Syntax:
&

Bitwise AND.

The result type depends on whether the arguments are evaluated as
binary strings or numbers:

o Binary-string evaluation occurs when the arguments have a binary
  string type, and at least one of them is not a hexadecimal literal,
  bit literal, or NULL literal. Numeric evaluation occurs otherwise,
  with argument conversion to unsigned 64-bit integers as necessary.

o Binary-string evaluation produces a binary string of the same length
  as the arguments. If the arguments have unequal lengths, an
  ER_INVALID_BITWISE_OPERANDS_SIZE error occurs. Numeric evaluation
  produces an unsigned 64-bit integer.

For more information, see the introductory discussion in this section.

URL: https://dev.mysql.com/doc/refman/8.0/en/bit-functions.html

