Hallo i try to make a simple quiz application in php based on math tests from many years. I have database with such columns:
-id
-pytanie
-a
-b
-c
-d
-poprawna
-rok_id
-typ_id
I use rand function to get random id and next i use this in sql answer to get random question.
However id dont know how get radnom question for example random one question include yera_id=1
Firstly i use $numer=rand(1,1800)
My sql select is such as\
select pytanie, a,b,c,d, nazwa, rok_liczba, nazwa_typu, poprawna from pytania left join rok on rok.id= pytania.rok_id left join typ on typ.id=pytania.typ_id where typ_id=1 and pytania.id=".$numer.""
When i add to sql select ,,where year_id=1" i must click many time to hit when rand get 1 beacuse otherwise i dont get any resoult. It possible to rand from records ho are resoult a sql answer ?
You are computing a random number outside of the database then using it as a filter: but there is no guarantee that you have a record that matches your random value and the other filter on the question type.
I would recommend doing the random sort in the query itself. This should be as simple as adding this at the end of your query:
select ...
from ...
where typ_id = 1
order by rand() limit 1
Note that the exact syntax may vary across databases - the above is MySQL syntax.
Related
Introduction
I have a project where we help the IT community to organize better IT meetups (just like meetup.com but only for IT community) called https://codotto.com/
We are developing a new feature where we would like to show the number of usages of certain tags. The algorithm should work just like Stackoverflow's one. You write javascript and you get a list with the tags that match your query sorted by the most used ones.
I'm currently using Laravel but I will post the raw query so that it's easier for mysql wizards to help me out if possible :)
Problem
I have the following tables
tags table
id name
1 javascript
2 javascript-tools
3 javascript-security
group_has_tags table
group_id tag_id
1 2
2 2
2 3
We have the tags javascript-tools being used two times, javascript-security is used one while javascript is not used at all.
Now, if a user search for javascript, he should get first javascript (because it is a direct match) followed by the rest of the tags sorted by their usage.
In Laravel this is the code that I have (simplified ofc)
$tags = Tag::withCount('groups')
->orderBy('groups_count', 'DESC')
->where('name', 'LIKE', 'javascript%')
->get(2);
The problem is that since I only return back 2 results, javascript is not being included in the results, even tho it's what the user literally wrote
For the mysql magicians, here is the raw query
select
`tags`.*,
(
select
count(*)
from
`meetups`
inner join `meetup_has_tags` on `meetups`.`id` = `meetup_has_tags`.`meetup_id`
where
`tags`.`id` = `meetup_has_tags`.`tag_id`
) as `meetups_count`
from
`tags`
where
`title` LIKE 'javascript%'
order by
`meetups_count` desc
limit
2 offset 0
Question
The main objective here is to return the most relevant result to the user. He writes javascript and javascript shows up first followed by less "relevant" results. The way I found was to sort by the number of times a tag was used.
Is there a solution where I can do "please, fetch the results that match this query first, then return the most relevant results"?
By "most relevant" results, I simply mean "what the user is looking for". If he writes "javascript" it should return "javascript" followed by "javascript-tools" (because "javascript-tools" was used twice but the user is literally searching for "javascript")
Here is your query:
SELECT * FROM
(SELECT tags.*,COALESCE((SELECT COUNT(*) FROM group_has_tags WHERE tag_id = tags.id),0) AS usage
FROM tags
WHERE title LIKE 'javascript%') AS tmp
ORDER BY tmp.name = 'javascript' DESC,usage DESC
For each matching tag you get the number of times it has been used.
Then you first sort by whether the tag matches literally what the user has typed, then by the usage.
Of course you will have to parameterize this query but I hope you get the idea.
By running the following SQL command:
SELECT inl_cbsubs_subscriptions.user_id, inl_cbsubs_payment_items.subscription_id,
inl_cbsubs_payment_items.stop_date
FROM inl_cbsubs_subscriptions INNER JOIN
inl_cbsubs_payment_items ON inl_cbsubs_subscriptions.id=inl_cbsubs_payment_items.subscription_id
WHERE inl_cbsubs_subscriptions.user_id=596;
I get the following output:
As you can see, there are a variety of id values that are not always incremental. I need a way to modify the SQL statement so that the search will filter through the results and only provide a single output from the item which has the greatest id value. So, to show what I would like to see from the above example, here is a screenshot:
I am running the SQL statement in a PHP script, so if I need to implement any dynamic variables that would be available. Thanks you for your time.
You can use a DESC sorting on id and limit result with LIMIT 1.
I'm currently learning how to build a site in PHP MySQL. However, I seem to fail to understand COUNT() as count and wouldn't mind some further explanation.
I get the principles of COUNT, 0 || 1, and how it returns all the values that pertain to that query.
But, don't see how COUNT as count works. Anyhow, this is how the code I'm writing goes - so we have a working example - and where I first became perplexed.
"SELECT COUNT(id) as count, id
FROM user
WHERE email='$email' AND password='".md5$password."'"
That is what is called alias which is sometimes used to show a more appealing column header to users or the calling code
SELECT COUNT(`id`) as `count`....
will print
count
--------
5
The alias standing as the column header instead of any arbitrary string: See the SQLFiddle to see the difference
From the fiddle you can see that the header column looks somehow e.g.
count(*)
--------
5
With Count() you can count the returning rows of a result set. The also the official MySQL documentation about count:
Databases are often used to answer the question, “How often does a certain type of data occur in a table?” For example, you might want to know how many pets you have, or how many pets each owner has, or you might want to perform various kinds of census operations on your animals.
Counting the total number of animals you have is the same question as “How many rows are in the pet table?” because there is one record per pet. COUNT(*) counts the number of rows, so the query to count your animals looks like this:
SELECT COUNT(*) FROM pet;
The part with AS count means that this colum will get a name which you can use e.g. in PHP. See also this explenation on w3schools:
You can give a table or a column another name by using an alias. This can be a good thing to do if you have very long or complex table names or column names.
An alias name could be anything, but usually it is short.
as count is just an alias. You can use as for any field or method selected. it means you change the name of the column being returned in your dataset.
SELECT `field` as another_name
So:
SELECT COUNT(*) as `count`
Just renames the column from COUNT(*) to count making it easier to work with whereever you are maniuplating your result set.
It also makes for easier access within your current query. Many would do the following with large table names:
SELECT * FROM `table_with_ridiculous_name` as twrn WHERE twrn.id = 1
If you ran this sql:
SELECT COUNT(id), id ....
You would get (after doing a *_fetch_assoc) $row['numberofrecordshere'] which would be very hard to echo (or use in a comparison) unless you knew how many records there would be (which would defeat the purpose of this result, anyway)
Returning it as count allows you to get to it in the resulting array by using $row['count']
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.
Please note I am a beginner to this.
I have two questions:
1) How can I order the results of a query randomly.
example query:
$get_questions = mysql_query("SELECT * FROM item_bank_tb WHERE item_type=1 OR item_type=3 OR item_type=4");
2) The best method to select random rows from a table. So lets say I want to grab 10 rows at random from a table.
Many thanks,
If you don't mind sacrificing complexity on the insert/update/delete operations for speed on the select, you can always add a sequence number and make sure it's maintained on insert/update/delete, then whenever you do a select, simply select on one or more random numbers from within this range. If the "sequence" column is indexed, I think that's about as fast as you'll get.
An alternative is "shuffling". Add a sequence column, insert random values into this column, and whenever you select records, order by the sequence column and update the selected record sequences to new random values. The update should only affect the records you've retrieved, so shouldn't be too costly ... but it may be worth running some tests against your dataset.
This may be a fairly evil thing to say, but I'll say it anyway ... is there ever a need to display 'random' data? if you're trying to display random records, you may be doing something wrong.
Think about Amazon ... do they display random products, or do they display popular ones, and 'things other people bought when they looked at this'. Does SO give you a list of random questions to the right of here, or a list of related ones? Just some food for thought.
SELECT * FROM item_bank_tb WHERE item_type in(1,3,4) order by rand() limit 10
Beware that order by rand() is very slow on large recordset.
EDIT. Take a look at this very interesting article that presents a different approach.
http://explainextended.com/2009/03/01/selecting-random-rows/