Oracle condition: 1=1 or 1=0, adding conditions dynamically

See the conditions in the WHERE statement: where 1=1 and 1=2 or 1<>1 use: 1=1: is used to add conditions when using and to tie other conditions (dynamic join subsequent conditions) such as: String SQL              = "SELECT * from emp where 1=1";              if (username!=null) sql+= "and username=" +username;     if (password!=null) sql+= "and password=" +password;    1=2 or 1<>1 discards the data in order to get the structure of the table, so that the tables are created with the same fields as the original table, others are not guaranteed to be the same (for example, they can be empty and the original table is different).                For example: CREATE TABLE emp_tmp as SELECT * from EMP where 1=2; Import the data at this time: INSERT INTO emp_tmp select * from EMP;

Oracle condition: 1=1 or 1=0, adding conditions dynamically