SQL Interview questions -5

26)How does one find the next value of a sequence?

Perform an "ALTER SEQUENCE ... NOCACHE" to unload the unused cached sequence numbers from the Oracle library cache. This way, no cached numbers will be lost. If you then select from the USER_SEQUENCES dictionary view, you will see the correct high water mark value that would be returned for the next NEXTVALL call. Afterwards, perform an "ALTER SEQUENCE ... CACHE" to restore caching.

You can use the above technique to prevent sequence number loss before a SHUTDOWN ABORT, or any other operation that would cause gaps in sequence values.

27)Workaround for snapshots on tables with LONG columns

You can use the SQL*Plus COPY command instead of snapshots if you need to copy LONG and LONG RAW variables from one location to another. Eg:

COPY TO SCOTT/TIGER@REMOTE     -

CREATE IMAGE_TABLE USING       -

       SELECT IMAGE_NO, IMAGE  -

       FROM   IMAGES;

Note: If you run Oracle8, convert your LONGs to LOBs, as it can be replicated.