SELECT only powers of 2

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I have a column in a table that contains integers. I am looking for a way to select only those rows that have integer powers of 2 in this column, such as 1, 2, 4, 8, 16, 32, 64, etc.

Thanks

Posted 18-Dec-12 9:38am

Rio Rico Rick

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Solution 2

You can use this How to tell if a number is a "POWER of 2"-number[^].

Posted 18-Dec-12 10:48am

André Kraak

Solution 1

Use mod, as in

where (x%2 = 0)

Oh, powers of 2. All you have is SQRT. I would probably use a temporary table containing all the numbers you want, and match values that are in that table.

Posted 18-Dec-12 9:42am

Christian Graus

Updated 18-Dec-12 9:45am

v2

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Wendelius · Accepted Answer · 2012-12-18T10:48:00

You didn't mention the database but if you're using Sql Server 2012 then one way is to use LOG[^] function.

For example:

SQL

SELECT ...
FROM SomeTable
WHERE LOG(SomeField, 2) = ROUND(LOG(SomeField, 2), 0)

That should return all the rows where the field contains a number which is a power of 2.

A bit more explanation in Get powers of 2 with Sql Server 2012[^]

Rio Rico Rick · Accepted Answer · 2012-12-20T05:31:00

Thanks Mika!

I did it using the sql server 2008 version of log. At first I was getting a type conversion error, but I ended up fixing it (somehow).

WHERE (LOG(ServiceMask) / LOG(2)) != CONVERT(int, (LOG(ServiceMask) / LOG(2)))

I found out the hard way that LOG really means LN here. So I converted to base 2.

SELECT only powers of 2

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