Oracle is prone to errors. logical comparison of null and''

Oracle is prone to errors. logical comparison of null and ''1. In Varchar2 format,'' is equivalent to null (no memory is allocated ). [SQL] the result of the statement 'aa from dual where ''is null exists in select.
2. logical judgment on null is not allowed in Oracle, and only is and is not can be used. [SQL] select 'has 'aa from dual where null = null; [SQL] select' has 'aa from dual where null <> null; [SQL] select 'has 'aa from dual where 'a' <> null; [SQL] select' has 'aa from dual where 'a' <> ''; the results of these four statements do not exist (note the third and fourth sentences); [SQL] select 'has 'aa from dual where null is null; [SQL] select 'aa from dual where 'aaa' is not null; the results of these two statements exist;