Access SQL join expression is not supported

Question

I'm using access to run a query but it is saying join operation is not supported. I've checked the syntax and it seems fine. Can anyone please help me understand why this is failing:

SELECT
   d.uid,
   md_20180901.monthval,
   md_20180801.monthval,
   md_20180701.val 
FROM
   (
(data as d 
      LEFT JOIN
         (
            SELECT
               md.* 
            FROM
               monthdata md 
            WHERE
               md.monthval = #01/09/2018# 
         )
         as md_20180901 
         ON d.UID = md_20180901.dataUID 
         AND md_20180901.monthval = #01/09/2018# ) 
      LEFT JOIN
         (
            SELECT
               md.* 
            FROM
               monthdata md 
            WHERE
               md.monthval = #01/08/2018# 
         )
         as md_20180801 
         ON d.UID = md_20180801.dataUID 
         AND md_20180801.monthval = #01/08/2018#
   )
   LEFT JOIN
      (
         SELECT
            md.* 
         FROM
            monthdata md 
         WHERE
            md.monthval = #01/07/2018# 
      )
      as md_20180701 
      ON d.UID = md_20180701.dataUID 
      AND md_20180701.monthval = #01/07/2018#
WHERE
   d.UID = "5B51141D";

For context, this is my tables

data table

ID
UID
MYNAME

monthdata table

ID
DATAUID
MONTHVAL
VAL

Answer 1

Access only supports literals in join expressions when the expression has been surrounded by parentheses:

SELECT
   d.uid,
   md_20180901.monthval,
   md_20180801.monthval,
   md_20180701.val 
FROM
   (
(data as d 
      LEFT JOIN
         (
            SELECT
               md.* 
            FROM
               monthdata md 
            WHERE
               md.monthval = #01/09/2018# 
         )
         as md_20180901 
         ON (d.UID = md_20180901.dataUID 
         AND md_20180901.monthval = #01/09/2018#) ) 
      LEFT JOIN
         (
            SELECT
               md.* 
            FROM
               monthdata md 
            WHERE
               md.monthval = #01/08/2018# 
         )
         as md_20180801 
         ON (d.UID = md_20180801.dataUID 
         AND md_20180801.monthval = #01/08/2018#)
   )
   LEFT JOIN
      (
         SELECT
            md.* 
         FROM
            monthdata md 
         WHERE
            md.monthval = #01/07/2018# 
      )
      as md_20180701 
      ON (d.UID = md_20180701.dataUID 
      AND md_20180701.monthval = #01/07/2018#)
WHERE
   d.UID = "5B51141D";

However, you're doing something weird here. You're also comparing inside subqueries. Remove those:

SELECT
   d.uid,
   md_20180901.monthval,
   md_20180801.monthval,
   md_20180701.val 
FROM
(
(data as d 
      LEFT JOIN
         monthdata as md_20180901 
         ON (d.UID = md_20180901.dataUID 
         AND md_20180901.monthval = #01/09/2018#) ) 
      LEFT JOIN
         monthdata as md_20180801 
         ON (d.UID = md_20180801.dataUID 
         AND md_20180801.monthval = #01/08/2018#)
   )
   LEFT JOIN
      monthdata as md_20180701 
      ON (d.UID = md_20180701.dataUID 
      AND md_20180701.monthval = #01/07/2018#)
WHERE
   d.UID = "5B51141D";

Answer 2

Start by removing all the unnecessary parts and making it simpler. Example:

            SELECT
               md.* 
            FROM
               monthdata md 
            WHERE
               md.monthval = #01/09/2018# 
         )
         as md_20180901 
         ON d.UID = md_20180901.dataUID 
         AND md_20180901.monthval = #01/09/2018#

can be simplified:

(SELECT val FROM monthdata WHERE monthval=#01/09/2018#) md_20180901
ON d.UID=md_20180901.dataUID

You do not need to repeat table names unless there is a field name conflict. You do not need to assign aliases that will never be used (in fact I generally only assign aliases if I am using the same table twice). You do not need to add monthval on filtering on the ON since you are already doing it in WHERE . The only field you are actually collecting is val ( monthval is effectively a fixed value since you are filtering by a specific date) so don't use * .

Clean up your query and try adding one monthval at a time and see what happens.