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Best way to query database.  One-to-one query

Posted on 2011-02-25
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Last Modified: 2012-05-11
Hello All,

I have the following (working) query for my website that I have included in the code section.

What I want to achieve from the query:
Take all rows from table 'takers' with completed=1 and quiz_ID=30
Use the user_id on each selected row from 'takers' and select the SINGLE ROW to get matching username from 'users' table
Use the personality_result (which is an ID) to select the matching SINGLE ROW from the 'personalities' table

I stumbled across the syntax that I have used, where you just comma seperate the table names (FROM takers, users, personalities) and then match one row with another (WHERE takers.user_id = users.user_id).

Should I be using a join, or is this the right way to do it if it's just selecting a row in a one-to-one fashion?

But for some reason this doesn't feel right... am I missing something?

Thanks again,

Luke
SELECT taker_ID, takers.user_id, taker_name, start_time, percentage_score, personality_result, users.username, personality_name
FROM takers, users, personalities
WHERE takers.user_id = users.user_id
AND takers.personality_result = personalities.personality_ID
AND completed='1'
AND takers.quiz_ID='30'

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Question by:stellaartois
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4 Comments
 
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Expert Comment

by:mankowitz
ID: 34980222
when you do a select with multiple table names and specify the correlations in a WHERE clause, you are doing an implicit inner join.

To answer your question "should I use a join?", you ARE using a join. You don't need to use the JOIN keyword unless you want a different kind of join (e.g. LEFT OUTER JOIN)

Also, if you want a single line, you may need to specify "LIMIT 1"
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Author Comment

by:stellaartois
ID: 34980417
Thanks Manowitz for the response.

From what I have read, it seems that I want to use the explicit inner join notation to ensure that only those with matching results exist.

I am struggling to put this query in to the explicit syntax because there are 3 tables involved.

Do you happen to know how I would rewrite this query to be in the explicit notation?

Thanks again,

Luke
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LVL 24

Accepted Solution

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mankowitz earned 250 total points
ID: 34980804
SELECT taker_ID, takers.user_id, taker_name, start_time, percentage_score, personality_result, users.username, personality_name
FROM takers,
LEFT INNER JOIN users ON (takers.user_id = users.user_id)
LEFT INNER JOIN personalities ON (takers.personality_result = personalities.personality_ID)
WHERE
completed='1'
AND takers.quiz_ID='30'
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Author Closing Comment

by:stellaartois
ID: 34987584
Perfect, thanks for clearning up in my mind how to do a join of more than one table
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