I'm wondering what is command for database query that is querying data forward or back between rows? Just like forward and back button. Can someone give me an example? Thanks.
For examp:
$sql_xxxx = mysql_query("SELECT * FROM xxxx WHERE id='$xxx'") or die (mysql_error());
$row_xxxx = mysql_fetch_array($sql_xxxx);
Now I need the two same query but for one forward and in the other backward the data.
Since you tagged PHP and MySQL I think I can guess what you are trying to do;
Usually you can control this with the ID of a record in MySQL, for example:
SELECT * FROM MYTABLE WHERE ID = 1;
In PHP, you can construct dynamic queries to get different results while just changing the value of a variable.
Lets say we now want to take the same query and make it dynamic:
$id = 1;
$query = "SELECT * FROM MYTABLE WHERE ID = $id ";
as long as you execute this query, it will give you the row with ID = 1 , cause now it is taking the value from the $id variable.
If you want the next row, then you execute the same query but now $id must have the next value.
$id = 2;
Having a "NEXT" and "BACK" button can be matter of just adding or substracting 1 to the $id variable.
Still, this is only an example. In most of the cases you should not play with id's like that cause you should not assume that all id's exist, remember that "DELETE" exist;
So you can try to execute better a little query to find the next value like this:
to go foward:
$query= "SELECT MIN(ID) FROM MYTABLE WHERE ID > $id"
// This will get you for sure the closest id next to the current one
and to go back:
$query= "SELECT MAX(ID) FROM MYTABLE WHERE ID < $id"
I hope this helps,
Regards
You can specify a LIMIT in your query, which results in a specific number of rows. For instance, when you end your query with LIMIT 100, 10, you will get 10 results starting at row 100.
This way, you can build prev/next buttons, that when clicked, retrieve the previous or next page of results.
But in most other cases, you will just query everything you need and run through the result set. You do this by querying the result, and fetching each next row of the result.
If you use the LIMIT keyword, the database will happily return a "page" of data, for example;
SELECT * FROM posts ORDER BY post_time LIMIT 40,20; -- will return rows 41-60.
You can make use of that from PHP by just setting the first LIMIT number to page number * page size and the second number to page size (with page number being 0 for the first page). In the example, the page size would be 20 and the page number would be 2 (the third page) and the results will be all the posts from the third page.
There's nothing more to it from the database side, you'll just have to make good use of it from PHP.
if i'm understanding the question correctly, it sounds like you're trying to implement pagination in your queries and you would utilize the 'limit' clause, like so:
SELECT * FROM `your_table` LIMIT 5, 5
This will show records 6, 7, 8, 9, and 10
here's more documentation
Related
How to limit mysql rows to select newest 50 rows and have a next button such that next 50 rows are selected without knowing the exact number of rows?
I mean there may be an increment in number of rows in table. Well I will explain it clearly: I was developing a web app as my project on document management system using php mysql html. Everything is done set but while retrieving the documents I mean there may be thousands of documents.
All the documents whatever in my info table are retrieving at a time in home page which was not looking good. So I would like to add pages on such that only newest 50 documents are placed in first page next 50 are in second and so on.
But how come I know the exact number of rows every time and I cannot change the code every time a new document added so... numrows may not be useful I think...
Help me out please...
What you are looking for is called pagination, and the easiest way to implement a simple pagination is using LIMIT x , y in your SQL queries.
You don't really need the total ammount of rows you have, you just need two numbers:
The ammount of elemments you have already queried, so you know where you have to continue the next query.
The ammount of elements you want to list each query (for example 50, as you suggested).
Let's say you want to query the first 50 elements, you should insert at the end of your query LIMIT 0,50, after that you'll need to store somewhere the fact that you have already queried 50 elements, so the next time you change the limit to LIMIT 50,50 (starting from element number 50 and query the 50 following elements).
The order depends on the fields you are making when the entries are inserted. Normally you can update your table and add the field created TIMESTAMP DEFAULT CURRENT_TIMESTAMP and then just use ORDER BY created, because from now on your entries will store the exact time they were created in order to look for the most recent ones (If you have an AUTO_INCREMENT id you can look for the greater values aswell).
This could be an example of this system using php and MySQL:
$page = 1;
if(!empty($_GET['page'])) {
$page = filter_input(INPUT_GET, 'page', FILTER_VALIDATE_INT);
if(false === $page) {
$page = 1;
}
}
// set the number of items to display per page
$items_per_page = 50;
// build query
$offset = ($page - 1) * $items_per_page;
$sql = "SELECT * FROM your_table LIMIT " . $offset . "," . $items_per_page;
I found this post really useful when I first try to make this pagination system, so I recommend you to check it out (is the source of the example aswell).
Hope this helped you and sorry I coudn't provide you a better example since I don't have your code.
Search for pagination using php & mysql. That may become handy with your problem.
To limit a mysql query to fetch 50 rows use LIMIT keyword. You may need to find & store the last row id(50th row) so that you can continue with 51th to 100th rows in the next page.
Post what you have done with your code. Please refer to whathaveyoutried[dot]com
check this example from another post https://stackoverflow.com/a/2616715/6257039, you could make and orber by id, or creation_date desc in your query
I have a table that have hundreds of rows, and i want to get specific rows, I used the LIMIT and between id and id
In my application i have two text inputs, one is for START NUMBER and one is for END NUMBER, When i use the LIMIT i need to tell the user to make the right calculation to get the right start and end
So for example if i have a table of 3000 rows, and i want to select 100 rows above 2000 the query will be :
Select * from table LIMIT 2000,100
This will select 100 rows above 2000
The between method :
In the between method, i'm running a while function on all the table and i'm using IF statement to get the right id's here is what i'm doing :
Select * from table
$datastart = $_POST["datastart"];
$dataend = $_POST["dataend"];
$firstid = 0;
$lastid = 0;
$varcount6=1;
$sql = "select ID from users_info";
$sqlread = mysqli_query($conn,$sql);
while($row = mysqli_fetch_assoc($sqlread)){
if($datastart==$varcount6){
$firstid = $rowdirstid["ID"];
}
if($varcount6>=$dataend){
$lastid = $rowdirstid["id1"];
break;
}
$varcount6++;
}
So now i have the first id and the last id of the table, next i use another sql query :
Select * from table where id between $firstid and $lastid
Both worked
My question is: what should i use if i'm loading huge amount of data each time ?
Should i go with while ? or the LIMIT will make the job done ?
To begin with, you should never use PHP to get the data required, stick to doing that solely in SQL, as PHP is never needed.
The limit query you're using will not cut it for what you're trying to do, as it will not care what id's the entries has, so, if your id's are not 100% consecutive, you will not get the desired result.
You should use the between query you display at the bottom of your post.
But, since you haven't provided your full code I cannot say wether or not you sanitized that input, but that is always a good thing to keep in mind. It's preferable to use parameterized queries instead aswell.
If your sure the ID are consecutive, use SELECT * FROM t WHERE id BETWEEN a AND b ORDER BY ID ASC
If you use LIMIT, the SQL Engine have to scan and order all the first results.
(and index the id field)
During fetching data from database with $result = mysqli_query($con,"select * from MY_table, it display 100 columns at a time. my main aim is to display 10 columns at a time, with the help of next and previous buttons user gonna read remaining. is it possible to do with Javascript , or AJAX, or PHP alone.
The word you're looking for is 'pagination'. You can divide your query results into pages. PHP can fetch a part of the query results, and you can click on a button or link to fetch the next page. That next page can be loaded by an entire page refresh, or by Ajax. In either case, PHP fetches the next results and returns them.
9lessons.info has a tutorial on this exact same topic. Well, more a bunch of snippets than a tutorial, but still..
If you're just starting: forget about Ajax at first. Start with reading about the LIMIT clause in MySQL. It allows you to query a subresult of the query, by limiting the returned rows to a specific range.
You can pass a page (or a range) in the url, so when you click 'Next page', you can just call PHP again with ?page=2 or something in the url. Based on that number, you can query a different range of rows.
The last step is to update only a part of the page using Ajax instead of doing a full page refresh.
You can use limit to your sql query to do this
$start = 0;
$result = mysqli_query($con,"select * from MY_table limit ".$start.", 10");
initially $start will be 0 the change the $start variable as per your prev next ..
So I'm trying to find a way to return a very large result set from a query, and display it as a paginated table on a web page.
For example, if I am trying to return 1,000 items from my database, I'd like to display them in a paginated table, 100 at a time, and only query those 100 items.
When a user enters a name to query in a search box, I'd like them to be able to click through the table paginations, where each pagination only queries for 100 items, so 'page' 1 displays items 1-100, 'page' 2 displays items 101-200, etc...
I'd like to do this because querying a very large result set and then just paginating the display is very slow.
Does anyone have any advice on how to do this using PHP and MySQL?
I have the Pagination working fine, I just can't figure out how to run my queries.
Here is the query I have now:
mysql_query("SELECT name, age, address FROM users WHERE name='$name' AND domain_name='$age' LIMIT 100", $localDB);
How do I use this query to return only resultset 101-200, 201-300, etc...?
If you already know the quantities (numbers) for the pagination, then just put a limit on your SQL.
Example using PDO:
//url passed has a token of &page=[digit]
//Do prior error checking to verify $_GET/POST has a page variable, and it is a digit.
if ($page < 1) { $page = 1;}
$offset=$limit*($page-1); // Will give an offset of 100 on page 1, or 200 on page 2, etc
$sql = "SELECT `items` FROM items_db WHERE itemno=:itemno LIMIT :offset, 100";
$sql_query = $conn->prepare($sql); // Existing connection
$sql_query->bindParam(':itemno',$itemno, PDO::PARAM_INT);
$sql_query->bindParam(':offset', $offset, PDO::PARAM_INT);
$sql_query->execute();
Try to using "LIMIT" in your Query
eg:
$query. "LIMIT 0,100"
This will help you to limit your query result. Instead of getting all row you can limit as per your requirement.
I have been reading about speed issues in relation to getting a random row via MYSQL and PHP, and wondered how my code might be improved for speed.
I have banner information in my database in a table called "banners" and i want to display a random banner in relation to the position on the page, and add +1 to the view_count for that banner. My method works, but for a busy site where this happens on each page load, can this be improved for speed? Thanks
/* Get banners for position 1 then choose a random one to display */
$banners = mysql_query("SELECT id,title,banner_url,destination FROM ".TBL_BANNERS." WHERE position = '1' AND status = '1'");
$banner_count = mysql_num_rows($banners) - 1;
$rand_offset = mt_rand(0,$banner_count);
$result = mysql_query("SELECT id,title,banner_url,destination FROM ".TBL_BANNERS." LIMIT $rand_offset, 1 ");
$banner_id = mysql_result($result,0,"id");
$banner_title = mysql_result($result,0,"title");
$banner_url = mysql_result($result,0,"banner_url");
$banner_dest = mysql_result($result,0,"destination");
/* Add view to this banner */
$database->addViewToBanner($banner_id);
The last function uses the query:
"UPDATE banners SET view_count = view_count+1 WHERE id = '$banner_id'"
I also need to say, that there probably wont be any more than 100 records in the "banners" table at any one time but there will be holes in the ID. The IDs might go up to say 200 but only half of those will still exist.
Generate a random number in php and drill it that way into the PK
The SQL would be
SELECT id,title,banner_url,destination
FROM TBL_BANNERS
WHERE id = $rand_offset
If you miss, run it again. This gives a very efficient seek to one row which will be better than using limit/offset processing
The ideal way to do it, as you can read in lots of places around the internet, e.g. Anton Titov's blog is to do 2 queries:
SELECT COUNT(*) AS banners FROM quotes
Then generate a random number in your programming language (i.e. PHP use mt_rand). and feed it into this Query:
SELECT * FROM banners LIMIT $generated_number, 1
NOTE: this isn't good to use if your table only has a small number of rows. Generally I still use ORDER BY RAND() up until I know there are going to be more than 100 rows in the table.
Instead of the first SELECT, use this:
$banners_count_result = mysql_query("SELECT COUNT(*) AS num_banners FROM ".TBL_BANNERS." WHERE position = '1' AND status = '1'");
$banner_count = mysql_result($banners_count_result, 0, "num_banners");
Unless you add and remove new banners every couple of seconds, consider caching this result somewhere.