Is it possible to select x random rows from a table, where one of the rows have to be a special row (thereby with a special field value) within one query?
Basically what I'm trying to create is a Guessing Game, where you have x amount of questions, with x amount of possible (checkbox selectable) answers!
This is how I select the answers currently... With 2 query's
$answers = 4; // This is the max amount of answers
// Just for testing the question_id is manually set
$query = "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` != 1 ORDER BY RAND() LIMIT " . ($answers - 1) . "";
$query = "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` = 1 LIMIT 1";
The "question_id" tells which question we are talking about, and the "correct" just tells if that field is the correct answer
So is it possible to select x random rows from a table, where one of the rows have to be "the correct one", within one query?
may be use UNION ?
$answers = 4;
$query = "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` != 1 ORDER BY RAND() LIMIT " . ($answers - 1) . "";
$query .= " UNION ";
$query .= "SELECT * FROM `answers` WHERE `question_id` = 0 AND `correct` = 1 LIMIT 1";
With one single query, you will be able to get the desired result
http://dev.mysql.com/doc/refman/5.0/en/union.html
$query = "SELECT * FROM answers WHERE ... whatever ... AND `question_id` IN (5, 9, 12, 16, 2)
So, you first find the number of rows and then put the correct answer's ID in to the WHERE IN statement. Because you know the one you want, you can just surround it with random IDs from the table and then render them in a random fashion.
Related
I am trying to add a "Related Products" section below my product. I can only get this to work if
I use two separate SELECTS. I am trying to combine them but can't get it to work.
Same Table in MySQL -
<?php
//select items from db
$items = mysql_query
("SELECT * FROM table WHERE (myinvno='dg300')
OR (action='alive' AND cate='dogs'
ORDER BY productNo ASC LIMIT 0, 4)");
or die(mysql_error());
while($item = mysql_fetch_array($items))
{
?>
This part is for the Related Products section:
OR (action='alive' AND cate='dogs'
ORDER BY productNo ASC LIMIT 0, 4)");
Thank you ~
The correct syntax would look like:
$items = mysql_query("
SELECT *
FROM table
WHERE (myinvno = 'dg300') OR
(action = 'alive' AND cate = 'dogs')
ORDER BY productNo ASC
LIMIT 0, 4"
);
You were missing a closing parent after 'dogs'.
EDIT:
Hmmm . . . I wonder if this is what you want:
SELECT *
FROM table
WHERE (myinvno = 'dg300')
UNION ALL
(SELECT *
FROM table
WHERE (myinvno <> 'dg300') AND
(action = 'alive' AND cate = 'dogs')
ORDER BY productNo ASC
LIMIT 0, 4
);
This gets all rows that match the first condition plus four more that match the second.
Suppose I have a table TABLE:
NAME ID ...
m -1 ...
f -1 ...
g -1 ...
b -1 ...
z -1 ...
And I want to turn it into:
NAME ID ...
f 1 ...
g 2 ...
m 3 ...
b -1 ...
z -1 ...
You probably get the idea:
select the first 3 rows from the original table (preserving order)
order selected rows by the NAME column.
update selected rows' IDs with their position in the new table (keeping the remaining unselected rows in their original positions).
So (m, f, g) got sorted to (f, g, m) and (b, z) remained (b, z).
Here's how I am trying to do it in PHP:
$count = 0;
$query = "UPDATE TABLE SET ID = $count:= $count + 1 ORDER by NAME DESC LIMIT 3";
mysqli_query($con, $query);
But I don't think I can just go ahead and increment a counter and store its value like that. Any advice?
You can try this :
$limit = 3;
for($count = 0 ; $count < $limit;$count++ ){
$query = "UPDATE TABLE SET ID = $count + 1 WHERE ID = '-1' ORDER by NAME DESC";
mysqli_query($con, $query);
}
$query = "UPDATE TABLE SET ID = '-1' WHERE ID > $limit ORDER by NAME DESC";
mysqli_query($con, $query);
In the above logic :
In the final loop, all the IDs are set to $limit
However the update command outisde the loop will set back IDs to -1 again
First, you can quickly query for the first 3 rows in the table and get the name property only and assign the value in an array.
$sql = "select name from table order by name limit 3"
$query = $mysqli->query($sql);
Now let's construct a helper array:
while ($row = $mysqli->fetch_assoc()) {
$a[] = $row['name'];
}
Now just structure the queries:
foreach($a as $id => $name) {
$query = "update table set id={$id+1} where name='$name' limit 1";
// execute the query
}
Note that I assume that the name is unique so I added the limit 1 directive to tell it stop looking for rows to update once it has found a row.
Also, don't forget that array keys are counting starting from 0, hence we are adding 1 to the $id in the loop.
There may be more elegant solutions but this one is rather easy to understand and use.
In MySQL:
SET #row_number = 0;
update TABLE d
join
(
select
NAME,
#row_number:=#row_number+1 as ID,
from
(select NAME from TABLE limit 3) t
order by
NAME asc
) s on s.NAME = d.NAME
set d.ID = s.ID;
SQLFiddle: http://sqlfiddle.com/#!9/dffecf/1
This assumes NAME is your unique key, otherwise likely best to replace with an Identity column in your table and use that for the update.
This approach may require some syntax changes depending on your DB engine. By doing this in SQL, we only make one pass at the DB. Not a huge deal to iterate in multiple passes with PHP if you're only updating three records, but if it was a 1000, etc.
I am trying to display questions, along with the users answer in a specific order, NOT ASC or DESC, but as defined by the "question_order" column.
I have the following tables in a mysql db:
questions (qid, question_text)
answers (aid, uid, answer)
usermeta (userid, question_order)
"questions" table contains the questions
"answers" table contains every users answers to all questions
"usermeta" table contains the sort order for the questions in "question_order".
"question_order" is unique per user and is in the db as a pipe delimited list. (i.e.: 85|41|58|67|21|8|91|62,etc.)
PHP Version 5.3.27
If this entire procedure can be better accomplished using a completely different method, then please let me know.
My PHP ability is limited. With that said, below is what I have at the moment after several hours of playing ...
$sql = "
SELECT
*
FROM
".USERMETA_TABLE."
WHERE
userid = {$userid}
";
$result = $db->query($sql) OR sql_error($db->error.'<br />'.$sql);
$row = $result->fetch_assoc();
$order_array = explode('|', $row['question_order']);
$sql = "
SELECT
*
FROM
".QUESTIONS_TABLE."
";
$result = $db->query($sql) OR sql_error($db->error.'<br />'.$sql);
$row = $result->fetch_assoc();
// my attempt at sorting the questions. the $order_array
// does not have a unique id so I am kind of lost as to
// how to make this work
usort($myArray, function($order_array, $row) {
return $order_array - $row['qid'];
});
$sql = "
SELECT
*
FROM
".QUESTIONS_TABLE."
";
$result = $db->query($sql) OR sql_error($db->error.'<br />'.$sql);
while ( $row = $result->fetch_assoc() )
{
$sql = "
SELECT
*
FROM
".ANSWERS_TABLE."
WHERE
uid = {$userid}
AND
qid = ".$row['qid']."
LIMIT
1
";
$result2 = $db->query($sql) OR sql_error($db->error.'<br />'.$sql);
$row2 = $result2->fetch_assoc();
echo ' <p>'.$row['question_text'].'</p>'."\n";
echo ' <p>'.$row2['answer'].'</p>'."\n";
}
Filter out the data when retrieving from db.
Use:- SELECT * FROM [TABLE_NAME] ORDER BY qid DESC
Then in PHP you can use session variables and modify the values accordingly.
If you want to order using ID you can use
SELECT * FROM [TABLE_NAME] ORDER BY qid DESC
this will order in descending order If you want in ascending order use ASC
I went ahead and altered the DB by adding a table to store the question numbers, user sort order, and student user id:
student_id, sort_order, question_id
1 1 8
1 2 2
1 3 97
and then was able to select it all with the following statement:
SELECT q.*
FROM
questions q
JOIN questions_sorting_order qso
ON q.id = qso.question_id
ORDER BY qso.sort_order
WHERE qso.student_id = $student_id
...works great.
Thanks to FuzzyTree for his help on this at: How do I sort data from a mysql db according to a unique and predetermined order, NOT asc or desc
I've been looking for this for a while but with no success.
I am trying to implement a recomendation bar, for example like in youtube, when you are seeing a video it shows the list or recommended videos on the right.
At this moment I am using this method:
$offset_result = mysql_query( " SELECT FLOOR(RAND() * COUNT(*)) AS `offset` FROM `$tablename` ");
$offset_row = mysql_fetch_object($offset_result );
$offset = $offset_row->offset;
$result_rand = mysql_query( " SELECT * FROM `$tablename` LIMIT $offset, 9 " );
This works fine, but sometimes doesn't show any result, and the problem is also that its not completely random, because it shows for example the first ID as 200, so the next result will be id 201 and then 202 and so.
I would like to know if there is a way to show this 9 randon results, for example 1º result id 500, 2º result id 10, 3º result id 788, etc etc?
Thank you
Not entirely sure this answers what you are looking for, but try:
$result_rand = mysql_query("SELECT * FROM " . $tablename . " ORDER BY RAND() LIMIT 9");
You can use php rand() function to create 5 numbers and save them in an array:
http://php.net/manual/en/function.rand.php
<?php
$rand_array = array();
for($i=1;$i<5;$i++) {
$rand_array[$i] = rand(0,500);
}
?>
and after that create a query with every int with a foreach loop and work with your data.
<?php
foreach ($rand_array as $integer) {
$q = "SELECT * from $tablename WHERE id='$integer';";
}
?>
Does this helps?
First you should use mysqli_ functions instead of mysql_ because the latter is deprecated. Second use order by rand() to get random rows:
$rand_result = mysqli_query( "SELECT * FROM $tablename ORDER BY RAND() LIMIT 9;" );
UNTESTED:
SELECT id, #rownum:=#rownum+1 AS rownum, name
FROM users u,
(SELECT #rownum:=0) r
THis will give a unique number to each row in sequence. Now if you create a temp table with 9 random numbers between 1 and count(*) of your table and JOIN those two together...
Not sure about performance but seems like it might be faster than Rand and order by since I only need 9 random numbers
I have problem with database. I want to add about 10 new rows after pageload. It should check if there is an article with id (that is actually loading). If its not, add 10 of that id with different tag id.
$sprawdz = "SELECT id_artykulow FROM tag_art WHERE id_artykulow='".$_GET['id']."' " ;
$miasto = mysql_query($sprawdz);
$a = mysql_num_rows($miasto);
while ($a<=10){
$zm = "SELECT id FROM tag_content ORDER BY RAND() LIMIT 1";
$sw = mysql_query($zm);
while($row3=mysql_fetch_array($sw)){
$zmienna = "INSERT INTO tag_art(id_artykulow, id_tagow) VALUES ('".$_GET['id']."', '".$row3['id']."' ) ";
$cokolwiek = mysql_query($zmienna);
}
$a++;
}
There is two tables. One tag_content with id (of the tags), and another tag_art with id_artykulow (= id of the article) and id_tagow (id of the tag taken from tag_content)
Don't know why, but it doesn't add 10 rows (it should be for example ten id_artykulow = 10, with different id_tagow). How to fix it?
Thx for help and let me know if u need more informations (like more code etc.)
why do you have 2 while loops?
cant you just replace
while ($a<=10){
$zm = "SELECT id FROM tag_content ORDER BY RAND() LIMIT 1";
with
if ($a<=10){
$zm = "SELECT id FROM tag_content ORDER BY RAND() LIMIT " . (10-$a);
or just let the databse do all the work by:
$query = "INSERT INTO tag_art(id_artykulow, id_tagow) SELECT '".$_GET['id']."', id FROM tag_content ORDER BY RAND() LIMIT " . (10-$a);
(and i would also recomendate protection agains sql-injections, mysql_real_escape_string())
Or let the database do all the work:
// store id as mysql-variable, but let php force it to an integer first
mysql_query("SET #id = " . (int) $_GET['id']);
// calculate how many new art we need, to get 10, using greatest to avoid negative numbers
mysql_query("SELECT #art_needed := GREATEST(0, 10 - COUNT(*)) FROM tag_art WHERE id_artykulow = #id");
// Need to use prepere to be able to have an mysql-variable as limit
mysql_query("PREPARE art_stmt FROM 'INSERT INTO tag_art(id_artykulow, id_tagow) SELECT ?, id FROM tag_content ORDER BY RAND() LIMIT ?'");
// execute the query using the mysql-variables
mysql_query("EXECUTE art_stmt USING #id, #art_needed");
just reread my old answer, and no longer agrees with "or just let the databse do all the work by" for that answer, the database could do alot more.