Using binary in MySQL and PHP for flags

Question

Let's say I have the following flags that can be attached to a customer:

1 Hot
2 Urgent
4 Sensitive
8 Confidential

In my table I would store an active customer as an int of 6.

I figured doing things this way would save me a reference table and make querys faster.

How do I get PHP to interpret a 6 and for example light up a customer and active icon?

Someone can really be active without being a customer? A prospect can be cancelled? A prospect can be a customer? I think you need to think harder about the flags and the states they represent. — Gordon Linoff
– Gordon Linoff, Commented Oct 12, 2015 at 14:34
Those are just quick examples. I have renamed them for you. Non are exclusive now but I get what you are saying. — imperium2335
– imperium2335, Commented Oct 13, 2015 at 5:40

woz · Accepted Answer · 2015-10-12 14:48:54Z

1

Bitwise operators will do the trick:

$flag = 6; // value from the database
$customer = 2; // constant value
$active = 4; // constant value

if ($flag & $customer)
{
    print 'I am a customer.';
}

if($flag & $active)
{
    print 'I am active.';
}

I agree with @GordonLinoff though. Really consider if this is what you want because it's not easy to change later, and it could allow unexpected scenarios.

answered Oct 12, 2015 at 14:48

woz

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3 Comments

imperium2335 Over a year ago

so problems arise when one can not be without another?

woz Over a year ago

@imperium2335 yes, that's one example. Also consider the possibility that one classification is removed; or, a new one is added and should be a default all existing records. Also, in you original example, do prospects and customers really differ by only a flag? It's unlikely that your tables are normalized in that case. I'm not saying don't ever use bitwise flags, but just think carefully about whether it's appropriate.

imperium2335 Over a year ago

No, that was a poor example, realistically there is a column for state, being prospect or customer. Those definitions are stored in a separate table.

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