问题
I'm replacing a subquery with an self join to improve performance of my query.
The old subquery was like this:
(SELECT fage2.agecat
FROM people AS fage2
WHERE fage2.aacode = people.aacode
AND fage2.persno = 2) AS RAge2,
The new self join is like this:
(SELECT [People].[AgeCat]
FROM [People]
INNER JOIN [People] AS p2
ON [People].[aacode] = [P2].[aacode]
WHERE [P2].[PERSNO] = 2 ) AS RAge2,
but returns a No Current Record error message.
The goal is to find the record that has the same aacode but has the PERSNO number of 2 and return the AgeCat for that record in a column called RAge2,
This is only part of a larger query which is explained in full Convert a SQL subquery into a join when looking at another record in the same table Access 2010
回答1:
Huum, looks like this query that you want to optimize is part of a bigger query, and would be important to the question that you post the entire query so it would help on understanding your problem ...
Also, from what I can see you would be showing the RAge2 for both rows with same AACode not only to the one that has Persno = 2 as you said on the goal. Pasting your entire query would help to understand that also.
I was trying to understand your query, so I created a fake query for your original one:
SELECT
(SELECT FAge2.AgeCat
FROM People AS FAge2
WHERE FAge2.aacode = People.aacode
AND FAge2.PERSNO = 2) AS RAge2,
People.PersonId
FROM People
To get the same results you would need a Left Join and not a Inner Join as a query with a subquery wouldn't exclude results from the outer table, so you would have something like this as the resulting Join query:
SELECT
FAge2.AgeCat as RAge2,
People.PersonID,
FROM People
Left JOIN People AS FAge2 ON (FAge2.aacode = People.aacode AND FAge2.PERSNO = 2)
回答2:
Please use:
(SELECT [People].[AgeCat] FROM [People] INNER JOIN [People] AS P2 ON ([People].[aacode] = [P2].[aacode] AND [P2].[PERSNO] = 2)) AS RAge2
来源：https://stackoverflow.com/questions/8137548/no-current-record-error-in-ms-access-2010-while-using-a-self-join