Use NULL-related functions in queries

This topic provides specific examples on how to use NULL-related functions to define and convert NULL values.

NULL-related functions are used to handle NULL values. A NULL value cannot be equal or unequal to any numeric value. To determine whether a value is NULL, you can use the IS NULL operator or use the NVL() function to convert a NULL value into a user-defined string.

Examples

Convert a NULL value. In an Oracle tenant, if a column may contain NULL values, you can use the NVL() or NVL2() function to detect and convert the NULL values. Execute the following SQL statements:

1. Create a table named t_null.

   obclient> CREATE TABLE t_null(id number NOT NULL PRIMARY KEY, name varchar(10));
   Query OK, 0 rows affected
   

2. Insert data into the t_null table.

   obclient> INSERT INTO t_null(id, name) values(1,'A'), (2,NULL), (3,'NULL');
   Query OK, 3 rows affected
   Records: 3  Duplicates: 0  Warnings: 0
   

3. Query the t_null table, and use the NVL() or NVL2() function to convert special characters.

   obclient> SELECT id, name, nvl(name, 'NOT APPLICABLE') n_name,
             nvl2(name, 'NOT NULL', 'NOT APPLICABLE') n2_name FROM t_null;
   +----+------+----------------+----------------+
   | ID | NAME | N_NAME         | N2_NAME        |
   +----+------+----------------+----------------+
   |  1 | A    | A              | NOT NULL       |
   |  2 | NULL | NOT APPLICABLE | NOT APPLICABLE |
   |  3 | NULL | NULL           | NOT NULL       |
   +----+------+----------------+----------------+
   3 rows in set