We have a column in the Database that has NULL values in it. When we fetch that column using a SQL/NSQL query those NULL values are not being returned. Why is this?
1. The reason why NULL values would be left out is because of a comparison such as "column != certain_value" condition in the WHERE clause
Example: If we consider the following query, then a condition such as "value2 != 'Expense' " will result in NULL values against value2 column being left out
value2 != 'Expense';
2. Whenever a comparison is made against a column in the WHERE clause, the NULL values do not satisfy either the Truth or the False condition
3. This is a standard behaviour across all RDMS products - Postgres, Oracle etc.
Latest version tested against: 15.9.2
Adding the following additional line in the WHERE clause will fetch the NULL values also.
OR value2 IS NULL
The Example query will therefore be of the following form:
value2 != 'Expense'
value2 IS NULL;