Hello,
I have a question regarding a limitation on indexes that I read in the
INFORMIX-4GL 4.0 Users Guide. The text from the guide is a follows...
. Do not index columns that contain a large number of duplicate
values, such as Y (for yes) or N (for no). Here the index can
significantly slow down the process of accessing values in the
indexed column. Moreover, you cannot have more than 65,536
occurrences of the same value in an indexed column-an important
consideration when designing a large database.
Well, I understand the logic of the first two sentences, but I have a
problem with the third...
Moreover, you cannot have more than 65,536
occurrences of the same value in an indexed column-an important
consideration when designing a large database.
Say if I have a table with a column that may contain one of 10 values,
and there will certainly be more than 65,536 occurrences of one/some/all of
the possible values in that column. My planned index on this table would
have this column as the last part of a composite index. According to the above
statement, this is not recommended. But, if the index is a composite index,
(which mine is) I don't see how the above statement applies.
My rationale is this: by the time the query processor gets to the last
part of this index the number of occurrences of the same value in the column
will be much less than 65,536.
Therefore, there shouldn't be a problem? ...right?
I'm I missing something... Do I not understand how the query processor
works... Is the above excerpt from the guide a typo...
Any ideas, suggestions, or actual experience with a similar dilemma
will be greatly appreciated.
Thank You,
Tom Leccese
Performance Software Inc.
voice: (201)-808-7062
email: uunet!4gen!psi!tom