Yes thank you, very useful information as always (: It seems that im still learning something new every day.
----- Original Message ----- From: "A. Razzak Memon" <[EMAIL PROTECTED]> To: "RBASE-L Mailing List" <[EMAIL PROTECTED]> Sent: Monday, October 20, 2003 3:04 PM Subject: [RBASE-L] - Re: index on multiple columns - Razzak's Reply > At 02:36 PM 10/20/2003 -0700, Alan Wolfe wrote: > > >hello, sorry if i should just rtfm but i was wondering, last night i heard > >that you could set up an index on multiple columns without storing the > >concatenation of those columns. > > > >I was wondering, how would you set up such an index and how > >would you use it in your selects? > > > Alan, > > Technically, if it can, R:BASE will do index-only > retrieval. This is the fastest method of retrieving > data. > > When the columns selected for display are limited > to the column or columns in the index used in the > WHERE clause, R:BASE will retrieve the data as it > reads the index information from file 3. It does > not need to look at the data stored in file 2. > > Index-only retrieval is done only when the columns > to be retrieved are all included in the index. > > Multi-Column Indexes are also very useful. If you > routinely select the same set of columns (up to eight), > consider defining a multi-column index for use with > index-only retrieval. > > Keep in mind that only full-text indexed and non-text > indexes can be used for index-only retrieval -- thus > all pieces of the multi-column index must be full-text > or non-text to store the actual data values in file 3. > > When defining a multi-column index, you are limited > to a total of 200 bytes for the index value. Text > values store the index value in a 4-byte segments, > therefor a TEXT 6 column defined as a full-text > index actually is stored as 8-bytes in file 3. > > Database with INDEXes will also require a regular > maintenance of database. > > R:BASE 6.5++ (Build:1.866xRT03) and R:BASE 7.0 for > Windows includes *new* PACK INDEX command in a > multi-user environment. > > Example 01: > > PACK INDEX FOR TableName > > This will pack all the indices for the specified > table, even in a Multi-User environment. > > Example 02: > > PACK INDEX > > This will pack all the indices for currently > CONNected database, even in a Multi-User environment. > > Hope that helps! > > Very Best R:egards, > > Razzak. >
