I want to stop my Primary Key from repeating.

[crosswire]

Try a break point at this line and then 'step forward' you need to see what sql contains after it executs. Also modify the line to this.
sql = "select [stock code] from stock where [stock code] = " & txt.code

'sql may have txt.code if one exist plus other data, or it may be empty if no txt.code exists, not guaranteed
'then do this (pardon the C++ style)
if(sql == txt.code)
'txt.code exist
else
'txt.code does not exist
endif

[Dj Still]

this is wat i did crosswire

Dim sql As String
Dim text As String
text = txtcode.text
sql = "select [stock code] from stock where [stock code] = '%" & text & "%'"
If sql = txtcode.text Then
MsgBox "Stock Code Already Exit"
Else
MsgBox "Stock Code Ok"
End If
it doesnt work so im woundering if the codeing is correct.

i think ur way could work

[crosswire]

if it does not exists in the database then sql may literally equal "no value was found" and if it exists then sql may equal "one row found\ntextbox" MessageBox sql and see

[crosswire]

You were correct to have
sql = "select [stock code] from stock where [stock code] = '%" & text & "%'"
in principle, but I think there is a syntax error. LIKE is missing with wildcards.

Syntaxwise,
sql = "select [stock code] from stock where [stock code] LIKE '%" & text & "%'"

[CyberCat]

Dim sql As String
Dim text As String
text = txtcode.text
sql = "select [stock code] from stock where [stock code] = '%" & txtcode.text & "%'"

adodc1.recordsource = sql
adodc1.refresh

If adodc1.[stock code] = txtcode.text Then
MsgBox "Stock Code Already Exit"
Else
MsgBox "Stock Code Ok"
'submit record
End If

[crosswire]

I still feel that you need the LIKE or else the wildcards are not recognized as wild cards instead as literals, but it all depends on the data provider and the specific syntax it requires.

ANALYSIS:
You can see the use of the percent sign (%) in the statement after LIKE. When used inside a LIKE expression, % is a wildcard.

http://www8.silversand.net/techdoc/teachsql/ch03.htm
I have not tested the LIKE yet, but when I do I will correct my assumption