postgres=# set standard_conforming_strings = off;
SET
postgres=# select 'a\\bcd' as f1;
WARNING:  nonstandard use of \\ in a string literal
LINE 1: select 'a\\bcd' as f1;
               ^
HINT:  Use the escape string syntax for backslashes, e.g., E'\\'.
  f1   
-------
 a\bcd
(1 row)