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MySQL select and count from multiple tables.

Posted on 2007-04-04
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1,190 Views
Last Modified: 2008-09-08
I have a database structure:
Table: choices
Fields: CID, PID(FK), Choice
Table: voteRecord
Fields: VRID, CID, UID, PID
Table: users
fields: UID, Username
Table: polls
fields: PID, pollQuestion

I wish to select the choice field from choices as well as counting how many times it is in VRID. The closest I have came is:
SELECT choice, count(voteRecord.CID)
FROM choices, voteRecord, users, polls
WHERE choices.PID=2 and voteRecord.UID=users.UID and voteRecord.CID=choices.CID and voteRecord.PID=polls.PID
GROUP BY voteRecord.CID

This provides the answer:
option 1 :: 3
option 2  :: 2
option 3 :: 1
option 4 :: 2

wheras it should be 1:1:1:2 as the number of votes per option.

I want to do this so that even if  for example option one is not selected whenever I go to output the results in java then an empty value is output and it keeps the tables alignd. (this is to be output into tables in a servlet)


Thanks,
Pete
0
Comment
Question by:pete420
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6 Comments
 

Expert Comment

by:cvonrabe
ID: 18854969
I would do something like this:

SELECT choice,
sum(if(voteRecord.CID=1,1,0)) as option_1,
sum(if(voteRecord.CID=2,1,0)) as option_2,
sum(if(voteRecord.CID=3,1,0)) as option_3,
sum(if(voteRecord.CID=4,1,0)) as option_4
FROM choices, voteRecord,users,polls
WHERE choices.PID=2 and voteRecord.UID=users.UID and voteRecord.CID=choices.CID
and voteRecord.PID = polls.PID
GROUP BY voteRecord.CID

Using the above output like:

+--------+----------+----------+----------+----------+
| choice | option_1 | option_2 | option_3 | option_4 |
+--------+----------+----------+----------+----------+
| red      |        3     |        0      |        0      |        0      |
| blue     |        0    |        2       |        0      |        0      |
| pink     |        0    |        0       |        1      |        0      |
| black   |        0    |        0       |        0      |        1      |
+--------+----------+----------+----------+----------+
4 rows in set (0.00 sec)

Of course, you could dynamically build the query.
0
 

Author Comment

by:pete420
ID: 18856579
Hi,

Thanks for the reply. I don't think I have explained it to well tho.

The answer should simply read:
+--------+---------------
|Choice | count(CID)
+--------+---------------
Red               1
Blue               1
Black             1
Green            2

Thanks,
Pete

The number of votes here are just used as an example. It could easily be red: 200, blue 1200, etc etc.
The system is a voting system.
 
0
 
LVL 2

Accepted Solution

by:
taveirne earned 75 total points
ID: 18860189
select c.choice, ifnull(tbl.cnt, 0)
from choices c
left join (
   select cid, count(cid) as cnt
   from voterecord
   where pollid = X
   group by cid
) tbl on tbl.cid = c.cid
0
 

Expert Comment

by:cvonrabe
ID: 18860787
That seems to have done the trick at my end.
0

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