Syntax:
BIT_XOR(expr)

Returns the bitwise XOR of all bits in expr. The calculation is
performed with 64-bit (BIGINT) precision.

If there are no matching rows, BIT_XOR() returns a neutral value (all
bits set to 0).

URL: https://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html

