Understanding NULL in MySQL

NULL is a unique value. It represents a value that is not defined and that is not really equal to BLANK (”).

While using it in queries, we need to use the utmost care.

Here are a few examples in which you might be confused with the output unless you are very comfortable using NULL.

1. When NULL is added to a number, the output is still NULL

Query: SELECT 1 + NULL;

Output:

+-----------+| 1 + NULL  |+-----------+| (NULL)    |+-----------+

2. When used with a string function such as CONCAT

Query: SELECT CONCAT(‘Indigo’,NULL);

Output:

+------------------------+| CONCAT('Indigo',NULL)  |+------------------------+| (NULL)                 |+------------------------+

Alternatively, when the query is SELECT CONCAT(‘Indigo’,’ Nation’);

Output:

+-----------------------------+| CONCAT('Indigo',' Nation')  |+-----------------------------+| Indigo Nation               |+-----------------------------+
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