I would like to know how to update my database table with new data but having the latest data be at the top with the unique id starting at 1. Here's what I mean:
First insert query, for example, inserts 3 article topics:
id article
1 firstNews
2 secondNews
3 thirdNews
Then the next time I run a Cron job to check for new articles, for example two new articles appear, I want the two new articles to be in the beginning of the table, like this:
id article
1 NewArticle1
2 NewArticle2
3 firstNews
4 secondNews
5 thirdNews
Hope that made sense. This might be a bad way to do it, I guess I could have a column with insert date() and then get the data out OrderBy date but it has to be an easier way to do this. I think this would be the easiest to output the most recent data from the table...
If I do ORDER BY DESC, it would output NewArticle2 before NewArticle1, which would defeat the purpose...
id article
1 firstNews
2 secondNews
3 thirdNews
4 NewArticle1
5 NewArticle2
So by DESC, id 5 would be the first one output...I was really hoping there was a way around this...
You should never do this. Just insert at the end, and to get the latest articles, use a query:
SELECT * FROM articles ORDER BY id DESC;
In general: Don't fit the data to your query, fit the query to your data. The id is not a position or number, it uniquely identifies that row of data.
You could use a Date columns and sort on that. Or just sort by ID descending.
It's rarely a good idea to change a PK in place. Not least, you mah have child tables using that PK and maybe history tables too
Note that there is no implicit order to a SQL table: you always need an ORDER BY to guarantee the resultset order
You should add another column specifically for sorting, e.g. a date. and add an INDEX on it.
Then the query becomes:
SELECT *
FROM news
ORDER BY newsdate DESC
Latest news comes first
If there are two news items that could be posted at exactly the same time, you may wish to include a secondary sort:
ORDER BY newsdate DESC, id ASC
It shouldn't be your concern at all.
ID is not a number nor a position by any means. It's just an unique identifier.
Means every database row sticks to it's id forever. While you want to assign your "unique" id to the every newcoming news, which makes no sense.
So, just have usual autoincremented id and select it using ORDER BY id DESC to have latest entries first.
Related
I am making a site which allows admins to basically add points for a user.
At this point in time, I have a table, where id_child is unique, and id_points changes. So a constant stream of id_points can come in, however, it will only show the latest id_points, not the total.
I am wondering how I could go about creating a PHP script that could add all of those together.
From the image, the idea is that I want all id_points values added together to give a total, and this is for the same id_child
Use SQL sum() funciton:
select sum(id_points) from table `table_name` where `id_child` = 1
Hope i understood right.
First if you want to show only the latest points added you have to create another table #__points where you will keep every new change of points.
You need 3 columns id as PRIMARY and AUTO_INCRENMENT , pts and user_id . user_id will be FK to id_child.
So when you want to add a new record :
INSERT INTO `#__points` (pts,user_id) VALUES ("$pts",$id)
When you want to select last inserted value for each admin :
SELECT * from `#__points` where user_id=$id ORDER BY id ASC LIMIT 1
I have a table with data relating to a user, and two important columns:
refer_count, which is updated when a new entry is made in the table with the referred_by column set to that users user_id, and referred_by which is the user_id of the of the user that referred them.
I want to select the users from the table that have the highest number of referrals after a certain date.
For example:
If there are 3 users, one of which referred the other 2 (lets say users 2 and 3), however user 2 was referred on the 2/12/14, whereas user 3 was referred on the 3/1/15.
If the cutoff is 1/12/14, then user 1 is returned with refer_count set to 2, but if the cutoff is after 2/12/14, then user 1 is returned with refer_count set to 1.
I've been thinking of how to do this, but I can't think of a way that would work. Is there a way?
This is via MySQL.
EDIT: I think I may need to provide for information.
The date registered (register_date) is used as the refer date. I need the refer_count to be updated with the number of users referred after the cutoff, however I need to get the actual user. This is for a 'top referrers' table. I can't figure out why I'm having so much trouble thinking of a way to do this.
SELECT user_id FROM usertable WHERE (referal_date BETWEEN '2014-12-2' AND CURDATE())ORDER BY refer_count DESC;
That's the rough idea.
You should look into normalizing your tables if you're keeping that all in the same table, though. It'd be better to keep referals in a seperate table.
Get the row with the maximum in refer_count with a Date condition for your referal_date such that it's after the certainDate:
SELECT user_id FROM table WHERE refer_count = (SELECT MAX(refer_count) FROM table) AND referal_date>certainDate;
Note that WHERE is before SELECT so it will not get the highest count first, but will filter with the date condition then get the highest count.
Edit: Updated query based on edited question.
I have question, I want to insert new row to db (mysql) using php and I need to add it to first place in table, but it comes to last position.
I need to short it like this:
3
2
1
but it shorts like
1
2
3
Can you help me please?
Thanks a lot, Stepan
Assuming that you are using an incremental ID as the unique key, you can do:
order by id desc
if not, you can add a column to the DB called "created" which would be a datetime that you set to NOW() when you create the row. Then you would do:
order by created desc
SQL databases do not guarantee an order, unless you specify an ORDER BY clause.
If you have an identifier column, then you can do:
SELECT ...
FROM your_table
ORDER BY id DESC
I'm trying to get 4 random results from a table that holds approx 7 million records. Additionally, I also want to get 4 random records from the same table that are filtered by category.
Now, as you would imagine doing random sorting on a table this large causes the queries to take a few seconds, which is not ideal.
One other method I thought of for the non-filtered result set would be to just get PHP to select some random numbers between 1 - 7,000,000 or so and then do an IN(...) with the query to only grab those rows - and yes, I know that this method has a caveat in that you may get less than 4 if a record with that id no longer exists.
However, the above method obviously will not work with the category filtering as PHP doesn't know which record numbers belong to which category and hence cannot select the record numbers to select from.
Are there any better ways I can do this? Only way I can think of would be to store the record id's for each category in another table and then select random results from that and then select only those record ID's from the main table in a secondary query; but I'm sure there is a better way!?
You could of course use the RAND() function on a query using a LIMIT and WHERE (for the category). That however as you pointed out, entails a scan of the database which takes time, especially in your case due to the volume of data.
Your other alternative, again as you pointed out, to store id/category_id in another table might prove a bit faster but again there has to be a LIMIT and WHERE on that table which will also contain the same amount of records as the master table.
A different approach (if applicable) would be to have a table per category and store in that the IDs. If your categories are fixed or do not change that often, then you should be able to use that approach. In that case you will effectively remove the WHERE from the clause and getting a RAND() with a LIMIT on each category table would be faster since each category table will contain a subset of records from your main table.
Some other alternatives would be to use a key/value pair database just for that operation. MongoDb or Google AppEngine can help with that and are really fast.
You could also go towards the approach of a Master/Slave in your MySQL. The slave replicates content in real time but when you need to perform the expensive query you query the slave instead of the master, thus passing the load to a different machine.
Finally you could go with Sphinx which is a lot easier to install and maintain. You can then treat each of those category queries as a document search and let Sphinx randomize the results. This way you offset this expensive operation to a different layer and let MySQL continue with other operations.
Just some issues to consider.
Working off your random number approach
Get the max id in the database.
Create a temp table to store your matches.
Loop n times doing the following
Generate a random number between 1 and maxId
Get the first record with a record Id greater than the random number and insert it into your temp table
Your temp table now contains your random results.
Or you could dynamically generate sql with a union to do the query in one step.
SELECT * FROM myTable WHERE ID > RAND() AND Category = zzz LIMIT 1
UNION
SELECT * FROM myTable WHERE ID > RAND() AND Category = zzz LIMIT 1
UNION
SELECT * FROM myTable WHERE ID > RAND() AND Category = zzz LIMIT 1
UNION
SELECT * FROM myTable WHERE ID > RAND() AND Category = zzz LIMIT 1
Note: my sql may not be valid, as I'm not a mySql guy, but the theory should be sound
First you need to get number of rows ... something like this
select count(1) from tbl where category = ?
then select a random number
$offset = rand(1,$rowsNum);
and select a row with offset
select * FROM tbl LIMIT $offset, 1
in this way you avoid missing ids. The only problem is you need to run second query several times. Union may help in this case.
For MySQl you can use
RAND()
SELECT column FROM table
ORDER BY RAND()
LIMIT 4
What SQL query would I use to display the newest entry?
Details:
id is the primary field. I have other fields but that are not related to when they were added.
ORDER BY SomeColumn DESC
LIMIT 1
or
use the MAX() function
Since you didn't give any details about your table it is hard to answer
SELECT * from yourTable ORDER BY `id` DESC LIMIT 1;
Another (better) way would be to have a "date_added" column (date_added TIMESTAMP DEFAULT CURRENT_TIMESTAMP) so you could order by that column descending instead. Dates are more reliable than ID-assignment.
not sure if this is what your looking for but I use mysql_insert_id() after inserting a new row
The auto incremented ID columns are not always the latest records inserted, I've remember really painful experience with this behavior. Conditions where specific, it was mysql 4.1.x at the time and there was almost 1 million records, where 1 out of 3 deleted everiday, and others re inserted in the next 24hours. It made a huge mess when I realize ordering them via ID was not ordering them by age....
Since then, I use a specific column for doing age related sorts, and populating these fields with date = NOW() at each row insert.
Of course it will work to found the latest record as you want, doing an ORDER BY date DESC LIMIT 0,1on your query
SELECT Primary_Key_Field FROM table ORDER BY Primary_Key_Field DESC LIMIT 1
Replace Primary_Key_Field and table obviously :)