I have a MS Access 2003 DB with a table containing customers details with over 3000 records on a multiuser system of 15 users. When the user opens the data entry form the focus is set to a field [Post_Code] ready for data input. Once the user has entered the post code data I want access to check to see if it already exists in the database, if not then the user can carry on inputting with no interruption but if a duplicate does exist then I want a pop-up message warning the user to search for the duplicate before continuing with 2 options Option 1 is to not save the data input to the table and open the search function to allow the user to check if this particular customer is already in the table or Option 2 - If the user is happy this is a genuine new customer then to continue entering data.
The table has a primary key called [ID] but duplicates are allowed in the 'POST CODE' field as many properties are covered by 1 post code but I want a warning to remind the user to check rather than inputting a duplicate again which is what has been happening to date.
The table is called CUSTOMERS, The data input form is called SNAG System and the field I want to check is [Post_Code] which is a string value.
I have tried working out the DLookup command and have a little understanding but cant get it right. I have also tried the DCount function but with no success so would prefer to use DLookup
Thank you in advance.