MySQL Distinct question

lvollmer
lvollmer used Ask the Experts™
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I have a question about the "distinct" syntax.

In this example:
Select distinct pID, name, address, phone, email from table;

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I only want the distinct pID.

In this query, would my results show distinct values for pID, name, address, phone, and email or JUST pID?
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That query will show all of the distinct rows between all values listed.

If you want to just see the unique PID, you need to just have the columns that you want to be distinct in the select.  If you need to join it back to the source table, you can make it a derived table and join it.

Author

Commented:
Here is my real life query:
SELECT
    pd.person_id, pd.first,pd.email,sod.option_text
FROM
    pd
INNER JOIN
    srf ON pd.person_key = srf.person_key
INNER JOIN
    ON srf.survey_option_key =  sod.survey_option_key
WHERE
    srf.survey_option_key IN (297,298,299)
AND
    srf.survey_question_key = '43'
AND
    pd.is_subscriber ='1'
ORDER BY
    pd.person_id ASC

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This works fine, except that it returns rows multiple times for pd.person_id. I am not sure how to apply what you suggested to make sure ONLY pd.person_id is distinct. Any idea?
This will do an inner join to just the distinct ID list so they only display once.
SELECT
    pd.person_id, pd.first,pd.email,sod.option_text
FROM
    pd
INNER JOIN
    srf ON pd.person_key = srf.person_key
INNER JOIN
    ON srf.survey_option_key =  sod.survey_option_key
INNER JOIN (SELECT DISTINCT Person_id FROM PD) PDList ON pd.Person_ID = PDList.Person_id
WHERE
    srf.survey_option_key IN (297,298,299)
AND
    srf.survey_question_key = '43'
AND
    pd.is_subscriber ='1'
ORDER BY
    pd.person_id ASC

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Author

Commented:
thanks - it is running, so i will report back when finished.
Theo KouwenhovenApplication Consultant

Commented:
Hi lvollmer,

Isn't this enough:

Select  pID, name, address, phone, email from table group by pID, name, address, phone, email

Author

Commented:
Murphey - woudln't that still show multiple rows for one pID?
Application Consultant
Commented:
Assuming that pID = PersonalID
and looking to your select, the combination pID and name  etc will be unique,

If not, it makes no sence to select an pID with a name that (maybe) not belongs to that pID or
is one of many that belongs to that pID.

So if pID is connected to one person, the answer is NO

if a pID is connected to more then one person, the answer is Yes, but is that out put still reliable?

Author

Commented:
I will run it now and test.

In the real query I am running (see second query) the result set will return multiple rows for pd.person_id if they have values for this:

WHERE
    srf.survey_option_key IN (297,298,299)

Author

Commented:
this worked, thank you. I guess I did not understand how GROUP BY worked, and it is perfect for this instance.
Theo KouwenhovenApplication Consultant

Commented:
GROUP BY wil select each record that has a unique group by,
if your tabel contains 2 rows with the same pID for 1 person with 2 adresses, the line is shown twice

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