GETS-DISK_READS)/BUFFER_GETS <0.86 ORDER BY4DESC; 16、用...
SELECT EXECUTIONS , DISK_READS, BUFFER_GETS, ROUND((BUFFER_GETS-DISK_READS)/BUFFER_GETS,2) Hit_radio, ROUND(DISK_READS/EXECUTIONS,2) Reads_per_run, SQL_TEXT FROM V$SQLAREA WHERE EXECUTIONS>0 AND BUFFER_GETS > 0 AND (BUFFER_GETS-DISK_READS)/BUFFER_GETS < 0.8 ORDER BY 4 DESC; 索引是...
命中率=1-(physical reads/(dbblock gets+ consistent gets)) Redo size:执行DML语句产生的重做日志大小 Sorts(memory,disk)在内存或者磁盘中的排序的数量。 注意:以上信息我们关注的主要是物理读和命中率,物理读过多说明从磁盘获取的数据就多,可能存在全表扫描,使得数据库的性能下降。命中率过低意味1、物理读过多...
,round( rows_processed / executions,2 ) avg_rows, round(disk_reads/executions ) avg_disk_reads,round(buffer_gets /executions ) avg_buffer_gets FROM `gv$plan_cache_plan_stat` s LEFT JOIN `gv$database` d ON (s.tenant_id =d.tenant_id AND s.db_id =d.database_id ) ...
For example, suppose that your interactive application runs a query that returns 50 rows. This application initially fetches only the first 25 rows of the query to present to the end user. You want the optimizer to generate a plan that gets the first 25 records as quickly as possible so th...
order by DISK_READS desc)where rownum <=3 28、逻辑读查询 select *from (select BUFFER_GETS,username,PARSING_USER_ID,sql_id,ELAPSED_TIME/1000000,sql_text from v$sql,dba_users where user_id=PARSING_USER_ID order by BUFFER_GETS desc)where rownum <=3 ...
The order gets applied from left to right in the expression list and may either be sorted in ascending or descending order depending on the optionally specified sort direction. The default sort direction is ascending. U-SQL always orders null values last, regardless of the sort direction or...
SELECT last_name, first_name FROM hr.employees WHERE last_name LIKE 'K%' ORDER BY last_name, first_name; The database retrieves all rows satisfying theWHEREcondition, also called thepredicate, in a single step. The database can pass these rows as a unit to the user, to another SQL ...