How to compare NULL values with other significant values

Preamble

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In this article, you will learn how to display NULL values in other meaningful values.

Dr.EFCodd, who is the creator of the relational model for the database, introduced this concept of NULL in the theory of relational databases.

According to Dr.EFCodd, NULL means unknown value or missing information.

MySQL also supports NULL, which represents the concept of missing or inapplicable information.

In the database table, you store data that contain NULL values

When you provide data to users in the form of reports, it makes no sense to show NULL values.

To make reports more readable and understandable, you need to display NULL values in the form of other values, such as unknown, missing, or inaccessible (no data). You can do this by using the IF function.

The syntax of the IF function is as follows:

IF(exp,exp_result1,exp_result2);

If the value of exp is TRUE (when exp <> 0 and exp <> NULL), then IF returns a value from otherwise exp_result1 returns exp_result2.

The IF return can be a string or a number, depending on exp_result1 and exp_result2.

Lets practice with some examples for a better understanding

Below is the partial data in the customer table, which includes the customername state and country:

SELECT
customername, state, country
FROM

ORDER BY country;

Status values are not available for some clients. You can use the IF function to display the NULL value as N/A:

SELECT
customername, IF(state IS NULL, 'N/A', state) state, country
FROM

ORDER BY country;

In addition to the IF function, MySQL provides the IFNULL function, which allows NULL to process values directly. The syntax of the IFNULL function is given below:

IFNULL(exp,exp_result);

The IFNULL function returns the value of the expression exp_result if exp is calculated as NULL, otherwise, it returns the value of exp.

In the next query, the IFNULL function displays NULL as unknown as follows:

SELECT customername,
IFNULL(state, "N/A")state,
country
FROM customers
ORDER BY country;

In this article, you learned how to use IF and IFNULL to display NULL values on other more important values to present data in a readable form.

Important concepts on NULL values

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