How do I fetch query results with multiple criteria? - mysql

Question

I have a table like this
Table
-----
userid
fieldid
fieldvalue
where userid and fieldid are the primary key pair for this table.
I want to make an sql query that finds all users that have fieldvalue equal to something for a selected fieldid
For example, for the values
fieldid: 817
fieldvalue: 'yes'
I can have an sql query like:
select userid FROM table where (fieldid=817 AND fieldvalue='yes')
This query works fine.
However if i have a second or a third criterion, making the query
like this:
select userid
FROM table
where (fieldid=817 AND fieldvalue='yes')
AND (fieldid=818 AND fieldvalue='no')
returns an empty result but the conditions are satisfied in the
individual criterion.
Is there any way to correct this ?
update
i forgot to write down a use case (appologies)
userid, fieldid, fieldvalue
1 , 817, yes
1, 818, no
1, 825, yes
2, 817, yes
2, 818, yes
3, 829, no
for this table i want an sql query that finds the users that have the following conditions satisfied : The fieldid 817 has a value of yes and the fieldid 818 a value of no
Using the OR suggestions i had so far satisfied either the fieldid 817 to have a value of yes OR the fieldid 818 to have a value of no
I want both conditions to be satisfied. In the above the expected result will be
userid
1
and not
userid
1
2
Since userid 2 doesn't satisfy both conditions. Apologies for the confusion.

Answer 1

You should use an OR between your different criteria.
SELECT userid
FROM table
WHERE (fieldid=817 AND fieldvalue='yes')
OR (fieldid=818 AND fieldvalue='no')
The difference between using AND/OR
The AND operator displays a record if both the first condition and the
second condition is true.
The OR operator displays a record if either the first condition or the
second condition is true.
EDIT: Based on your comments you can do it the following way
select t1.userid
FROM temp t1
where (t1.fieldid=817 AND t1.fieldvalue='yes')
AND EXISTS (SELECT userid
FROM temp t
WHERE t.userid = t1.userid
AND fieldid=818
AND fieldvalue='no')
see a sqlfiddle with a working copy
or even this way
select t1.userid
FROM temp t1
left join temp t2
on t1.userid = t2.userid
where (t1.fieldid=817 AND t1.fieldvalue='yes')
AND t2.fieldid=818 AND t2.fieldvalue='no'
here is another sqlfiddle
if you had more fields that you wanted to join on, then you would do the following:
select t1.userid
FROM temp t1
left join temp t2
on t1.userid = t2.userid
left join temp t3
on t1.userid = t3.userid
where (t1.fieldid=817 AND t1.fieldvalue='yes')
AND (t2.fieldid=818 AND t2.fieldvalue='no')
AND (t3.fieldid=819 AND t3.fieldvalue='no')

Answer 2

Try using OR
select userid FROM table where (fieldid=817 AND fieldvalue='yes') OR(fieldid=818 AND fieldvalue='no')
Your query wanted the fieldid to be 817 and 818 which isn't possible.

Answer 3

You should use OR not AND in your WHERE clause. Check out this link for a quick-and-easy explanation.

Answer 4

Hi Please try OR in Place of AND
select userid FROM table where (fieldid=817 AND fieldvalue='yes') OR (fieldid=818 AND fieldvalue='no')
If you use AND then it will check if both conditions fieldid=817 AND fieldvalue='yes' ANd fieldid=818 AND fieldvalue='no' must be fulfilled but it is not possible. ANd when you will use OR operator between both conditions then it will give result having both conditions ..
thanks

Answer 5

you need to use it like:
select userid
FROM table
where fieldid in (817, 818) and fieldvalue in ('yes', 'no');

Answer 6

In addition to the many suggestions of using OR, which are entirely correct, you could also use IN (which might make the query more readable if it scales).
SELECT userid FROM table WHERE (fieldid, fieldvalue) IN (
(817, 'yes'),
(818, 'no' )
);
To find all userid that satisfy both conditions, you need to self-join table to itself:
SELECT userid
FROM table AS t1 JOIN table AS t2 USING (userid)
WHERE
(t1.fieldid = '817' AND t1.fieldvalue = 'yes')
AND (t2.fieldid = '818' AND t2.fieldvalue = 'no' )