If else condition how to use in select query?

`i want a query in which if and else will use but i do not know how it will use,below is my table structure ,i want result below mentioned after Produce table ,,please help thanks....`
 

>Item Master Table

`item_code	 Item_Name 	 Weight   	UOM 
  1001	       Pen	      44	   unit 
  1002       Computer     42	   unit`
 

Customer Table

` Customer_ID	 Customer_Name	 Contact	Address
     1	           Akhter	      3434  	 3434
     2	           Hussain   	  333	     555`
 
Customer Item Table
 

`Customer_ItemCode	 Customer_ItemName	 Item_code(FK)	Weight 	Customer_ID(FK) 
 2001	                 Pen America	      1	          100	    1`
 
SalesOrder Table
 
` Order_No	 Customer_ID (FK)	Order_Ref	Date 	 
     1           1                 333  	 333	 
     2        	 2	               222	     222`
 
 
 Produce table 
 
` Prod_No Item_Code(FK)	 qty	Order_No (FK)
   10001	 1	          1	        1	 
   10002	 2	          1      	 2	` 
 
when select 10001 record from Produce table then it result like
`(10001,Pen America,1)`
when i select record 10002 then it result like 
`(10002,Computer,1)`
 
Please suggest...thanks 

DECLARE @CustID  as varchar
  select * INTO #tmp55 from SalesOrder where CustomerID IN (select CustomerID from CustomerItem)
  
  select @CustID = CustomerID from #tmp
  		
  
  if @CustID != ''
		select  Customeritem.CIName,Probale.Prdno,ItemMasterFile.BaleSize  from CustomerItem inner join ItemMasterFile on
		ItemMasterFile.Codeitem=CustomerItem.CItem inner join Probale on Probale.Codeitem=ItemMasterFile.CodeItem where Probale.Prdno=1000003
   
   
  else 
select  Probale.Prdno,ItemMasterFile.BaleSize,ItemMasterFile.BaleSize  from ItemMasterFile
		 inner join Probale on Probale.Codeitem=ItemMasterFile.CodeItem where Probale.Prdno=1000003