When I delete rows in my database, the ID (auto_ increment) now longer to be in serial. Assuming I have 1 2 3 4 5 6 7 8 9 and I delete rows 3 4 5. After deletion I want ID to appear as 1 2 3 4 5 6 instead of 1 2 6 7 8 9
Please how can I do this ?
UPDATE
I am using this code to display serial numbers to the comments generated from the db...(inside a while loop)
<?php
$serial = 0;
$serial++;
echo"<div class='commentserial'>
<div id='$serial'></div>
<a href='#$serial'>$serial</a>
</diV>";
?>
Now that I have a pagination script on the comments display, when I click the second page instead of the serial numbering starts from 1 to $per_page Number.
So I felt if I use the database ID then the numbering wont start from 1 on subsequent paginated pages.
What you want to do would not be good practice. Holes in primary keys are supposed not to be left there. Imagine for example having a reference in another table to ID 25 in your main table. If something changes in the main table, the reference would suddenly point to a different record.
The same goes for, say, web links. Having a URL like
details.html?id=255
suddenly point to a different record would be very bad.
If you want a perfectly serial ID, you'll probably be best off creating it on application level.
use: SELECT * FROM table_name LIMIT offset, row_count
example:
if(isset($_GET['page'])) $page=$_GET['page'];
else $page=1;
$row_count=10;
$offset=($page-1)*$row_count;
$sql="select * from table1 limit $offset,$row_count";
autoincrement is intended to be used only on synthetic keys. Those keys do not have any semantic meaning and therefore it doesn't matter whether they are in sequence or not.
If your ID column has a semantic meaning, you should give it a meaningful name and do not use autoincrement on it (you can consider creating a new synthetic key with autoincrement, if you need it).
To implement pagination you can use the database query for it. Consider the mysql keywords LIMIT and OFFSET. This way your code generating the links does not have to concern about holes in your ID sequence.
Related
This is a problem with a ordering search results on my website,
When a search is made, random results appear on the content page, this page includes pagination too. I user following as my SQL query.
SELECT * FROM table ORDER BY RAND() LIMIT 0,10;
so my questions are
I need to make sure that everytime user visits the next page, results they already seen not to appear again (exclude them in the next query, in a memory efficient way but still order by rand() )
everytime the visitor goes to the 1st page there is a different sets of results, Is it possible to use pagination with this, or will the ordering always be random.
I can use seed in the MYSQL, however i am not sure how to use that practically ..
Use RAND(SEED). Quoting docs: "If a constant integer argument N is specified, it is used as the seed value." (http://dev.mysql.com/doc/refman/5.0/en/mathematical-functions.html#function_rand).
In the example above the result order is rand, but it is always the same. You can just change the seed to get a new order.
SELECT * FROM your_table ORDER BY RAND(351);
You can change the seed every time the user hits the first results page and store it in the user session.
Random ordering in MySQL is as sticky a problem as they come. In the past, I've usually chosen to go around the problem whenever possible. Typically, a user won't ever come back to a set of pages like this more than once or twice. So this gives you the opportunity to avoid all of the various disgusting implementations of random order in favor of a couple simple, but not quite 100% random solutions.
Solution 1
Pick from a number of existing columns that already indexed for being sorted on. This can include created on, modified timestamps, or any other column you may sort by. When a user first comes to the site, have these handy in an array, pick one at random, and then randomly pick ASC or DESC.
In your case, every time a user comes back to page 1, pick something new, store it in session. Every subsequent page, you can use that sort to generate a consistent set of paging.
Solution 2
You could have an additional column that stores a random number for sorting. It should be indexed, obviously. Periodically, run the following query;
UPDATE table SET rand_col = RAND();
This may not work for your specs, as you seem to require every user to see something different every time they hit page 1.
First you should stop using the ORDER BY RAND syntax. This will bad for performance in large set of rows.
You need to manually determine the LIMIT constraints. If you still want to use the random results and you don't want users to see the same results on next page the only way is to save all the result for this search session in database and manipulate this information when user navigate to next page.
The next thing in web design you should understand - using any random data blocks on your site is very, very, very bad for users visual perception.
You have several problems to deal with! I recommend that you go step by step.
First issue: results they already seen not to appear again
Every item returned, store it in one array. (assuming the index id on the example)
When the user goes to the next page, pass to the query the NOT IN:
MySQL Query
SELECT * FROM table WHERE id NOT IN (1, 14, 25, 645) ORDER BY RAND() LIMIT 0,10;
What this does is to match all id that are not 1, 14, 25 or 645.
As far as the performance issue goes: in a memory efficient way
SELECT RAND( )
FROM table
WHERE id NOT
IN ( 1, 14, 25, 645 )
LIMIT 0 , 10
Showing rows 0 - 9 (10 total, Query took 0.0004 sec)
AND
SELECT *
FROM table
WHERE id NOT
IN ( 1, 14, 25, 645 )
ORDER BY RAND( )
LIMIT 0 , 10
Showing rows 0 - 9 (10 total, Query took 0.0609 sec)
So, don't use ORDER BY RAND(), preferably use SELECT RAND().
I would have your PHP generate your random record numbers or rows to retrieve, pass those to your query, and save a cookie on the user's client indicating what records they've already seen.
There's no reason for that user specific data to live on the server (unless you're tracking it, but it's random anyway so who cares).
The combination of
random ordering
pagination
HTTP (stateless)
is as ugly as it comes: 1. and 2. together need some sort of "persistent randomness", while 3. makes this harder to achieve. On top of this 1. is not a job a RDBMS is optimized to do.
My suggestion depends on how big your dataset is:
Few rows (ca. <1K):
select all PK values in first query (first page)
shuffle these in PHP
store shuffled list in session
for each page call select the data according to the stored PKs
Many rows (10K+):
This assumes, you have an AUTO_INCREMENT unique key called ID with a manageable number of holes. Use a amintenace script if needed (high delete ratio)
Use a shuffling function that is parameterized with e.g. the session ID to create a function rand_id(continuous_id)
If you need e.g. the records 100,000 to 100,009 calculate $a=array(rand_id(100,000), rand_id(100,001), ... rand_id(100,009));
$a=implode(',',$a);
$sql="SELECT foo FROM bar WHERE ID IN($a) ORDER BY FIELD(ID,$a)";
To take care of the holes in your ID select a few records too many (and throw away the exess), looping on too few records selected.
I am new in forum, and need some help to do one functionality for my unity game. I am trying to save the progress of the player in one mysql database, like this:
userid level stars
29 1 2
29 2 1
45 1 3
50 1 2
50 2 3
50 3 1
29 3 3
so the script send the userid provided by the user registration in the begining of the game. and for each level he complete, the script send the number of the level, and the amount of stars collected in the level..
the problem and question is, how I configure this in the php script and mysql database to save the information only once? because if the player with the id 50 play the first level, will add a line with the information, but if the same player play the first level again and change the amount of stars, I dont want a new line, just update the stars amount.
I take a look in the INDEX, UNIQUE, PRIMARY, FULLTEXT, SPATIAL functions but dont figured out what is the correct combination and how to put in the php script, and take a look in other questions in the forum but nothing like this.
thanks for the help!
I recommend you use http://redis.io/ (in-memory data structure store, used as database, cache and message broker) to save progress in the games.
First you want an unique index on the combination (userid, level) and then you want to do an update if the combination exists and an insert otherwise.
For how to create the unique index please take a look at How do I specify unique constraint for multiple columns in MySQL?
For how to code the SQL query to do update/insert please take a look at SQL: If Exists Update Else Insert
The article above uses Microsoft SQL syntax. In PHP you can code this by issuing the query and then using mysql_affected_rows to see how many rows where affected. If 0 rows where affected then you issue the INSERT query from PHP.
in pseudo code you need to do something like this in SQL.
UPDATE $table set column=value WHERE id=$ID
Hi brayan actually the problems is that no one will write code for you, you have to do it yourself. I guess you are unaware with SQL i.e., you asked that
how I configure this in the php script and mysql database to save the
information only once? because if the player with the id 50 play the
first level, will add a line with the information, but if the same
player play the first level again and change the amount of stars, I
dont want a new line, just update the stars amount.
Anyhow You first required some basic understanding of SQL and PHP with Unity. I will recommend you this Guide Server_Side_Highscores of unityWiki it help you to make database and server logic intergartion with PHP.
Now for your Second important part of question.
You have to update user code after each level completion.Or you can simply ask to user about socre save.
Before inserting new record into the database you have to check that userId with level id alread exist or not. some thing like this
Select userid, level, stars
from youTableName
where userid = ?
and level = ?
if the above query return empty response then you simply need to add the record
INSERT INTO table_name (userid, level, stars)
VALUES (value1,value2,value3);
Otherwise you have to update that specific column.
I'm facing a problem to create a function for moving up / down records in MySQL database. My current table looks like:
Id UNSIGNED INT AI PRIMARY | Some other columns | Sort UNSIGNED INT INDEX
Let's say I've got some data:
1 | FirstRecord | 1
2 | Second | 2
3 | Third | 3
4 | 4th | 4
Much more data...
After action 'Move Up' on 'Id = 4' I want 'Id = 4' to get 'Sort' of 'Id #above' and 'Id #above' to get 'Sort' of 'Id = 4'
What I have on the begginig:
Id of record I want to move
The direction I want to move (up / down)
What I want to have in the end
My record moved up or down (swapped 'Sort' values)
Consecutive numbers in 'Sort' column
How I want to do it
Because I'm using php5.4 I can use some code in this language, not only pure sql
I must be prepared for high load and simultaneous requests
I don't want to create MySQL procedures or functions. The best way will be do do it in one simple query
What I've tried
The simplest way was to use php and:
Get 'Sort' of current Id (1st query)
Find Id of column above / below (2nd query)
Get 'Sort' of this column (3rd query)
Swap 'Sort' values (4th and 5th query)
Pros are that this method is quite simple, and i think thats all.
Cons are that for a moment both rows have the same 'Sort' value. Another is that when 2 scripts runs in the same time, the result may be unpredicted. Also after deleting any record, there would be a hole in numeration.
More complicated, also using php
Change 'Sort' to FLOAT (at the beggining, not every time)
Substract or Add 1.5 from the record.
Update or records in SQL query to make the numbers consecutive
Pros: no need to read antything about next / previous record. After each move we are sure, that 'Sort' numbers will be ok. We can use UNIQUE on Sort.
Cons: In huge tables it would take lots of CPU time to assign new Sort numbers. Am I right? We also have 'Sort' in different type than Id...
Similar to previous
Substract / Add 1 from / to record we want to move.
Assign consecutive numbers by query using our Id as second Sort parameter.
Pros: Same as above, but no way to use UNIQUE. But we have 'Sort' in same type as Id
Cons: For some time both records have the same 'Sort', high cpu usage (?)
Up to now these are the best methods I know about. Does anybody of you know any other, linking all pros and not having cons?
Thanks for your replays.
You'll need 1 query for the record you want to move to get the sort index. Then you should have the new sort index an input from the sort UI.
If you're just swapping two items you can do it in one query:
UPDATE table SET sort_index = IF(id === ?id?, ?new_sort_index?, ?old_sort_index?) WHERE id = ?id? OR sort_index = ?new_sort_index?
Using the IF you update two records at one.
If you can move one item many places you need to do a range update. First figure out the direction: up/down. Then do a query like:
UPDATE table SET sort_index = sort_index + 1 WHERE sort_index >= ?new_sort_index? AND sort_index < ?old_sort_index?
This created a space at ?new_sort_index? and removed a space at ?old_sort_index?
Then one final query to set the new sort index for the moved record.
The latter approach works if even if your index is sparse (ie. there are holes) the former doesn't, so keep that in mind.
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.
This is a problem with a ordering search results on my website,
When a search is made, random results appear on the content page, this page includes pagination too. I user following as my SQL query.
SELECT * FROM table ORDER BY RAND() LIMIT 0,10;
so my questions are
I need to make sure that everytime user visits the next page, results they already seen not to appear again (exclude them in the next query, in a memory efficient way but still order by rand() )
everytime the visitor goes to the 1st page there is a different sets of results, Is it possible to use pagination with this, or will the ordering always be random.
I can use seed in the MYSQL, however i am not sure how to use that practically ..
Use RAND(SEED). Quoting docs: "If a constant integer argument N is specified, it is used as the seed value." (http://dev.mysql.com/doc/refman/5.0/en/mathematical-functions.html#function_rand).
In the example above the result order is rand, but it is always the same. You can just change the seed to get a new order.
SELECT * FROM your_table ORDER BY RAND(351);
You can change the seed every time the user hits the first results page and store it in the user session.
Random ordering in MySQL is as sticky a problem as they come. In the past, I've usually chosen to go around the problem whenever possible. Typically, a user won't ever come back to a set of pages like this more than once or twice. So this gives you the opportunity to avoid all of the various disgusting implementations of random order in favor of a couple simple, but not quite 100% random solutions.
Solution 1
Pick from a number of existing columns that already indexed for being sorted on. This can include created on, modified timestamps, or any other column you may sort by. When a user first comes to the site, have these handy in an array, pick one at random, and then randomly pick ASC or DESC.
In your case, every time a user comes back to page 1, pick something new, store it in session. Every subsequent page, you can use that sort to generate a consistent set of paging.
Solution 2
You could have an additional column that stores a random number for sorting. It should be indexed, obviously. Periodically, run the following query;
UPDATE table SET rand_col = RAND();
This may not work for your specs, as you seem to require every user to see something different every time they hit page 1.
First you should stop using the ORDER BY RAND syntax. This will bad for performance in large set of rows.
You need to manually determine the LIMIT constraints. If you still want to use the random results and you don't want users to see the same results on next page the only way is to save all the result for this search session in database and manipulate this information when user navigate to next page.
The next thing in web design you should understand - using any random data blocks on your site is very, very, very bad for users visual perception.
You have several problems to deal with! I recommend that you go step by step.
First issue: results they already seen not to appear again
Every item returned, store it in one array. (assuming the index id on the example)
When the user goes to the next page, pass to the query the NOT IN:
MySQL Query
SELECT * FROM table WHERE id NOT IN (1, 14, 25, 645) ORDER BY RAND() LIMIT 0,10;
What this does is to match all id that are not 1, 14, 25 or 645.
As far as the performance issue goes: in a memory efficient way
SELECT RAND( )
FROM table
WHERE id NOT
IN ( 1, 14, 25, 645 )
LIMIT 0 , 10
Showing rows 0 - 9 (10 total, Query took 0.0004 sec)
AND
SELECT *
FROM table
WHERE id NOT
IN ( 1, 14, 25, 645 )
ORDER BY RAND( )
LIMIT 0 , 10
Showing rows 0 - 9 (10 total, Query took 0.0609 sec)
So, don't use ORDER BY RAND(), preferably use SELECT RAND().
I would have your PHP generate your random record numbers or rows to retrieve, pass those to your query, and save a cookie on the user's client indicating what records they've already seen.
There's no reason for that user specific data to live on the server (unless you're tracking it, but it's random anyway so who cares).
The combination of
random ordering
pagination
HTTP (stateless)
is as ugly as it comes: 1. and 2. together need some sort of "persistent randomness", while 3. makes this harder to achieve. On top of this 1. is not a job a RDBMS is optimized to do.
My suggestion depends on how big your dataset is:
Few rows (ca. <1K):
select all PK values in first query (first page)
shuffle these in PHP
store shuffled list in session
for each page call select the data according to the stored PKs
Many rows (10K+):
This assumes, you have an AUTO_INCREMENT unique key called ID with a manageable number of holes. Use a amintenace script if needed (high delete ratio)
Use a shuffling function that is parameterized with e.g. the session ID to create a function rand_id(continuous_id)
If you need e.g. the records 100,000 to 100,009 calculate $a=array(rand_id(100,000), rand_id(100,001), ... rand_id(100,009));
$a=implode(',',$a);
$sql="SELECT foo FROM bar WHERE ID IN($a) ORDER BY FIELD(ID,$a)";
To take care of the holes in your ID select a few records too many (and throw away the exess), looping on too few records selected.