Bizarre Join with comma - sql

Question

I'm looking at someone else's code and find this bizarre join:
SELECT
SUM(
(
intUnitOverheadCost + intUnitLaborCost + intUnitMaterialCost + intUnitSubcontractCost
+ intUnitDutyCost + intUnitFreightCost + intUnitMiscCost
)
*
(
(
CASE
WHEN imtSource = 3
THEN - 1
ELSE 1
END
) * intQuantity
)
)
FROM PartTransactions --imt
INNER JOIN PartTransactionCosts --int
ON imtPartTransactionID = intPartTransactionID
LEFT JOIN Warehouses --imw
ON imtPartWarehouseLocationID = imwWarehouseID
, ProductionProperties --xap <-- weird join
WHERE imtJobID = jmpJobID
AND imtSource IN (2,3)
AND imtReceiptID = ''
AND Upper(imtTableName) <> 'RECEIPTLINES'
AND imtNonInventoryTransaction <= {?CHECKBOXGROUP_4_ShowNonInventory}
AND imtJobType IN (1, 3)
AND imtTransactionDate < DATEADD(d, 1, {?PROMPT_1_TODATE})
AND (
imtNonNettable = 0
OR (
imtNonNettable <> 0
AND ISNULL(imwDoNotIncludeInJobCosts, 0) = 0
)
)
AND intCostType = (
CASE -- Always 1
WHEN xapIMCostingMethod = 1
THEN 1
WHEN xapIMCostingMethod = 2
THEN 2
WHEN xapIMCostingMethod = 3
THEN 3
ELSE 4
END
)
There is only one record in table ProductionProperties and the result of select xapIMCostingMethod from ProductionProperties is always 1.
There are always 4 enumerated results in PartTransactionCosts, but only 1 result is allowed.
ProductionProperties.xapIMCostingMethod is implicitly joining to PartTransactionCosts.intCostType
My specific question is what is really going on with this comma join? It looks like it has to be a cross-join, later filtered in the WHERE clause with one possible result.

Answer 1

Agree with the previous answer. It is a cartesian join but since the rows are 1 it doesn't cause an issue.
I'm thinking if you added rows to ProductionProperties then it would serve as a multiplier for your sum. I did a little experiment to show the issue:
declare #tableMoney table (
unit int,
Product char(5),
xapIMPCostingMethod int,
Cost money
)
declare #tableProdProperties table (
xapIMPCostingMethod int
)
insert #tableMoney (unit, Product, xapIMPCostingMethod, Cost)
values
(1,'bike',1, 2.00),
(1,'car',1, 2.25),
(2,'boat',2, 4.50)
insert #tableProdProperties (xapIMPCostingMethod)
values (1),
(2)
select sum(Cost)
from #tableMoney, #tableProdProperties
I also don't like to use joins where it isn't clear what is joining to what so I always use an alias:
select sum(Cost)
from #tableMoney tbm join #tableProdProperties tpp
on tbm.xapIMPCostingMethod = tpp.xapIMPCostingMethod