[DUG] Using Boolean (Char(1)) in Firebird

[russell]

Hi Steve

 

The topic you refer to is index selectivity. If you have a table with an
index involving one field and it has only two values the index is not as
useful in searches as  is, say a primary key fields which has a unique value
for each row. Of course "useful" depends on your needs.

 

<Select * from MyTable where myBool ='F' >  will return half the table.

 

See http://www.firebirdfaq.org/faq167/ "index selectivity"

 

This poor performance is not a FB feature, it is a common DB feature (I
think). To get a well performing index, make it with thought for what you
want the index to help you with.

 

HTH

 

Russell

 

From: Steve Peacocke [mailto:steve at peacocke.net] 
Sent: Sunday, 30 March 2014 8:32 p.m.
To: russell at belding.co.nz; NZ Borland Developers Group - Delphi List
Subject: Re: [DUG] Using Boolean (Char(1)) in Firebird

 

Thanks Russell,

 

Yes, I created a domain ..

 

  CREATE DOMAIN BOOL

   AS Smallint

   DEFAULT 0

   NOT NULL

  ;

 

And while it is possible to place an index on it, it's my understanding that
Firebird will not perform well when placing an index on this type of field
where there is limited ranges (e.g. M/F; 1/0; Y/N).

 

It was my understanding that Firebird may not even create this type of
index. Perhaps I am wrong??

 

Steve Peacocke
Mobile: +64 220 612-611

Linkedin Professional Profile
<http://nz.linkedin.com/pub/steve-peacocke/1/a06/489> 

 

On Sun, Mar 30, 2014 at 7:31 PM, russell <russell at belding.co.nz> wrote:

Hi Steve

 

Firebird Fb does not have a native boolean type. 

I use a smallint for my Boolean types. 1=True, 0=F. 

There are many ways to define and use Booleans in Fb.

Eg. CREATE TABLE BCD_CONNECTIONS (

       CONNECTION_ID ID /*Integer NOT NULL*/ NOT NULL,

       FIRST_TS TIMESTAMP NOT NULL,

       CURRENT_TS TIMESTAMP NOT NULL,

       MACHINE TEXT24 /*Varchar(24) */ DEFAULT 'Unknown' NOT NULL,

       SECURITY_CODE TEXT48 /*Varchar(48) */ DEFAULT 'illegal' NOT NULL,

       MACHINE_ID Integer,

       USER_ID Integer,

       USER_NAME TEXT64 /*Varchar(64) */,

       B_IN_WINSLEEP Smallint DEFAULT 0,

       CONSTRAINT BCD_CONNECTIONS_PK PRIMARY KEY (CONNECTION_ID)

);

 

So these Booleans can be indexed. Tables can have many Booleans.

ID, TEXTNN are my defined Domains in Fb.

 

Russell

 

From: delphi-bounces at listserver.123.net.nz
[mailto:delphi-bounces at listserver.123.net.nz] On Behalf Of Steve Peacocke
Sent: Sunday, 30 March 2014 3:19 p.m.
To: NZ Borland Developers Group - Delphi List
Subject: [DUG] Using Boolean (Char(1)) in Firebird

 

Hi all,

 

I'm playing around with a Firebird database and wanted to know from you DB
experts out there how you handle booleans in a table.

 

These could be as simple as

  ActiveRecord (Y/N)

  AccountTransactionType (I/E) - (Income or Expense)

 

That last I would normally think would be "Income (Y/N)" so that would be a
boolean too.

 

My understanding is that this will never be indexed, even if you
specifically add an index to it. So how do you handle it. There may be
several boolean fields in a table definition.

 

As these tables c an contain several hundred thousand records, this could
potentially slow down any query to say total all records last 3 years where
Active and Income - as the only index would then be on the date field, there
is a possibility that this could potentially be a very slow query.

 

I've heard of others creating another table to create, say, non-Avtive
record ID's, but this one table could have several booleans, therefore
creating several new tables (combining then into a single table with the
field name would cause the same problem).

 

Any thoughts?



Steve Peacocke
Mobile: +64 220 612-611 <tel:%2B64%20220%20612-611> 

Linkedin Professional Profile
<http://nz.linkedin.com/pub/steve-peacocke/1/a06/489> 


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