In MySQL,

CONCAT('foo', 'bar', NULL) = NULL

Do you need DevOps-experts?

Your development team has a full backlog? No time for infrastructure architecture? Our DevOps team is ready to support you!

• We build reliable cloud solutions with Infrastructure as code
• We are experts in security, Linux and databases
• We support your dev team to perform

Read more Show archive.org snapshot

the NULL always wins in MySQL.

If you would rather treat NULL as an empty string, use CONCAT_WS Show archive.org snapshot (concatenation with separator) instead:

CONCAT_WS('', 'foo', 'bar', NULL) = 'foobar'

PostgreSQL

In PostgreSQL the NULL is not viral in CONCAT:

CONCAT('foo', 'bar', NULL) = 'foobar'