比较char字段和位掩码

Question

I'm trying to select rows by a charfield with the length of 9. It is in collation utf8_gen.

My where-condition is that the first n bits of a stored value have to match my given bitmask.

One example:

data:

id  | val | bitmask (not actually stored in the db)
----+-----+-----------------------------------------
 1  | AB  | 0100000101 000010
 2  | Ab  | 0100000101 100010

bitmask for where-clause:

0100000101 0

expected selected rows:

 1  | AB

Answer 1

Best I could come up with. It's pretty ugly. No guarantee how fast or well it works.

SELECT HEX(b'0100000101'<< BIT_LENGTH(myCol) - 10) & HEX(myCol) = HEX(b'0100000101'<< BIT_LENGTH(myCol) - 10);

myCol is the col.