Pleeease...What is the cursor, index, and cluster?with an example

Mr_Shihab · #1 (**permalink**) 04-27-04, 05:21

I studied computer sience in the university?
In my study we practice some SQL statements with Oracle, and SQL Server
Also, We studied some database concepts like
But, until now I haven't clear opinion about CLUSTERS, INDEXES, and CURSORS in the database?

Please give an overview about them with small examples to clarify

Thank you very much

hurmavi · #2 (**permalink**) 04-28-04, 05:36

Hi!

Some fast ansvers:

CLUSTERS - this depends very much what product you are talking. Usually this has something to do how the data is located on the disk.
INDEXES - THE MOST INPORTANT feature in real life. Is a physical data structure, typically a b-tree. They are invisble to the SQL-queries, but have a tremendous performace issue.
CURSORS - SQL query usually returns many rows. C, COBOL etc. 3GL-languages can read only one row a time. That's why those program languages need to define a cursor, a feature that allows program to read one row in time.

Cheers, Bill

Nocopy · #3 (**permalink**) 05-02-04, 18:06

Quote:

Originally Posted by hurmavi

Hi!

Some fast ansvers:

CLUSTERS - this depends very much what product you are talking. Usually this has something to do how the data is located on the disk.
INDEXES - THE MOST INPORTANT feature in real life. Is a physical data structure, typically a b-tree. They are invisble to the SQL-queries, but have a tremendous performace issue.
CURSORS - SQL query usually returns many rows. C, COBOL etc. 3GL-languages can read only one row a time. That's why those program languages need to define a cursor, a feature that allows program to read one row in time.

Cheers, Bill

Bill, you probably wanted to say that if you DON'T have indexes than you will have a performance issue.

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