Why Does MySQL's CONCAT Return NULL When Fields Contain NULL Values, and How Can I Fix It?

MySQL CONCAT Returns NULL for Fields Containing NULL: Solutions and Alternatives

MySQL's CONCAT function concatenates multiple fields into a single string. However, it can be problematic when some of the fields contain NULL values, resulting in the entire expression returning NULL.

Problem Overview

Consider the following table and query:

Table: devices

| affiliate_name | affiliate_location | model | ip | os_type | os_version |
|---|---|---|---|---|---|
| cs1 | inter | Dell | 10.125.103.25 | Linux | Fedora |
| cs2 | inter | Dell | 10.125.103.26 | Linux | Fedora |
| cs3 | inter | Dell | 10.125.103.27 | NULL | NULL |
| cs4 | inter | Dell | 10.125.103.28 | NULL | NULL |

Query:

SELECT CONCAT(`affiliate_name`,'-',`model`,'-',`ip`,'-',`os_type`,'-',`os_version`) AS device_name
FROM devices

This query returns the device name as follows:

cs1-Dell-10.125.103.25-Linux-Fedora
cs2-Dell-10.125.103.26-Linux-Fedora
(NULL)
(NULL)

Solution: Replace NULL with an Empty String

To ignore NULL values and concatenate empty strings instead, you can use the COALESCE function. COALESCE takes multiple arguments and returns the first non-NULL argument.

Here's the modified query:

SELECT CONCAT(COALESCE(`affiliate_name`,''),'-',COALESCE(`model`,''),'-',COALESCE(`ip`,''),'-',COALESCE(`os_type`,''),'-',COALESCE(`os_version`,'')) AS device_name
FROM devices

This query returns the desired result:

cs1-Dell-10.125.103.25-Linux-Fedora
cs2-Dell-10.125.103.26-Linux-Fedora
cs3-Dell-10.125.103.27-
cs4-Dell-10.125.103.28-

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