What Is the Relationship Between an Empty String and NULL?

Answer: Whether an empty string in GaussDB is NULL depends on the compatibility mode of the database.

• A null string is judged as NULL in ORA-compatible mode.

  gaussdb=# CREATE DATABASE db_test1 DBCOMPATIBILITY = 'ORA';
  gaussdb=# \c db_test1
  db_test1=# SELECT '' IS NULL;
   ?column? 
  ----------
   t
  (1 row)

• A null string is not judged as NULL in MySQL-compatible mode.

  gaussdb=# CREATE DATABASE db_test2 DBCOMPATIBILITY = 'MYSQL';
  gaussdb=# \c db_test2
  db_test2=# SELECT '' IS NULL;
   ?column? 
  ----------
   f
  (1 row)