C:\Users\zen>sqlplus hr/hrSQL*Plus: Release 11.2.0.1.0 Production on Fri Mar 31 10:30:32 2017Copyright (c) 1982, 2010, Oracle.  All rights reserved.Connected to:Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit ProductionWith the Partitioning, OLAP, Data Mining and Real Application Testing optionsSQL> create table test_null(id_ number,name_ varchar2(10));Table created.SQL> insert into test_null values(1,‘oracle‘);1 row created.SQL> insert into test_null values(2,‘‘);1 row created.SQL> insert into test_null values(3,null);1 row created.SQL> select * from test_null;       ID_ NAME_---------- ----------         1 oracle         2         3SQL> select nvl(name_,‘It is null‘) nvl_null,nvl(‘‘,‘It is empty string‘) emptystr from test_null;NVL_NULL   EMPTYSTR---------- ------------------oracle     It is empty stringIt is null It is empty stringIt is null It is empty stringSQL> select * from test_null where name_ is null;       ID_ NAME_---------- ----------         2         3SQL> select * from test_null where name_=‘‘;no rows selectedSQL> select * from test_null where cast(name_ as varchar2(10))=‘‘;no rows selectedSQL> select * from test_null where cast(name_ as varchar2(10))=cast(‘‘ as varchar2(10));no rows selectedSQL> select * from test_null where name_<>‘‘;no rows selected

SQL> select * from test_null where nvl(name_,‘‘)=‘‘;

no rows selected

SQL> select * from test_null where nvl(name_,‘A‘)=‘A‘;

ID_ NAME_
---------- ----------
2
3

SQL>

C:\Users\zen>mysql -uzen -pEnter password: ****Welcome to the MySQL monitor.  Commands end with ; or \g.Your MySQL connection id is 1Server version: 5.6.24-log MySQL Community Server (GPL)Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement.mysql> use product_test;Database changedmysql> drop table test_null;Query OK, 0 rows affected (0.37 sec)mysql> create table test_null(id_ int,name_ varchar(127));Query OK, 0 rows affected (0.59 sec)mysql> insert into test_null values(1,‘oracle‘),(2,‘‘),(3,null);Query OK, 3 rows affected (0.08 sec)Records: 3  Duplicates: 0  Warnings: 0mysql> select * from test_null;+------+--------+| id_  | name_  |+------+--------+|    1 | oracle ||    2 |        ||    3 | NULL   |+------+--------+3 rows in set (0.00 sec)mysql> select * from test_null where name_ is null;+------+-------+| id_  | name_ |+------+-------+|    3 | NULL  |+------+-------+1 row in set (0.06 sec)mysql> select * from test_null where name_=‘‘;+------+-------+| id_  | name_ |+------+-------+|    2 |       |+------+-------+1 row in set (0.00 sec)mysql> select * from test_null where name_<>‘‘;+------+--------+| id_  | name_  |+------+--------+|    1 | oracle |+------+--------+1 row in set (0.00 sec)mysql> select * from test_null where name_ is not null;+------+--------+| id_  | name_  |+------+--------+|    1 | oracle ||    2 |        |+------+--------+2 rows in set (0.00 sec)mysql>