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Messages 1 to 2 of 2 total |
Use of compound indexes |
Mon, May 22 2006 10:15 AM | Permanent Link |
"Jose Eduardo Helminsky" | Tim
I've asked this before but... Since DBISAM use only the first field of any index for SQL processing, I want to make a suggestion: 1) Follow the standards and change the way DBISAM handle this (a lot of work) 2) Create a DBISAM proprietary function to "help" DBISAM to read more than one field. IOW, developers know when there are indexes available to filter data. My suggestion is something like: select * from table where joinfields('f1','f2') = (123,'2006-05-22') The need of just one index with f1 and f2 fields instead of select * from table where f1=123 and f2='2006-05-22' The need of two indexes, one with f1 and another with f2. Sometimes there are 4 or 5 comparations and if you have more than 1 million records the first method will be faster. This is just a suggestion, may be the first option will be better. Eduardo |
Mon, May 22 2006 11:38 AM | Permanent Link |
Tim Young [Elevate Software] Elevate Software, Inc. timyoung@elevatesoft.com | Eduardo,
<< Since DBISAM use only the first field of any index for SQL processing, I want to make a suggestion: >> This is on the list. It had to wait for version 5 due to the way that 4.x and earlier versions were indexed and the way that data such as floating-point fields was bit-flipped. Version 5 doesn't do that anymore, so it can use indexes just like record data and perform brute-force scans. -- Tim Young Elevate Software www.elevatesoft.com |
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