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mysql combine two columns into one in query [closed]

select a.id, a.one, a.two,b.three FROM a
left join b
on b.three=a.one and b.three=a.two
group by a.id


Is this query right?

I want b.three equal a.one and also a.two
a.one and a.two have different values.

b.three

a.one

a.two

a.one

a.two

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on b.three=a.one OR b.three=a.two

GROUP BY

5 Answers
5

Hello As you have mentioned in your question that a.one and a.two have different values and you want to fetch the result where b.three must be equal to a.one and a.two

So your current query will give result only when you have a.one and a.two both same values.
If your data has few similar values for a.one and a.two and that you want to compare with b.three then yes your query is perfectly right but if a.one and a.two will be always different then this query will not work.

If you want to fetch the result where b.three should be either equal to a.one or a.two then you should use Or condition instead of and.

It's better that you first clarify what exactly your requirement is and if possible then you should provide some sample data so others can understand your problem correctly.

I hope this ans will be useful for you.

You have 2 ways of joining by 2 parameters:

SELECT *
FROM t1
JOIN t2 USING (id, date)


or:

JOIN t2 ON (t2.id = t1.id AND t2.date = t1.date)


But the problem is that i haven't made a request with such situation when you need to use 1 table column for both conditions. Just try it and I hope that it'll help you!

i know also if a.one and a.two different values query dont work.
but i want to know how we can combine these columns and then equal to b.three.

it is one part of my real example.if u want i can send main problem.

$con =mysqli_connect('localhost','root','','DB'); if
(!empty($_SERVER['HTTP_CLIENT_IP']))
$ip=$_SERVER['HTTP_CLIENT_IP']; elseif
(!empty($_SERVER['HTTP_X_FORWARDED_FOR']))
$ip=$_SERVER['HTTP_X_FORWARDED_FOR']; else
$ip=$_SERVER['REMOTE_ADDR']; $sql ="SELECT kafsent.id, kafsent.home,
COUNT(likes.ip) as like
FROM kafsent
LEFT JOIN likes
ON likes.post=kafsent.id
GROUP BY kafsent.id"; $query=mysqli_query($con,$sql) ; while($row=mysqli_fetch_assoc($query)) $home =$row['home']; $id =$row['id']; $likes =$row['like']; ?> <a href="index.php?id=<?php echo $id; ?> "> <?php echo $home; ?></a> <?php echo $likes; ?>

<?php ?> <?php if(isset($_GET['id'])) $id= (int)$_GET['id']; $query= "INSERT INTO likes(odd_id,ip)
SELECT '$id', '$ip' FROM kafsent WHERE EXISTS( SELECT id FROM test WHERE id='$id') AND NOT EXISTS( SELECT id FROM likes WHERE ip='$ip' AND odd_id='$id' ) LIMIT 1 ";enter image description here $result=mysqli_query($con,$query); header('Location:index.php');


kafsent table

kafsent table data

like table structure