I am trying to make a social networking site in PHP/MySQL. I am currently developing status update and comments on status's system. I am trying to show all status of mine and comments on certain status. For doing that I have two tables: comment and user_status.
I have used this MySQL query,
SELECT * FROM user_status LEFT JOIN
comment ON id_status = comment.status_id
WHERE sender_id = '$id2'
OR receive_id = '$id2'
/* $id2 is my id */
I have successfully showed status and one comment. But the problem is, when the number of comments are more than one, then the status shows more than one times. How much same status will be showed depends on how much comments available on certain status. But I would like to be able to display same status only one time, and display more than one comments (if available) on certain status.
This isn't so much a PHP problem as it is confusion about how SQL joins work.
It sounds as if what you really want is not so much a join but a distinct set of records from two tables. Until your SQL skils develop a little more, consider simplifying things by making two queries -- one each for comment and user_status. Also consider requesting just the specific fields you're interested rather than using SELECT *.
Here is a visual explanation of different SQL joins, in case you want to pursue this with a single query.
I assume that you are not displaying the raw results from the query, but rather are piping them to an html page to display. Display only the most recent status in a textbox. then display thin a table or list an ordered list of the comments.
Your query is correct.
Related
I've been working on this for some hours now and it's getting tiring. I want to get users posts from people I follow and myself, just like twitter does.
So there's a table users_posts that has all users' posts with column user_id to determine who made the post.
Another table users_followers that contains all followers ie. user_id follows following_id
So here's my query:
User ID = 2271
SELECT users_followers.following_id AS following_id, users_posts.id
FROM users_followers, users_posts
WHERE users_posts.user_id = users_followers.following_id
AND (users_followers.user_id =2271)
This query works but the problem is, it's kinda slow. Is there a faster way to do this?
Also, as you can see, I can only get posts from those I follow, and not myself.
Any help?
If I'm understanding your tables properly, I would do this with an explicit JOIN. I'm not sure how much that would speed things up versus the implicit JOIN you're using though.
SELECT following_id, p.id
FROM users_followers f
LEFT JOIN users_posts p
ON (p.user_id = f.following_id)
WHERE f.user_id = 2271
Chances are, adding an index or two to your tables would help.
Using the MySQL EXPLAIN command (just put it in front of your SELECT query) will show the indexes, temporary tables, and other resources that are used for a query. It should give you an idea when one query is faster or more efficient than another.
Your query is fine as written, provided you have properly indexed your tables. At a minimum you need an index on users_posts.user_id and users_followers.following_id.
A query can also be slowed by large numbers of records, even when it is fully indexed. In that case, I find phpmyadmin to be an invaluable tool. From the server page (maybe localhost) select the Status tab to see a wealth of information about how your mysql server is performing and suggestions for how to improve it.
For a new version of a website, I am making a "Top User" section on the homepage. This allows people to vote for the user on a bunch of different categories. All this information is stored in a MySQL database in two main tables. One table has the information(id*autogenerated*, Username, Date added, etc.) and the other has the rates (id*autogenerated*, linkID, rowAvg, avg, avg2, etc.). The linkID from the rate table corresponds to the id from the information table. How the query works is it queries through the rate_table, orders it by highest averages then selects the first 10 results. Then using the linkID of that row, I select the actual information for that user from the info_table. This is fine and dandy as long as each user only has 1 rate. What happens when a user has 2 or more rates, and both of the rates are positive, is the query selects both of those and pulls the information for each of the 2 rows which is then displayed as two different users even though it is the same person. How can I make the rate_table query know when there are multiple rates for the same linkID and average them together instead of showing them as two different people. I was thinking of inserting each linkID into an array, then for each subsequently selected row, check if that linkID is already in the array. If not, insert it, if it is, then average them together and store it in the array and use the array to populate the table on the homepage. I feel like I am overthinking this. Sorry if this is a little confusing. If you need more information, let me know.
P.S. I'm still learning my way around MySQL queries so I apologize if I am going about this the completely wrong way and you spent the last few minutes trying to understand what I was saying :P
P.P.S. I know I shouldn't be using MySQL_Query anymore, and should be doing prepared statements. I want to master MySQL queries because that is what FMDB databases for iOS use then I will move onto learning prepared statements.
Take a look at some of the MySQL Aggregate Functions.
AVG() may be what you're looking for. The average of one result is just that result, so that should still work. Use the GROUP BY clause on the column that should be unique in order to run the aggregate calculation on the grouped rows.
My PHP application has the function product_fetch([parameters]) which returns 'Product' objects which information are stored in database.
In my admin area, there is a page called "Featured Products" which allows me to select 10 products to be displayed in the main page.
Now comes the problem: I made 10 select/combobox, each allows me to select one product, out of 400. So in order to make all the options, a query has to be made: SELECT * FROM products
Question: Is it correct to make such a query, even though there's hundreds of rows?
The solution you proposed is certainly do-able, and 400 rows is really meek compared to the upper limits of what MySQL is capable of handling. What is more concerning is the user experience here. Granted this will only affect you, but I would design myself something a little nicer than a bunch of <select>s. My idea is to start with just one textbox that autocompletes the names of your products. This can be accomplished if the product title has a fulltext index. Then your autocomplete script could use this query:
SELECT * FROM Products WHERE MATCH(title) AGAINST ('contents of textbox' IN BOOLEAN MODE);
There are plenty of jQuery plugins like Autocomplete that will handle the JS side (querying the server for autocomplete results). The one I just mentioned adds a term GET parameter which you could easily grab and throw into the query:
// You might want to only select the relevant columns
$stmt = $pdo->prepare('SELECT * FROM Products WHERE MATCH(title) AGAINST (:search IN BOOLEAN MODE)');
$stmt->execute(array(':search' => $_GET['term']);
// Output JSON results
echo json_encode($stmt->fetchall());
Once you type in (or click on an autocomplete result) in the one textbox, another should appear below it and the focus should go to it. From there you can type another product, and continue until you reach 10. Each textbox (unless there is only one) should have a delete link next to it that removes that product from the featured listing.
I'll look for a site that implements this kind of functionality so you can better understand what I'm talking about. Basically here, what you're searching for is achieved. You don't have to have 10 select boxes with 400 options and you don't need a SELECT * FROM Products.
You would be much better of specifying which produts you want in the query and only returning those if you have no intention of using any of the others at all.
You can do this using many methods. A simple one would be using an ID field in an in statement like this:
select col1, col2 from products where id in(1,4,12,5)
It might seem to make little difference, but what if your procuts table had a hundred thousand rows in it?
You could also have a flag in the table to say that the items are featured which would let you use something like this:
select col1, col2 from products where featured='Y'
Or you could even have a table that only has featured items (even just their ID) and join it to your main listing like this:
select
a.col1,
a.col2
from
products a
join featured b
on a.id=b.id
If you want to pick through your whole table, you can even use a simple limit clause that picks up a certain number of rows from the table and can be reused to get the next set:
select col1, col2 from products limit 10;
// Will pick the first 10 rows of data.
select col1, col2 from procuts limit 30,10;
// Will pick rows 31-40 (skipping first 30, then returning next 10)
The short version is though, no matter how you do it, pulling back a whole table of data to pick through it within PHP is a bad thing and to be avoided at all costs. It makes the database work much harder, uses more network between the database and PHP (even if they are on the same machine, it is transferring a lot more data between the two of them) and it will by default make PHP use a lot more resources to process the information.
SELECT * FROM tbl LIMIT $page,10;
The above query will select 10 entries from offset $page
Fetching all rows is a bad idea as you are using 10 only anyway. When your table expands to millions of rows, you will see a noticeable difference.
There is nothing fundamentally wrong with selecting all rows if that's what you mean to do. Hundreds of rows also shouldn't be a problem for the query in terms of performance. However, thousands or millions might if your database grows that big.
Think about the user - can they scroll through hundreds of products? Probably. If not, then maybe it's the UI design at fault, not the query.
I am currently using MySQL and MyISAM.
I have a function of which returns an array of user IDs of either friends or users in general in my application, and when displaying them a foreach seemed best.
Now my issue is that I only have the IDs, so I would need to nest a database call to get each user's other info (i.e. name, avatar, other fields) based on the user ID in the loop.
I do not expect hundreds of thousands of users (mainly for hobby learning), although how should I do this one, such as the flexibility of placing code in a foreach for display, but not relying on ID arrays so I am out of luck to using a single query?
Any general structures or tips on what I can display the list appropriately with?
Is my amount of queries (1:1 per users in list) inappropriate? (although pages 0..n of users, 10 at a time make it seem not as bad I just realize.)
You could use the IN() MySQL method, i.e.
SELECT username,email,etc FROM user_table WHERE userid IN (1,15,36,105)
That will return all rows where the userid matches those ID's. It gets less efficient the more ID's you add but the 10 or so you mention should be just fine.
Why couldn't you just use a left join to get all the data in 1 shot? It sounds like you are getting a list, but then you only need to get all of a single user's info. Is that right?
Remember databases are about result SETS and while generally you can return just a single row if you need it, you almost never have to get a single row then go back for more info.
For instance a list of friends might be held in a text column on a user's entry.
Whether you expect to have a small database or large database, I would consider using the InnoDB engine rather than MyISAM. It does have a little higher overhead for processing than MyISAM, however you get all the added benefits (as your hobby grows) including JOIN, which will allow you to pull in specific data from multiple tables:
SELECT u.`id`, p.`name`, p.`avatar`
FROM `Users` AS u
LEFT JOIN `Profiles` AS p USING `id`
Would return id from Users and name and avatar from Profiles (where id of both tables match)
There are numerous resources online talking about database normalization, you might enjoy: http://www.devshed.com/c/a/MySQL/An-Introduction-to-Database-Normalization/
I'm running a sql query to get basic details from a number of tables. Sorted by the last update date field. Its terribly tricky and I'm thinking if there is an alternate to using the UNION clause instead...I'm working in PHP MYSQL.
Actually I have a few tables containing news, articles, photos, events etc and need to collect all of them in one query to show a simple - whats newly added on the website kind of thing.
Maybe do it in PHP rather than MySQL - if you want the latest n items, then fetch the latest n of each of your news items, articles, photos and events, and sort in PHP (you'll need the last n of each obviously, and you'll then trim the dataset in PHP). This is probably easier than combining those with UNION given they're likely to have lots of data items which are different.
I'm not aware of an alternative to UNION that does what you want, and hopefully those fetches won't be too expensive. It would definitely be wise to profile this though.
If you use Join in your query you can select datas from differents tables who are related with foreign keys.
You can look of this from another angle: do you need absolutely updated information? (the moment someone enters new information it should appear)
If not, you can have a table holding the results of the query in the format you need (serving as cache), and update this table every 5 minutes or so. Then your query problem becomes trivial, as you can have the updates run as several updates in the background.