MYSQL combine and select rows by two reference tables - mysql

Question

I am losing my mind over this problem, research has not helped. Is this an anti-pattern and hard because of that, or is it just me...
The IDEA here is that we have a single table for every material we use, we have multiple storage shelf's in which that material is stored on. Every stocklocation has individual quantities and minimum limits.
What I want to achieve is a single SQL-query that outputs this:
+-------+------+---------------------+----------+-----------------+
| SL_Id | M_Id | TimeCreated | Quantity | MinimumQuantity |
+-------+------+---------------------+----------+-----------------+
| 1 | 2 | 2017-11-02 13:04:18 | 10 | 5 |
| 1 | 3 | NULL | NULL | 15 |
| 1 | 4 | 2017-11-02 15:56:56 | 7 | NULL |
+-------+------+---------------------+----------+-----------------+
This is where I am at the moment....
+-------+------+---------------------+----------+-----------------+
| SL_Id | M_Id | TimeCreated | Quantity | MinimumQuantity |
+-------+------+---------------------+----------+-----------------+
| 1 | 2 | 2017-11-02 13:04:18 | 10 | NULL |
| 1 | 3 | NULL | NULL | 15 |
| 1 | 4 | 2017-11-02 15:56:56 | 7 | NULL |
+-------+------+---------------------+----------+-----------------+
Here are the tables:
Material
+----+-----------+
| Id | OrderCode |
+----+-----------+
| 2 | asdf |
| 3 | 75424 |
| 4 | 45567 |
+----+-----------+
StockLocation
+----+-------+
| Id | Label |
+----+-------+
| 1 | asdf |
+----+-------+
Inventory
+----+------------------+-------------+---------------------+----------+
| Id | StockLocation_Id | Material_Id | TimeCreated | Quantity |
+----+------------------+-------------+---------------------+----------+
| 1 | 1 | 2 | 2017-11-02 13:04:18 | 10 |
| 2 | 1 | 4 | 2017-11-02 15:23:26 | 9 |
| 3 | 1 | 4 | 2017-11-02 15:56:56 | 7 |
+----+------------------+-------------+---------------------+----------+
StockLocationMaterialLimit
+----+------------------+-------------+-----------------+
| Id | StockLocation_Id | Material_Id | MinimumQuantity |
+----+------------------+-------------+-----------------+
| 1 | 1 | 2 | 5 |
| 2 | 1 | 3 | 15 |
+----+------------------+-------------+-----------------+
This is the monster behind failure,
SELECT
SL_Id,
M_Id,
TimeCreated,
Quantity,
MinimumQuantity
FROM (
SELECT
SL.Id AS SL_Id,
M.Id AS M_Id,
I.TimeCreated AS TimeCreated,
I.Quantity AS Quantity,
NULL AS MinimumQuantity
FROM StockLocation SL, Material M
JOIN Inventory I on I.Id = (
SELECT Id FROM Inventory I1 WHERE I1.StockLocation_Id=SL.Id AND I1.Material_Id=M.Id ORDER BY I1.TimeCreated DESC LIMIT 1
)
UNION
SELECT
SL.Id AS SL_Id,
M.Id AS M_Id,
NULL AS TimeCreated,
NULL AS Quantity,
SLML.MinimumQuantity AS MinimumQuantity
FROM StockLocation SL, Material M
JOIN StockLocationMaterialLimit SLML on SLML.Id = (
SELECT Id FROM StockLocationMaterialLimit SLML1 WHERE SLML1.StockLocation_Id=SL.Id AND SLML1.Material_Id=M.Id LIMIT 1
)
) tst GROUP BY SL_Id,M_Id

Answer 1

It turned out to be as easy as adding MAX() on those fields which produced NULL values.
SELECT
M_Id,
SL_Id,
TimeCreated,
MAX(Quantity) AS Quantity,
MAX(MinimumQuantity) AS MinimumQuantity
FROM (
SELECT
M.Id AS M_Id,
SL.Id AS SL_Id,
I.TimeCreated AS TimeCreated,
I.Quantity AS Quantity,
NULL AS MinimumQuantity
FROM StockLocation SL, Material M
INNER JOIN Inventory I on I.Id = (
SELECT Id FROM Inventory I1 WHERE I1.StockLocation_Id=SL.Id AND I1.Material_Id=M.Id ORDER BY I1.TimeCreated DESC LIMIT 1
)
UNION
SELECT
M.Id AS M_Id,
SL.Id AS SL_Id,
NULL AS TimeCreated,
NULL AS Quantity,
SLML.MinimumQuantity AS MinimumQuantity
FROM StockLocation SL, Material M
INNER JOIN StockLocationMaterialLimit SLML on SLML.Id = (
SELECT Id FROM StockLocationMaterialLimit SLML1 WHERE SLML1.StockLocation_Id=SL.Id AND SLML1.Material_Id=M.Id LIMIT 1
)
) tst GROUP BY SL_Id, M_Id;