Checking Null values and Not null values in foxpro9

Question

I got some fields from SQL server into my Foxpro cursor as below.

stra="SELECT  cCm_Sgl_TaxInv,cInvNo FROM MIS.dbo.vInvFinalAll where cInvNo=?thisform.txtInvoiceNo.value"

SQLEXEC(hndOps,stra,'TaxInv')

And I need to check null values and not null values using IF condition. I wrote the following code and it does not give the expected result.

SELECT TaxInv
IF NOT ISNULL(cCm_Sgl_TaxInv)
ELSE
ISNULL(cCm_Sgl_TaxInv)
thisform.cmdCreate.Enabled = .T. 
MESSAGEBOX("The value is already inserted")
endif

How can I do this?

Answer 1

It is not very clear what you are asking here, checking your code, probably this is what you meant:

IF ISNULL(TaxInv.cCm_Sgl_TaxInv)
   thisform.cmdCreate.Enabled = .T. 
   MESSAGEBOX("The value is already inserted")
endif

EDIT: This could be simpler for what you are trying to do:

text to m.stra noshow

SELECT case when cCm_Sgl_TaxInv is null then 1 else 0 end as txStatus
FROM MIS.dbo.vInvFinalAll 
where cInvNo=?thisform.txtInvoiceNo.value

endtext
SQLEXEC(m.hndOps,m.stra,'TaxInv')

if (TaxInv.txStatus = 1)
       thisform.cmdCreate.Enabled = .T. 
       MESSAGEBOX("The value is already inserted")
endif