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SQL query question

Thread began 4/30/2015 7:53 am by iain331081 | Last modified 4/30/2015 9:47 pm by Ray Borduin | 377 views | 2 replies |

iain331081

SQL query question

Hopefully the solution to this is less complicated than it sounds - its just difficult to summarise without writing it down.

I have a main table, Lodges, and the related table Lodge_Updates. There are two other tables related to the main Lodges table - Countries and Lodge_Likes. Lodge_Likes just has a couple of fields - LodgeIDPL and UserPL - it narrows down the list to a list of Lodges that a particular user has liked.

And from that I would like to return a list of lodges that includes the Date_Updated field from the Lodge_Updates table, where that is the date of the most recent update.

So for example, if I have these records in my Lodges table:

LodgeID, Lodge
1, Lodge A
2, Lodge B
3, Lodge C

And these records in my product updates table:

UpdateID, LodgeID, Update, Date_Updated
1, 1, Update A, 18 April 2015
2, 1, Update B, 1 April 2015
3, 2, Update C, 5 April 2015
4, 2, Update D, 15 April 2015
5, 3, Update E, 10 April 2015
6, 3, Update F, 30 April 2015

I would like to return the following list:

LodgeID, Lodge, Date_Updated
3, Lodge C, 30 April 2015
1, Lodge A, 18 April 2015
2, Lodge B, 15 April 2015

So I nearly have it with:

SELECT DISTINCT UpdateID, Lodges.LodgeID, Lodge, Update, Date_Updated 
FROM Lodges
INNER JOIN Countries ON Lodges.CountryID = Countries.CountryID
INNER JOIN Lodge_Likes ON Lodges.LodgeID = Lodge_Likes.LodgeIDPL
LEFT JOIN Lodge_Updates ON Lodges.LodgeID = Lodge_Updates.LodgeID
WHERE Lodge_Likes.UserIDPL = 123
GROUP BY LodgeID
ORDER BY Date_Updated DESC



But that gives me the list based on the oldest update for any lodge date, not the most recent:

UpdateID, LodgeID, Lodge, Date_Updated
5, 3, Lodge C, 10 April 2015
3, 2, Lodge B, 5 April 2015
2, 1, Lodge A, 1 April 2015

If I change the ORDER BY to:

ORDER BY Date_Updated ASC

That just reverses that order:

UpdateID, LodgeID, Lodge, Date_Updated
2, 1, Lodge A, 1 April 2015
3, 2, Lodge B, 5 April 2015
5, 3, Lodge C, 10 April 2015

Hope that makes sense and is possible somehow.

Thanks.

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Ray BorduinWebAssist

Use:

SELECT UpdateID, Lodges.LodgeID, Lodge, Update, MAX(Date_Updated) AS Date_Updated

MAX() will ensure you get the most recent date... you don't need DISTINCT because you already have GROUP BY LodgeID which will ensure a unique LodgeID for each row.

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iain331081

Thanks Ray - haven't had to use MAX before, but is perfect here.

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