Trouble with sql query using Access Database

im using Access as the database and im having a problem with the query below. I know the problem is with the email_date field but I dont know how to fix it. The problem is a text field which im trying to make use it as a datefield by using CDATE and compare it to a actual datefield which is causing the problem. Im getting the data mismatch error. In the email_date field if there is nothing, the field consists of '--', else it has 9/21/2011. Any help would be very much appreciated.

 SELECT A.ICAO, A.IATA, A.AIRPORT_NAME, A.CITY, A.COUNTRY, 
 A.REVISED_DATE, A.COMPANY, A.EMAIL_DATE 
 FROM AIRPORT_CHECKLIST A  
 WHERE A.COMPANY = 'company' 
 AND FLAG_DELETE = 'No' 开发者_JAVA技巧
 AND EMAIL_DATE <> '--'
 AND CDATE(REVISED_DATE) > CDATE(EMAIL_DATE)

You can add a nested IIf() expression in the WHERE clause: return False if EMAIL_DATE is "--"; otherwise return True or False depending up the CDate() comparison of the two fields. A row will only be included in the result set if that expression returns True.

SELECT
    A.ICAO,
    A.IATA,
    A.AIRPORT_NAME,
    A.CITY,
    A.REVISED_DATE,
    A.COMPANY,
    A.EMAIL_DATE
FROM
    AIRPORT_CHECKLIST AS A
WHERE
        A.COMPANY='company'
    AND IIf(EMAIL_DATE='--',False,
            IIf(CDATE(REVISED_DATE) > CDATE(EMAIL_DATE),True,False))
    AND A.FLAG_DELETE='No';

Also if both "date" fields were text type, you could store the date values in "yyyy-mm-dd" format and simply compare the text values with no data type mismatch problems.

A.EMAIL_DATE <> '--' AND A.REVISED_DATE > A.EMAIL_DATE

Edit: If FLAG_DELETE is Yes/No type (instead of text type), use a literal False in the comparison.

AND A.FLAG_DELETE=False

The last line filters what ends up in the resultset, but does not prevent the last line from being run on those records. When EMAIL_DATE = '--' the last line causes your type mismatch.

One way to prevent this would be to use a subquery to filter out the empty dates first:

SELECT * FROM 
(SELECT A.ICAO, A.IATA, A.AIRPORT_NAME, A.CITY, A.COUNTRY, 
 A.REVISED_DATE, A.COMPANY, A.EMAIL_DATE 
 FROM SELECTAIRPORT_CHECKLIST A  
 WHERE A.COMPANY = 'company' 
 AND FLAG_DELETE = 'No' 
 AND EMAIL_DATE <> '--')
WHERE CDATE(REVISED_DATE) > CDATE(EMAIL_DATE)

Change the line: AND FLAG_DELETE = 'No' to AND FLAG_DELETE = 0