Question

Say you had a long array of chars that are either 1 or 0, kind of like a bitvector, but on a database column. How would you query to know what values are set/no set? Say you need to know if the char 500 and char 1500 are ‘true’ or not.

Answer 1

SELECT   Id FROM   BitVectorTable WHERE   SUBSTRING(BitVector, 500, 1) = '1'   AND SUBSTRING(BitVector, 1000, 1) = '1' 

No index can be used for this kind of query, though. When you have many rows, this will get slow very quickly.

Edit: On SQL Server at least, all built-in string functions are deterministic. That means you could look into the possibility to make computed columns based on the SUBSTRING() results for the whole combined value, putting an index on each of them. Inserts will be slower, table size will increase, but searches will be really fast.

SELECT   Id FROM   BitVectorTable WHERE   BitVector_0500 = '1'   AND BitVector_1000 = '1' 

Edit #2: The limits for SQL Server are:

• 1,024 columns per normal table
• 30.000 columns per ‘wide’ table