with previous rows.

The WHERE clause containing expression:
  CONCAT(empty_field1, empty_field2, ..., 'literal constant', ...)
    REGEXP 'regular expression'
may return wrong matches.

Optimization of the CONCAT function has been fixed.



mysql-test/r/func_concat.result:
  Added test case for bug #36488.
mysql-test/t/func_concat.test:
  Added test case for bug #36488.
sql/item_strfunc.cc:
  Fixed bug #36488.
  The Item_func_concat::val_str method is optimized to
  use first non-empty argument of the CONCAT function for in-place
  result accumulation. This optimization is acceptable if that
  first argument is not a constant.
  However, current implementation checks this condition only for
  the first actual argument of the CONCAT function.
  So, the Item_func_concat::val_str method can corrupt values
  of, for example, literal strings by appending random data.
  
  The Item_func_concat::val_str method has been modified to take
  into account the ability to be modified in-place for the first
  non-empty argument.