SQL If-Else logic based on value of one table - sql

Question

I have the following tables:
Production Table
SerialNumber WorkOrderNumber ItemName ItemType
1234 A2234 ASD 1
1234 A2234 ASD-T 2
1111 B2234 ZXC-T 2
WorkOrder Table
WorkOrderNumber ItemName ItemType
B2234 ZXC 1
B2234 ZXC-T 2
B2234 ZXC-C 3
Scenario: User inputs Serial Number, wants to get the item name of itemtype = 1 from either production table or workorder table
Desired Result
User input Serial number 1234 in application:
ItemName : ASD [Found in production table]
User input Serial number 1111 in application:
ItemName : ZXC [Found in workorder table]
Production and Workorder table is heavily simplified for demonstration purposes. The table contains millions of rows each. I need to come up with a performant query to get the item name.
The only solution I have thought of is to do the following
Use stored procedure and write an if-else logic
Check if the item type of the entered serial number is 1. If true, return itemname.
If itemtype is not 1, get the itemname from workorder table with itemtype = 1
But I'm not sure if that's a preferred method for performance and I feel kinda icky about putting business logic in database.
How would one handle this problem elegantly?

Answer 1

Try this:
select top 1 pt.serialNumber,pt.workOrderNumber,
isNull(wt.ItemName,pt.ItemName) as NameToReturn
from prodTable pt
left join worktable wt on pt.WorkOrderNumber=wt.workOrderNumber and wt.itemType=1
where pt.serialNumber = <input>
order by p1.itemType
Not sure I understand all your requirements, but the above should give you a start point. It finds the part in the prodTable and optionally finds a part in the work Item table. The is Null logic assumes that if a type one exists in Work table, it will be used. You might need to tweak this to a case statement if your rules are different (i.e. 1 in prod table should override worktable)