Subject Re: [firebird-support] Index process in Firebird 2.1.4
Author Ann Harrison
Post date 2017-10-22T11:24Z


On Oct 19, 2017, at 11:45 PM, gn7soft@... [firebird-support] <firebird-support@yahoogroups.com> wrote:

Hi!
I'm going to develop a commercial program with Firebird2.1, in Delphi7.

As noted, 2.1 is obsolete. 

I want to know whether the following index is picked by the optimizer.

[The first question]
CREATE INDEX IDX1 ON PROJECT(A)
CREATE INDEX IDX2 ON PROJECT(B)
CREATE INDEX IDX3 ON PROJECT(C)
CREATE INDEX IDX4 ON PROJECT(D)

SELECT * PROJECT WHERE A=1 and B=2 and C=3 and D=4

The optimizer would be choose the fastest way among table-full-scan and four indexs. Is this right?


If columns A, B, C, and D all have a lot of different values - think of street addresses rather than eye color - then Firebird can use all four indexes. It builds bit maps of matching records from each index and finds records that match all the criteria. 

Note that the SHOW PLAN command shows only the first index for any table - maybe newer versions show more...

Good luck,

Ann


[The second question]
CREATE INDEX IDX1 ON PROJECT(A)
CREATE INDEX IDX2 ON PROJECT(B,C,D)

SELECT * PROJECT WHERE A=1 and B=2 and C=3 and D=4

The optimizer would be choose the fastest way among table-full-scan and two indexs. Is this right?



[The third question]
CREATE INDEX IDX ON PROJECT(B,C,D)

SELECT * PROJECT WHERE A=1 and B=2 and C=3 and D=4

The optimizer would be c hoose the fastest way among table-full-scan and IDX index. Is this right?


Please tell me.
Thanks!