sql server - T-SQL Case Then Else Command inside Join -

I have to tell that I am just learning SQL. My job is to validate a report generated by T-SQL written by a consultant who used to work for our company. Can anyone tell me what the following section is doing? I understand the idea of ​​joining an upper part, but I do not understand how the case statement evaluates. The shipment title has been omitted from

, when the shipment is done by the RSLDNM & lt; & Gt; 0 Then 0 other shipment quality SDSHPN & = ShipmentCast FHSHPN and Shipment Quality Rsldnm = shipment cost FHLDNM

I think the expression runs without any errors, but again, my job is not to run SQL, only to validate each step of the code. Thank you in advance and please forgive my inexperience.

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This means that if shipment is not RSLDDM 0, then use 0, otherwise, Use shipment. SDSHPN