group by is used when we use aggregate functions on the columns in a query the other columns should be in group by query
select empno,ename,sum(sal) from emp group by empno,ename
Order by is used to sort values either in ascending or descending order
A DBA had to remove some Archivelogs to free up space in filesystem. Now when the RMAN job starts to backup Archivelogs, it complains about missing Archivelogs that were deleted by DBA. To resolve the issue and continue backing up remainder of Archivelogs, which RMAN command can be used so it wo not complain about missing Archivelogs.
By running $ORACLE_HOME/rdbms/admin/spcreate.sql script
► Run a TOP command in Unix to see CPU usage (identify CPU killer processes)
► Run VMSTAT, SAR, and PRSTAT command to get more information on CPU and memory usage and possible blocking
► Run STATSPACK report to identify:
1. TOP 5 WAIT EVENTS
2. RESOURCE intensive SQL statements
► See if STATISTICS on affected tables needs to be re-generated
► IF poorly written statements are culprit, run a EXPLAIN PLAN on these statements and see whether new index or use of HINT brings the cost of SQL down.