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SELECT, DISTINCT, and JOIN
Posted by: Peter Pham ()
Date: August 28, 2013 02:37PM

Table "myInfo" has columns:
1. id (PK)
2. key
3. value
4. metaId

Table "meta" has columns:
1. id (PK)
2. metaName
3. metaValue
4. instanceNum

metaId in the "myInfo" table correlates to a instanceNum in the "meta" table. The value of the "value" column changes sometimes over different rows with the metaId. Think of the metaId as a link to a timestamp value in the "meta" table("timestamp" and its value would go into the metaName and metaValue columns respectively).

I want to select the distinct values of the 'value' column in "myInfo". So far I have:
SELECT DISTINCT mi.key, mi.value FROM myInfo as mi JOIN metadata as meta
WHERE mi.metaId=meta.instanceNum AND meta.key = 'timestamp' AND mi.value='maxWeight';

But I ALSO want the timestamps associated with those values. So I want the output to look something like:

key value timestamp
maxWeight 10 tons 15:00:05 2011-01-01
maxWeight 5 tons 08:00:07 2011-10-12
maxWeight 25 tons 13:05:09 2013-08-01

I can't place timestamp as one of the columns in my SELECT because then it will return duplicate mi.attrValue values too since the timestamp makes every row unique. I tried putting the DISTINCT keyword behind only mi.attrValue but I got a MySQL error.



Edited 2 time(s). Last edit at 08/28/2013 03:45PM by Peter Pham.

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Subject Written By Posted
SELECT, DISTINCT, and JOIN Peter Pham 08/28/2013 02:37PM
Re: SELECT, DISTINCT, and JOIN Peter Brawley 08/28/2013 04:22PM


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