finding records in a table where there is at least one record in a linked table with a date field of no longer than 3 moths from now()

We have a project database in MSACCESS with the following tables: table PROJECTS with of course an ID and project details. table COMMENTS with an ID, a DATE and a comment text field.

COMMENTS is linked to PROJECTS with a one-many relation. (a project can have multip开发者_如何学Pythonle comments)

What I want is a query that selects all projects with at least one comment with a date that is less than 3 months old.

I tried an inner join and got the filter right, but I thought that with the distinctrow or distinct I could filter out the doubles, but msaccess won't accept the syntax.

It's a simple task that in any programming environment would be easy to do, but I just can't get it into a single query...

[update]: I have one little additional question: Only the records with at least one comment show up and we want new projects (with no comments yet) to show up too. I tried adding an

 "OR count(SELECT projectid FROM comments WHERE (( ( comments.commentdate ) BETWEEN Dateadd("m", -3, DATE()) AND DATE()))) =0 

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Since you seems to want distinct Projects but not the associated comment data there are several of ways to accomplish this.

LEFT Join Distinct

SELECT DISTINCT projects.* 
FROM   projects 
       LEFT JOIN comments 
         ON projects.id = comments.projectid 
WHERE  (( ( comments.commentdate ) BETWEEN Dateadd("m", -3, DATE()) AND DATE() ) 
       ) or comments.projectid is null

LEFT Join With Group by

SELECT projects.id, 
   projects.fielda,
   [....]
FROM   projects 
       LEFT JOIN comments 
         ON projects.id = comments.projectid 
WHERE  (( ( comments.commentdate ) BETWEEN Dateadd("m", -3, DATE()) AND DATE() ) 
       ) or comments.projectid is null
GROUP BY 
   projects.id, 
   projects.fielda,
   [....]

IN Clause

SELECT *
FROM   projects 
WHERE  id IN (SELECT projectid
          FROM   comments 
          WHERE  (( ( comments.commentdate ) BETWEEN 
                    Dateadd("m", -3, DATE()) AND DATE() 
                  ))) 

Exists Clause

SELECT * 
FROM   projects 
WHERE  EXISTS (SELECT * 
               FROM   comments 
               WHERE  ( comments.commentdate ) BETWEEN 
                      Dateadd("m", -3, DATE()) AND DATE() 
                      AND ( projects.id = comments.projectid )) 
     OR NOT EXISTS (SELECT * 
               FROM comments
               WHERE projects.id = comments.projectid)

INNER JOIN to an INLINE View With a UNION to a LEFT JOIN

SELECT *
FROM   projects 
INNER JOIN  (SELECT DISTINCT projectid
          FROM   comments 
          WHERE  (( ( comments.commentdate ) BETWEEN 
                    Dateadd("m", -3, DATE()) AND DATE() 
                  ))) comment
     ON projects.id = comment.projectid
UNION ALL 
SELECT * 
FROM projects 
     LEFT JOIN comments
     ON projects.id = comment.projectid 
WHERE  
     comment.projectid is null