1) What is dense ranking?
2) Difference between Substring and Instring?
3) Case and Decode?
4) Pseudo column?
5) View vs Materialized views?
6) SQl performance tuning?
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Answer Posted / ssk
1. DENSE_RANK is an Analytical Function which doesn't leave
gaps between the records. Coming to Rank function it leaves
gaps between the records.
Eg:
(RANK) (DENSE_RANK)
Sno Marks Ranks Sno Marks Ranks
----- ----- ----- ----- ----- -----
1 100 1 1 100 1
2 100 1 2 100 1
3 200 3 3 200 2
4 300 4 4 300 3
5 300 4 5 300 3
6 400 6 6 400 4
2. Substr will displays the text from position to TO position.
Instr returns the position of the character.
Eg: SELECT SUBSTR('ORACLE',2,4) FROM DUAL;
O/P : RAC
SELECT INSTR('ORACLE IS A DATABASE','A',1,2) from dual;
O/P : 11
3. PSEUDO Column : A column which is not an actual column in
the table. Eg : ROWNUM,ROWID,SYSDATE,USER,UID..
| Is This Answer Correct ? | 9 Yes | 0 No |
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