Can we use Selection Criteria Screen to tell Query which SQL script to run?

Question

Dear All,
When I run this code, it gives me the screen below:
declare @ScanOp4 nvarchar (30)
set @ScanOp4=
/*select T3.U_ScanOp4 from [dbo].[@SCANNING] T3 where T3.U_ScanOp4*/ '[%0]'
I have used Tools -> Customization to define a UDT and UDF
Query - Selection Criteria
Invoice / Credit Note?            [----------------- ]
                                 (there's a drop-down arrow with 2 choices:
                                  Inv = Invoice
                                  CN  = Credit Note
[OK]       [Cancel]
Now, I have 2 very similar queries; the only difference is that they use different tables because one is for
Purchases (OPCH/PCH1), and the other is for Credit Memos (ORPC/RPC1)
I want to put the above declaration together with my 2 queries all in a single query so that:
(a) If I select 'Invoice', the Invoice part is executed and only invoices are displayed,
(b) If I select 'Credit Note', the Credit Note part is executed and only Credit Notes are displayed.
Do you think such a Query is possible? If yes, please give me an idea how I can achieve it.
I don't want to use UNION ALL because one of my fields is a LINK field to which I have linked all PDF Scanned documents.
I want to preserve the links, since this is the reason I'm writing the query.
Thanks
Leon Lai
Here are my skeleton codes
1st Query: User selects 'Invoice' -
SELECT
T0.[TaxDate] AS 'Doc Dt',
T5.[TransType] AS 'Txn Type',
T0.[DocNum] AS 'Doc No.',
T0.[DocTotal] AS 'Amount'
FROM [dbo].[OPCH] T0
INNER JOIN [dbo].[PCH1] T1 ON T0.[DocEntry] = T1.[DocEntry]
INNER JOIN [dbo].[OJDT] T5 ON T0.[TransID]  = T5.[TransID]
2nd Query: User selects 'Credit Note' -
SELECT
T0.[TaxDate] AS 'Doc Dt',
T5.[TransType] AS 'Txn Type',
T0.[DocNum] AS 'Doc No.',
T0.[DocTotal] AS 'Amount'
FROM [dbo].[ORPC] T0
INNER JOIN [dbo].[RPC1] T1 ON T0.[DocEntry] = T1.[DocEntry]
INNER JOIN [dbo].[OJDT] T5 ON T0.[TransID]  = T5.[TransID]

Answer 1

Try this:
declare @ScanOp4 nvarchar (30)
set @ScanOp4=
/*select T3.U_ScanOp4 from [dbo].[@SCANNING] T3 where T3.U_ScanOp4*/ '[%0]'
If @ScanOp4='Inv'
SELECT
T0.[TaxDate] AS 'Doc Dt',
T5.[TransType] AS 'Txn Type',
T0.[DocNum] AS 'Doc No.',
T0.[DocTotal] AS 'Amount'
FROM [dbo].[OPCH] T0
INNER JOIN [dbo].[PCH1] T1 ON T0.[DocEntry] = T1.[DocEntry]
INNER JOIN [dbo].[OJDT] T5 ON T0.[TransID]  = T5.[TransID]
If @ScanOp4='CN'
SELECT
T0.[TaxDate] AS 'Doc Dt',
T5.[TransType] AS 'Txn Type',
T0.[DocNum] AS 'Doc No.',
T0.[DocTotal] AS 'Amount'
FROM [dbo].[ORPC] T0
INNER JOIN [dbo].[RPC1] T1 ON T0.[DocEntry] = T1.[DocEntry]
INNER JOIN [dbo].[OJDT] T5 ON T0.[TransID]  = T5.[TransID]