I'm writing a code which looks up a MYSQL table, hits an API and then writes the result to a table.
Initially I was using:
$select = "SELECT Partner, Merchant, IP FROM " .$old_table. " WHERE ID >= " .$startRow;
mysqli_query($db, $select);
This worked well, but then I realized all the tables I have may not have sequential ID numbers, or even ID numbers at all.
Is there a way to start at a specific row without ID numbers?
Rows in SQL aren't necessarily in order. So without a sequential ID (or other identifier, like a date), there's no way to get all rows after a certain point.
So, no, you can't start at a specific row without a way to ID it, and IDing the rows that should come after it.
Related
I want to create a PHP page which selects a random record from MySQL database (a string, which will be used as a unique "token"). I want to select this random record only once and never again afterwards.
In order to do so, I add an extra field to the table (named 'numberfield', containing number 0), which is incremented at the moment the specific record has been selected. This way, only records with the value of 0 in the numberfield table field can be selected. As soon as the random record has been selected the numberfield field is incremented to 1 and can not be selected anymore. I'm thinking about using the following PHP code:
$result = mysql_query("SELECT token FROM table WHERE numberfield < **1** ORDER BY RAND() LIMIT 0,1");
if (!$result) {
echo 'Could not run query: ' . mysql_error();
exit;
}
$row = mysql_fetch_row($result);
echo $row[0];
mysql_query("UPDATE table SET numberfield=numberfield+1 WHERE token=" + $row[0] + "");
Will this be the right way to do it ? Any thoughts ?
Furthermore, I want to avoid a different random record is selected at page refresh. What will be the right and most simple way to keep the "token" in cache ? For example, is it possible to keep the "token" in a session which will not be overwritten during page refresh, or do I have to use other techniques like Ajax etc. Your help and comment is highly appreciated !
You should stop using mysql_ functions as they are deprecated.
You should avoid using ORDER BY RAND() in larger tables because of overhead incurred from seeking a random number.
To accomplish a SELECT ... UPDATE you would need some sort of locking. There is a slim chance that a row could be randomly selected twice. This can be prevented using a stored procedure.
You can just use the session id generated by PHP or a part of it. This topic talks about how unique a session id is and this topic discusses the varying lengths.
You can alternatively create a random string on the PHP side which would save overhead from connecting to the database.
I have a MySQL database that contains over 400,000 rows. For my web based script, I have a page function. One of the steps to determine how many pages there should be is returning the number of rows in the table.
Let's pretend the table name is data.
I'm wondering what is the most efficient method to ONLY return the number of rows in the database.
I could obviously do something like:
$getRows = mysql_query("SELECT id FROM `data`") or die(mysql_error());
$rows = mysql_num_rows($getRows);
So that it only selects the id. But still, that will be selecting 400,000 + ID's worth of data and storing it on the stack (i think?) and seems less efficient as using a method such as finding the table status. I'm just not 100% sure how to use the table status method.
Feedback & opinions would be awesome. Thanks guys!
use count
SELECT count(id) FROM data
See this question for more info on getting counts. Make sure your id has an index in your table.
Now, to find the number of unique rows, you can do
SELECT count(distinct(id)) FROM data
alternatively, if you want to find the highest ID number (if you ID are autoincremental and unique) you can try SELECT max(id) FROM data to return the highest ID number present.
I'd highly recommend this site to learn these basic functions:
http://sqlzoo.net/
400,000 rows is not a lot at all. Keep it simple and just do:
select count(*)
from `data`
How can i get all of the records in a table that are out of
sequence so I know which account numbers I can reuse. I have a range
of account numbers from 50100 to 70100. I need to know which account
numbers are not stored in the table (not currently used) so I can use.
For instance say I have the following data in table:
Account Name
------ --------
50100 Test1
50105 Test2
50106 Test4
..
..
..
I should see the results:
50101
50102
50103
50104
because 50101-50104 are available account numbers since not currently in
table.
copied from http://bytes.com/topic/sql-server/answers/78426-get-all-unused-numbers-range
With respect to MYSQL and PHP.
EDITED
My range is 10000000-99999999.
My present way is using MySql query:
'SELECT FLOOR(10000000 + RAND() * 89999999) AS random_number FROM contacts WHERE "random_number" NOT IN (SELECT uid FROM contacts) LIMIT 1';
Thanks.
solution 1:
Generate a table with all possible accountnumbers in it. Then run a query similar to this:
SELECT id FROM allIDs WHERE id NOT IN (SELECT id FROM accounts)
Solution 2:
Get the whole id colummn into an array in php or java orso. Then run a for-loop to check if the number is in the array.
$ids = (array with all ids form the table)
for($i=50100;$i<=70100;$i++){
if(array_search($i, $ids) != -1){
$availableids[] = $i;
}
}
one way would be to create another table - fill it will all allowable numbers, then write a simple query to find the ones in the new table that are not in the original table.
Sort the accounts in the server, and find jumps in PHP while reading in the results. Any jump in the sorted sequence is "free for use", because they are ordered. You can sort with something like SELECT AccountNumber FROM Accounts SORT ASCENDING;.
To improve efficiency, store the free account numbers in another table, and use numbers from this second table until no more remain. This avoids making too many full reads (as in the first paragraph), which may be expensive. While you are at it, you may want to add a hook in the part of the code which deletes accounts, so they are immediately included in this second table, making the first step unnecessary.
I have a web page where people are able to post a single number between 0 and 10.
There is like a lotto single number generation once daily. I want my PHP script to check on the the posted numbers of all the users and assign a score of +1 or -1 to the relative winners (or losers).
The problem is that once I query the DB for the list of the winning users, I want to update their "score" field (in "users" table). I was thinking of a loop like this (pseudocode)
foreach winner{
update score +1
}
but this would mean that if there are 100 winners, then there will be 100 queries. Is there a way to do some sort of batch inserting with one single query?
Thanks in advance.
I'll assume you are using a database, with sql, and suggest that would probably want to do something like
UPDATE `table` SET `score`=`score`+1 WHERE `number`=3;
and the corresponding -1 for losers (strange, can't see a reason to -1 them).
Without more details though, I can't be of further help.
You didn't specify how the numbers were stored. If there is a huge number of people posting, a good option is to use a database to store their numbers.
You can have for example a table called lotto with three fields: posted_number, score and email. Create an (non-unique!) index on the posted_number field.
create table lotto (posted_number integer(1) unsigned, score integer, email varchar(255), index(posted_number));
To update their score you can execute two queries:
update lotto set score = score+1 where posted_number = <randomly drawn number here>
update lotto set score = score-1 where posted_number = <randomly drawn number here>
Let's just assume we have a datatable named posts and users.
Obviously, users contain the data of the gambler (with a convenient id field and points for the number of points they have), and posts contain the post_id ID field for the row, user_id, which is the ID of the user and value, the posted number itself.
Now you only need to implement the following SQL queries into your script:
UPDATE users INNER JOIN posts ON users.id = posts.user_id SET users.points = (users.points + 1)
WHERE posts.value = 0;
Where 0 at the end is to be replaced with the randomly drawn number.
What will this query do? With the INNER JOIN construct, it will create a link between the two tables. Automatically, if posts.value matches our number, it will link posts.user_id to users.id, knowing which user has to get his/her points modified. If someone gambled 0, and his ID (posts.user_id) is 8170, the points field will update for the user having user.id = 8170.
If you alter the query to make it (users.points - 1) and WHERE posts.value != 0, you will get the non-winners having one point deducted. It can be tweaked as much as you want.
Just be careful! After each daily draw, the posts table needs to be truncated or archived.
Another option would be storing the timestamp (time() in PHP) of the user betting the number, and when executing, checking against the stored timestamp... whether it is in between the beginning and the end of the current day or not.
Just a tip: you can use graphical database software (like Microsoft Access or LibreOffice Base) to have your JOINs and such simulated on a graphical display. It makes modelling such questions a lot easier for beginners. If you don't want desktop-installed software, trying out an installation of phpMyAdmin is another solution too.
Edit:
Non-relational databases
If you are to use non-relational databases, you will first need to fetch all the winner IDs with:
SELECT user_id FROM posts WHERE value=0;
This will give you a result of multiple rows. Now, you will need to go through this result, one-by-one, and executing the following query:
UPDATE users SET points=(users.points + 1) WHERE id=1;
(0 is the drawn winning number, 1 is the concurrent id of the user to update.)
Without using the relation capabilities of MySQL, but using a MySQL database, the script would look like this:
<?php
$number = 0; // This is the winning number we have drawn
$result = mysql_query("SELECT user_id FROM posts WHERE number=" .$number);
while ( $row = mysql_fetch_assoc($result) )
{
$curpoints_result = mysql_query("SELECT points FROM users WHERE user_id=" .$row['user_id']);
$current_points = mysql_fetch_assoc($curpoints_results);
mysql_query("UPDATE users SET points=" .($current_points['points'] + 1). " WHERE user_id=" .$row['user_id']);
}
?>
The while construct make this loop to run until every row of the result (list of winners) is updated.
Oh and: I know MySQL is a relational database, but it is just what it is: an example.
Storing randomly picked rows in session?
Hi!
I’m building a PHP script that outputs a random word from a MySQL table. Each time the script is refreshed I want a new word to display. (It is connected to jquery – so the data output of the php-file is directly displayed on my page)
However, I want to display each word only once. If all the words are picked, I want the script to reset and start picking over again.
Right now I have done this by setting up an additional table called “visited” and putting all the picked rows from table “wordlist” in there, with the users unique session-id to
prevent results from multiple users to interfere with eachother.
So the query goes like this:
session_start();
$id = session_id();
$random_sql = "SELECT *
FROM wordlist AS a
LEFT JOIN visited AS b ON a.word = b.word
AND b.sessionid = '$id'
WHERE b.word IS NULL
ORDER BY a.weight * rand( ) DESC // Weighted random
LIMIT 1";
$random_row = mysql_query($random_sql);
if(mysql_num_rows($random_row) > 0)
{
while($row = mysql_fetch_row($random_row))
{
$insert_query = "INSERT INTO visited (ID, word, sessionid, date) VALUES ('$row[0]', '$row[1]', '$id', CURDATE())";
$insert = mysql_query($insert_query) or die (mysql_error());
echo $row[1];
}
This works perfectly fine, but I reckon it would be hard for the database to handle many visitors at the same time?
So my question is:
How can I store the information of “visited” words in a session and exclude them from the query?
One more thing: I’m estimating that the wordlist-table will have around 8000 rows. Will this be too many for the ORDER BY RAND-function, and render out to be noticeably slow?
Thanks!
This depends on how much the data must be persistent. If you don't need persistency then session is of course much more efficient in this case. You can store there any PHP data structure, i.e. I guess you'd use associative array in this case.
Regarding performance: if the words are indexed sequentially, you can think of generating the random number as a direct id and just retrieve the particular row directly. ORDER BY RAND() must generate all the numbers and sort them, which is much less efficient than just generate one id like RAND() * MAX(ID).
Read more here.