You can use LEFT JOIN
in SQL query.
$query = "SELECT " .
"e.EQUIPMENT_ID, " .
"e.CUSTOMER_ID, " .
"e.DESCRIPTION, " .
"e.LOCATION, " .
"e.JOB_SITE, " .
"e.PROJECT_NAME, " .
"jb.DESCRIPTION AS JOB_SITE_NAME " .
"FROM equipments e " .
"LEFT JOIN jobsites jb ON jb.JOBSITE_ID = e.JOB_SITE " .
"WHERE e.CUSTOMER_ID = 1 ".
"ORDER BY e.EQUIPMENT_ID ASC";
This query will return NULL VALUE
for column JOB_SITE_NAME
if there is no row
matching jb.JOBSITE_ID
in equipments
table