I have this MySQL query :
while ($x <= 9) {
$data_1 = "SELECT scene FROM star WHERE star LIKE '%".$star."%' ORDER BY RAND() LIMIT 1";
$result_1 = mysql_query ($data_1) OR die("Error: $data_1 </br>".mysql_error());
while($row_1 = mysql_fetch_object($result_1)) {
$scene = $row_1->scene;
$x = $x + 1;
}
}
I want to get everytime a new scene for each execution, but I always get the same scene. Whats the issue? Can someone make me a few pointers in which direction I have to search ?
What you need to do is tie a random seed to each row, and tie a new one each time. Do this by assigning a random value as an aliased transient column to your table, and then select from it.
SELECT s.scene as scene FROM (
SELECT stars.scene as scene, RAND() as seed
FROM stars
WHERE star LIKE '%".$star."%'
ORDER BY seed
) s
LIMIT 1;
Using PDO it's going to look something like this:
function getScene() {
$sql = 'SELECT s.scene as scene FROM ( SELECT stars.scene as scene, RAND() as seed FROM stars WHERE star LIKE '%:star%' ORDER BY seed ) s LIMIT 1;';
$query = $this->db->prepare($sql);//'db' is the PDO connection
$query->execute(array(':star' => "Allison Brie"));
foreach ($conn->query($sql) as $row) {
print $row['scene'] . "\t";
}
}
I'm not sure what you were trying to accomplish with the rest of your code, but it mostly looks like cruft.
Related
I have a table called feedbacks that looks like this:
id user type
1 JOhnT Positive
2 JOhnT Negative
3 Sarah Positive
4 JOhnT Positive
5 JOhnT Neutral
....................
I need to get the percentage of POSITIVE feedback for each user using PHP.
I tried something like this which i know it is wrong:
$sql = "SELECT type, count(*),
concat(round(( count(*)/(SELECT count(*) FROM feedbacks WHERE user='JOhnT' AND type='POSITIVE') * 100 ),2),'%') AS percentage
FROM feedback
WHERE user='$email' AND type='positive' GROUP BY type";
$query = mysqli_query($db_conx, $sqlJ);
echo $sql;
Could someone please advice on how to achieve this?
EDIT:
Based on the comments, this is what i have so far:
$sql = "SELECT * FROM feedbacks WHERE user='JOhnT' AND type='POSITIVE'";
$query = mysqli_query($db_conx, $sql) or die(mysqli_error($db_conx));
$productCount = mysqli_num_rows($query);
if ($productCount > 0) {
while($row = mysqli_fetch_array($query, MYSQLI_ASSOC)){
///do I need to calculate the percentage here?//
//if so, how?////
}
}
I ended up creating an array and push each $row in my whole loop into the array and then calculate the percentage like this:
$c = count($values);
$array = $values;
function array_avg($array, $round=1){
$num = count($array);
return array_map(
function($val) use ($num,$round){
return array('count'=>$val,'avg'=>round($val/$num*100, $round));
},
array_count_values($array));
}
$rating = 0;
if($c > 0){
$avgs = array_avg($array);
$rating = $avgs["positive"]["avg"];
}
This works fine for now.
You can do this a conditional average. In MySQL, you could phrase this as:
select user, avg(type = 'Positive') positive_ratio
from feedback
group by user
This gives you, for each user, a value between 0 and 1 that represents the ratio of positive types. You can multiply that by 100 if you want a percentage.
If you want this information for a single user, you can filter with a where clause (and there is no need to group by):
select user, avg(type = 'Positive') positive_ratio
from feedback
where user = 'JOhnT'
Side note: user is a MySQL keyword, hence not a good choice for a column name.
I'm trying to create a pagination for my PDO query. I cant figure it out. I've tried numerous google searches, but nothing that will work for me. [I probably didn't search hard enough. I'm not sure]
This is my code:
$sql2 = "SELECT * FROM comments WHERE shown = '1'ORDER BY ID DESC";
$stm2 = $dbh->prepare($sql2);
$stm2->execute();
$nodes2= $stm2->fetchAll();
foreach ($nodes2 as $n1) {
echo "text";
}
I want to be able to limit 10 comments per page, and use $_GET['PAGE'] for the page.
Something that I tried
$sql2 = "SELECT * FROM comments WHERE shown = '1'ORDER BY ID DESC";
$stm2 = $dbh->prepare($sql2);
$stm2->execute();
$nodes2= $stm2->fetchAll();
$page_of_pagination = 1;
$chunked = array_chunk($nodes2->get_items(), 10);
foreach ($chunked[$page_of_pagination] as $n1) {
echo "text";
}
If someone could help out, I appreciate it.
You need to limit the query that you are performing, getting all values from the database and then limiting the result to what you want is a bad design choice because it's highly inefficient.
You need to do this:
$page = (int)$_GET['PAGE']; // to prevent injection attacks or other issues
$rowsPerPage = 10;
$startLimit = ($page - 1) * $rowsPerPage; // -1 because you need to start from 0
$sql2 = "SELECT * FROM comments WHERE shown = '1' ORDER BY ID DESC LIMIT {$startLimit}, {$rowsPerPage}";
What LIMIT does:
The LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT takes one or two numeric arguments, which must both be nonnegative integer constants
More information here: http://dev.mysql.com/doc/refman/5.7/en/select.html
Then you can proceed getting the result and showing it.
Edit after comment:
To get all the pages for display you need to know how many pages are there so you need to do a count on that SELECT statement using the same filters, meaning:
SELECT COUNT(*) as count FROM comments WHERE shown = '1'
Store this count in a variable. To get the number of pages you divide the count by the number of rows per page you want to display and round up:
$totalNumberOfPages = ceil($count / $rowsPerPage);
and to display them:
foreach(range(1, $totalNumberOfPages) as $pageNumber) {
echo '' . $pageNumber . '';
}
I'm trying to do 2 things.
1) Get the amount of rows in this query
SELECT
COUNT(*)
FROM
`my_table`
WHERE
`column_1` = 152
AND
`column_2` = 42
ORDER BY
`column_3`
As you can see that is no problem ^^
2) Determine the number within the range of rows that is returned by id
Ex: ID 765 is Item 4 of 7 where column_1 = 152 and column_3 = 42
Does anyone have any basic solutions to this problem with almost pure MySQL? I'd like to avoid iterating through all the rows and setup a counter to increment until it matches current id like this:
$sql = '
SELECT
*
FROM
`my_table`
WHERE
`column_1` = 152
AND
`column_2` = 42
ORDER BY
`column_3`
';
$query = mysqli_query($sql);
$current_id = 2523;
$i = 1;
while ($row = mysqli_fetch_assoc($query)) {
if ($row['id'] == $current_id) {
$current_position = $i;
}
$i++;
}
print 'Current position in range is: '. $current_position;
Also please don't worry about the actual syntax, I won't be using this exact script, but you get the logic that I'd like to avoid using. If anyone has a better solution, please let me know. Thanks in advance!!
i have this code:
while ($sum<16 || $sum>18){
$totala = 0;
$totalb = 0;
$totalc = 0;
$ranka = mysql_query("SELECT duration FROM table WHERE rank=1 ORDER BY rand() LIMIT 1");
$rankb = mysql_query("SELECT duration FROM table WHERE rank=2 ORDER BY rand() LIMIT 1");
$rankc = mysql_query("SELECT duration FROM table WHERE rank=3 ORDER BY rand() LIMIT 1");
while ($rowa = mysql_fetch_array($ranka)) {
echo $rowa['duration'] . "<br/>";
$totala = $totala + $rowa['duration'];
}
while ($rowb = mysql_fetch_array($rankb)) {
$totalb = $totalb + $rowb['duration'];
}
while ($rowc = mysql_fetch_array($rankc)) {
$totalc = $totalc + $rowc['duration'];
}
$sum=$totala+$totalb+$totalc;
}
echo $sum;
It works fine, But the problem is until "$sum=16" the "echo $rowa['duration']" executes, the question is, is there a away to "echo" only the latest executed code in the "while ($rowa = mysql_fetch_array($ranka))" i this while loop?
Because most of the times returns all the numbers until the "$sum=16"
You are explicitly echoing the $rowa['duration'] in the first inner while loop. If you only want to print the last duration from the $ranka set, simple change the echo to $rowa_duration = $rowa['duration'] then echo it outside the loop.
while ($rowa = mysql_fetch_array($ranka)) {
$rowa_duration = $rowa['duration'];
$totala = $totala + $rowa['duration'];
}
echo $rowa_duration . '<br/>';
What you are doing there is bad on multiple levels. And your english horrid. Well .. practice makes perfect. You could try joining ##php chat room on FreeNode server. That would improve both your english and php skills .. it sure helped me a lot. Anyway ..
The SQL
First of all, to use ORDER BY RAND() is extremely ignorant (at best). As your tables begin the get larger, this operation will make your queries slower. It has n * log2(n) complexity, which means that selecting querying table with 1000 entries will take ~3000 times longer then querying table with 10 entries.
To learn more about it , you should read this blog post, but as for your current queries , the solution would look like:
SELECT duration
FROM table
JOIN (SELECT CEIL(RAND()*(SELECT MAX(id) FROM table)) AS id) as choice
WHERE
table.id >= choice.id
rank = 1
LIMIT 1
This would select random duration from the table.
But since you you are actually selecting data with 3 different ranks ( 1, 2 and 3 ), it would make sense to create a UNION of three queries :
SELECT duration
FROM table
JOIN (SELECT CEIL(RAND()*(SELECT MAX(id) FROM table)) AS id) as choice
WHERE
table.id >= choice.id
rank = 1
LIMIT 1
UNION ALL
SELECT duration
FROM table
JOIN (SELECT CEIL(RAND()*(SELECT MAX(id) FROM table)) AS id) as choice
WHERE
table.id >= choice.id
rank = 2
LIMIT 1
UNION ALL
SELECT duration
FROM table
JOIN (SELECT CEIL(RAND()*(SELECT MAX(id) FROM table)) AS id) as choice
WHERE
table.id >= choice.id
rank = 3
LIMIT 1
Look scary, but it actually will be faster then what you are currently using, and the result will be three entries from duration column.
PHP with SQL
You are still using the old mysql_* functions to access database. This form of API is more then 10 years old and should not be used, when writing new code. The old functions are not maintained (fixed and/or improved ) anymore and even community has begun the process of deprecating said functions.
Instead you should be using either PDO or MySQLi. Which one to use depends on your personal preferences and what is actually available to you. I prefer PDO (because of named parameters and support for other RDBMS), but that's somewhat subjective choice.
Other issue with you php/mysql code is that you seem to pointlessly loop thought items. Your queries have LIMIT 1, which means that there will be only one row. No point in making a loop.
There is potential for endless loop if maximum value for duration is 1. At the start of loop you will have $sum === 15 which fits the first while condition. And at the end that loop you can have $sum === 18 , which satisfies the second loop condition ... and then it is off to the infinity and your SQL server chokes.
And if you are using fractions for duration, then the total value of 3 new results needs to be even smaller. Just over 2. Start with 15.99 , ends with 18.01 (that's additional 2.02 in duration or less the 0.7 per each). Again .. endless loop.
Suggestion
Here is how i would do it:
$pdo = new PDO('mysql:dbname=my_db;host=localhost', 'username', 'password');
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$sum = 0;
while ( $sum < 16 )
{
$query = 'that LARGE query above';
$statement = $pdo->prepare( $query );
if ( $statement->execute() )
{
$data = $statement->fetchAll( PDO::FETCH_ASSOC );
$sum += $data[0]['duration']+$data[1]['duration']+$data[2]['duration'];
}
}
echo $data[0]['duration'];
This should do what your code did .. or at least, what i assume, was your intentions.
I want to show a random record from the database. I would like to be able to show X number of random records if I choose. Therefore I need to select the top X records from a randomly selected list of IDs
(There will never be more than 500 records involved to choose from, unless the earth dramatically increases in size. Currently there are 66 possibles.)
This function works, but how can I make it better?
/***************************************************/
/* RandomSite */
//****************/
// Returns an array of random site IDs or NULL
/***************************************************/
function RandomSite($intNumberofSites = 1) {
$arrOutput = NULL;
//open the database
GetDatabaseConnection('dev');
//inefficient
//$strSQL = "SELECT id FROM site_info WHERE major <> 0 ORDER BY RAND() LIMIT ".$intNumberofSites.";";
//Not wonderfully random
//$strSQL = "SELECT id FROM site_info WHERE major <> 0 AND id >= (SELECT FLOOR( COUNT(*) * RAND()) FROM site_info ) ORDER BY id LIMIT ".$intNumberofSites.";";
//Manual selection from available pool of candidates ?? Can I do this better ??
$strSQL = "SELECT id FROM site_info WHERE major <> 0;";
if (is_numeric($intNumberofSites))
{
//excute my query
$result = #mysql_query($strSQL);
$i=-1;
//create an array I can work with ?? Can I do this better ??
while ($row = mysql_fetch_array($result, MYSQL_NUM))
{
$arrResult[$i++] = $row[0];
}
//mix them up
shuffle($arrResult);
//take the first X number of results ?? Can I do this better ??
for ($i=0;$i<$intNumberofSites;$i++)
{
$arrOutput[$i] = $arrResult[$i];
}
}
return $arrOutput;
}
UPDATE QUESTION:
I know about the ORDER BY RAND(), I just don't want to use it because there are rumors it isn't the best at scaling and performance. I am being overly critical of my code. What I have works, ORDER BY RAND() works, but can I make it better?
MORE UPDATE
There are holes in the IDs. There is not a ton of churn, but any churn that happens needs to be approved by our team, and therefore could handled to dump any caching.
Thanks for the replies!
Why not use the Rand Function in an orderby in your database query? Then you don't have to get into randomizing etc in code...
Something like (I don't know if this is legal)
Select *
from site_info
Order by Rand()
LIMIT N
where N is the number of records you want...
EDIT
Have you profiled your code vs. the query solution? I think you're just pre-optimizing here.
If you dont want to select with order by rand().
Instead of shuffeling, use array_rand on the result:
$randKeys = array_rand($arrResult, $intNumberofSites);
$arrOutput = array_intersect_key(array_flip($randKeys), $arrResult);
edit: return array of keys not new array with key => value
Well, I don't think that ORDER BY RAND() would be that slow in a table with only 66 rows, but you can look into a few different solutions anyway.
Is the data really sparse and/or updated often (so there are big gaps in the ids)?
Assuming it's not very sparse, you could select the max id from the table, use PHP's built-in random function to pick N distinct numbers between 1 and the max id, and then attempt to fetch the rows with those ids from the table. If you get back less rows than you picked numbers, get more random numbers and try again, until you have the number of rows needed. This may not be particularly fast either.
If the data is sparse, I would set up a secondary "id-type" column that you make sure is sequential. So if there are 66 rows in the table, ensure that the new column contains the values 1-66. Whenever rows are added to or removed from the table, you will have to do some work to adjust the values in this column. Then use the same technique as above, picking random IDs in PHP, but you don't have to worry about the "missing ID? retry" case.
Here are the three functions I wrote and tested
My answer
/***************************************************/
/* RandomSite1 */
//****************/
// Returns an array of random rec site IDs or NULL
/***************************************************/
function RandomSite1($intNumberofSites = 1) {
$arrOutput = NULL;
GetDatabaseConnection('dev');
$strSQL = "SELECT id FROM site_info WHERE major <> 0;";
if (is_numeric($intNumberofSites))
{
$result = #mysql_query($strSQL);
$i=-1;
while ($row = mysql_fetch_array($result, MYSQL_NUM)) {
$arrResult[$i++] = $row[0]; }
//mix them up
shuffle($arrResult);
for ($i=0;$i<$intNumberofSites;$i++) {
$arrOutput[$i] = $arrResult[$i]; }
}
return $arrOutput;
}
JPunyon and many others
/***************************************************/
/* RandomSite2 */
//****************/
// Returns an array of random rec site IDs or NULL
/***************************************************/
function RandomSite2($intNumberofSites = 1) {
$arrOutput = NULL;
GetDatabaseConnection('dev');
$strSQL = "SELECT id FROM site_info WHERE major<>0 ORDER BY RAND() LIMIT ".$intNumberofSites.";";
if (is_numeric($intNumberofSites))
{
$result = #mysql_query($strSQL);
$i=0;
while ($row = mysql_fetch_array($result, MYSQL_NUM)) {
$arrOutput[$i++] = $row[0]; }
}
return $arrOutput;
}
OIS with a creative solution meeting the intend of my question.
/***************************************************/
/* RandomSite3 */
//****************/
// Returns an array of random rec site IDs or NULL
/***************************************************/
function RandomSite3($intNumberofSites = 1) {
$arrOutput = NULL;
GetDatabaseConnection('dev');
$strSQL = "SELECT id FROM site_info WHERE major<>0;";
if (is_numeric($intNumberofSites))
{
$result = #mysql_query($strSQL);
$i=-1;
while ($row = mysql_fetch_array($result, MYSQL_NUM)) {
$arrResult[$i++] = $row[0]; }
$randKeys = array_rand($arrResult, $intNumberofSites);
$arrOutput = array_intersect_key($randKeys, $arrResult);
}
return $arrOutput;
}
I did a simple loop of 10,000 iterations where I pulled 2 random sites. I closed and opened a new browser for each function, and cleared the cached between run. I ran the test 3 times to get a simple average.
NOTE - The third solution failed at pulling less than 2 sites as the array_rand function has different output if it returns a set or single result. I got lazy and didn't fully implement the conditional to handle that case.
1 averaged: 12.38003755 seconds
2 averaged: 12.47702177 seconds
3 averaged: 12.7124153 seconds
mysql_query("SELECT id FROM site_info WHERE major <> 0 ORDER BY RAND() LIMIT $intNumberofSites")
EDIT
Damn, JPunyon was a bit quicker :)
Try this:
SELECT
#nv := #min + (RAND() * (#max - #min)) / #lc,
(
SELECT
id
FROM site_info
FORCE INDEX (primary)
WHERE id > #nv
ORDER BY
id
LIMIT 1
),
#max,
#min := #nv,
#lc := #lc - 1
FROM
(
SELECT #min := MIN(id)
FROM site_info
) rmin,
(
SELECT #max := MAX(id)
FROM site_info
) rmax,
(
SELECT #lc := 5
) l,
site_info
LIMIT 5
This will select a random ID on each iteration using index, in descending order.
There is slight chance, though, that you get less results that you wanted, as it gives no second chance to the missed id's.
The more percent of rows you select, the bigger is the chance.
I would simply use the rand() function (I assume you are using MySQL)...
SELECT id, rand() as rand_idx FROM site_info WHERE major <> 0 ORDER BY rand_idx LIMIT x;
I'm with JPunyon. Use ORDER BY RAND() LIMIT $N. I think you'll get a bigger performance hit from $arrResult having and shuffling so many (unused) entries than from using the MySQL RAND() function.
function getSites ( $numSites = 5 ) {
// Sanitize $numSites if necessary
$result = mysql_query("SELECT id FROM site_info WHERE major <> 0 "
."ORDER BY RAND() LIMIT $numSites");
$arrResult = array();
while ( $row = mysql_fetch_array($result,MYSQL_NUM) ) {
$arrResult[] = $row;
}
return $arrResult;
}