MYSQL Joins where conditions may be null - mysql

Question

I'm having an issue with a query using INNER JOIN.
I have two tables. I need the department name and all three approvers. If any of the approvers are NULL, I need that displayed also.
mysql> desc department;
+-------------------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+----------+------+-----+---------+----------------+
| id | int(8) | NO | PRI | NULL | auto_increment |
| departmentName | tinytext | YES | | NULL | |
| primaryApprover | int(8) | YES | | NULL | |
| secondaryApprover | int(8) | YES | | NULL | |
| tertiaryApprover | int(8) | YES | | NULL | |
+-------------------+----------+------+-----+---------+----------------+
mysql> desc approver;
+------------------+------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------------+------------+------+-----+---------+----------------+
| id | int(8) | NO | PRI | NULL | auto_increment |
| approverName | tinytext | YES | | NULL | |
| approverPosition | tinytext | YES | | NULL | |
| approverLogonId | tinytext | YES | | NULL | |
| approverEmail | tinytext | YES | | NULL | |
| isActive | tinyint(1) | YES | | NULL | |
+------------------+------------+------+-----+---------+----------------+
The following query works, but it does not give me data where the primary or secondary approver are NULL:
SELECT
a.departmentName as DEPARTMENT,
pa.approvername as PRIMARY,
sa.approvername as SECONDARY,
ta.approvername as TERTIARY
FROM
department as a
INNER JOIN
approver pa on a.primaryapprover=pa.id
INNER JOIN
approver sa on a.secondaryapprover = sa.id
INNER JOIN
approver ta on a.tertiaryapprover = ta.id
ORDER BY
a.departmentname;
Using this query, I get this result:
+--------------------------------+---------------------------+---------------------------+------------------------+
| DEPARTMENT | PRIMARY_APPROVER | SECONDARY_APPROVER | TERTIARY_APPROVER |
+--------------------------------+---------------------------+---------------------------+------------------------+
| Facilities | Washburn, Hoban | Cobb, Jayne | Reynolds, Malcomn |
| Personnel / HR | Frye, Kaylee | Serra, Inara | Book, Dariel |
+--------------------------------+---------------------------+---------------------------+------------------------+
2 rows in set (0.00 sec)
but should get this result:
+--------------------------------+---------------------------+---------------------------+------------------------+
| DEPARTMENT | PRIMARY_APPROVER | SECONDARY_APPROVER | TERTIARY_APPROVER |
+--------------------------------+---------------------------+---------------------------+------------------------+
| Business Office | NULL | Rample, Fanty | Niska, Adelei |
| Facilities | Washburn, Hoban | Cobb, Jayne | Reynolds, Malcomn |
| Personnel / HR | Frye, Kaylee | Serra, Inara | Book, Dariel |
| Technical Services | Tam, River | NULL | Tam, Simon |
+--------------------------------+---------------------------+---------------------------+------------------------+
4 rows in set (0.00 sec)
I'm not good at joins to begin with....what am I missing here?

Answer 1

Just use LEFT JOINS
SELECT
a.departmentName as DEPARTMENT,
pa.approvername as PRIMARY,
sa.approvername as SECONDARY,
ta.approvername as TERTIARY
FROM
department as a
LEFT JOIN
approver pa on a.primaryapprover=pa.id
LEFT JOIN
approver sa on a.secondaryapprover = sa.id
LEFT JOIN
approver ta on a.tertiaryapprover = ta.id
ORDER BY
a.departmentname;
INNER JOIN - keeps only records that match from both sides .
LEFT JOIN - keeps all the records from the left table, and only the record matching from the right table.
You can also use COALESCE to replace null values with a default value like '-1' or something.