I have two tables, one holds the information of contributors to my site and one holds information on photographs contributed.
For the admin side of the site, I want to create a table using php and mysql that displays all contributors but also counts the number of photographs each contributor has available for the site.
I get the list of names using this code
SELECT *
FROM site_con
ORDER BY surn ASC
I have then set up a loop to list all the names but have added a query within that loop to count the number of photographs using this code
$contributor = $row_rsContrib['con_Code'];
mysql_select_db($database_connGrowl, $connGrowl);
$query_rsCounter = "SELECT COUNT(*) AS Count
FROM site_phts
WHERE photter = $contributor";
$rsCounter = mysql_query($query_rsCounter, $connGrowl) or die(mysql_error());
$row_rsCounter = mysql_fetch_assoc($rsCounter);
$totalRows_rsCounter = mysql_num_rows($rsCounter);
The only problem is when '$contributor' is not in the photographs table, it returns an error.
Any ideas?
You can get the list of contributors & the number of photos in a single query:
SELECT sc.*,
COALESCE(x.numPhotos, 0) AS numPht
FROM SITE_CON sc
LEFT JOIN (SELECT sp.photter,
COUNT(*) AS numPhotos
FROM SITE_PHTS sp
GROUP BY sp.photter) x ON x.photter = sc.con_code
ORDER BY ssc.surn
Your query fails because a photographer doesn't necessarily have contributions -- the query above returns the list of photographers, and those without photos associated will have a numPht value of zero. Here's a primer on JOINs, to help explain the OUTER JOIN that's being used.
Actually the best way to do this is by using MSQL to count rather than PHP:
SELECT site_con.*, COUNT( photo_id )
FROM site_con
LEFT JOIN site_phts ON site_con.con_Code = site_phts.photter
GROUP BY site_con.con_Code
ORDER BY site_con.surn
The LEFT JOIN has the special property of creating NULL entries when there is no row in the right table (photos) that matches a contributor row. COUNT will not count these NULL entries. (You need some unique column in the photos table, I used photo_id for that.)
this is the relation between Contributors and photographs:
1 photograph can have a most 1 Contributor
1 Contributor can have a most infinit photograph
Contributor <-(0,n)------(0,1)-> Photograph
so you might wanna add a connexion betweet those two tables, I mean you add the con_id to the photographs table (as a column).
this way you'll be able to retrieve all the informations in one SQL query.
(like OMG Ponies just said)
Do something like this, I believe this should work :
$result = mysql_query("SELECT COUNT(*) AS Count FROM site_phts WHERE photter = '$contributor'"); // put the single quote if $contributor is a string value
//use mysql_fetch_array
if ($row = mysql_fetch_array($result, MYSQL_NUM)) {
printf("ID: %d", $row[0]);
}
Hopefully this works, Good luck mate !
Related
Lets start by saying that I cant use INDEXING as I need the INSERT, DELETE and UPDATE for this table to be super fast, which they are.
I have a page that displays a summary of order units collected in a database table. To populate the table an order number is created and then individual units associated with that order are scanned into the table to recored which units are associated with each order.
For the purposes of this example the table has the following columns.
id, UID, order, originator, receiver, datetime
The individual unit quantities can be in the 1000's per order and the entire table is growing to hundreds of thousands of units.
The summary page displays the number of units per order and the first and last unit number for each order. I limit the number of orders to be displayed to the last 30 order numbers.
For example:
Order 10 has 200 units. first UID 1510 last UID 1756
Order 11 has 300 units. first UID 1922 last UID 2831
..........
..........
Currently the response time for the query is about 3 seconds as the code performs the following:
Look up the last 30 orders by by id and sort by order number
While looking at each order number in the array
-- Count the number of database rows that have that order number
-- Select the first UID from all the rows as first
-- Select the last UID from all the rows as last
Display the result
I've determined the majority of the time is taken by the Count of the number of units in each order ~1.8 seconds and then determining the first and last numbers in each order ~1 second.
I am really interested in if there is a way to speed up these queries without INDEXING. Here is the code with the queries.
First request selects the last 30 orders processed selected by id and grouped by order number. This gives the last 30 unique order numbers.
$result = mysqli_query($con, "SELECT order, ANY_VALUE(receiver) AS receiver, ANY_VALUE(originator) AS originator, ANY_VALUE(id) AS id
FROM scandb
GROUP BY order
ORDER BY id
DESC LIMIT 30");
While fetching the last 30 order numbers count the number of units and the first and last UID for each order.
while($row=mysqli_fetch_array($result)){
$count = mysqli_fetch_array(mysqli_query($con, "SELECT order, COUNT(*) as count FROM scandb WHERE order ='".$row['order']."' "));
$firstLast = mysqli_fetch_array(mysqli_query($con, "SELECT (SELECT UID FROM scandb WHERE orderNumber ='".$row['order']."' ORDER BY UID LIMIT 1) as 'first', (SELECT UID FROM barcode WHERE order ='".$row['order']."' ORDER BY UID DESC LIMIT 1) as 'last'"));
echo "<td align= center>".$count['count']."</td>";
echo "<td align= center>".$firstLast['first']."</td>";
echo "<td align= center>".$firstLast['last']."</td>";
}
With 100K lines in the database this whole query is taking about 3 seconds. The majority of the time is in the $count and $firstlast queries. I'd like to know if there is a more efficient way to get this same data in a faster time without Indexing the table. Any special tricks that anyone has would be greatly appreciated.
Design your database with caution
This first tip may seems obvious, but the fact is that most database problems come from badly-designed table structure.
For example, I have seen people storing information such as client info and payment info in the same database column. For both the database system and developers who will have to work on it, this is not a good thing.
When creating a database, always put information on various tables, use clear naming standards and make use of primary keys.
Know what you should optimize
If you want to optimize a specific query, it is extremely useful to be able to get an in-depth look at the result of a query. Using the EXPLAIN statement, you will get lots of useful info on the result produced by a specific query, as shown in the example below:
EXPLAIN SELECT * FROM ref_table,other_table WHERE ref_table.key_column=other_table.column;
Don’t select what you don’t need
A very common way to get the desired data is to use the * symbol, which will get all fields from the desired table:
SELECT * FROM wp_posts;
Instead, you should definitely select only the desired fields as shown in the example below. On a very small site with, let’s say, one visitor per minute, that wouldn’t make a difference. But on a site such as Cats Who Code, it saves a lot of work for the database.
SELECT title, excerpt, author FROM wp_posts;
Avoid queries in loops
When using SQL along with a programming language such as PHP, it can be tempting to use SQL queries inside a loop. But doing so is like hammering your database with queries.
This example illustrates the whole “queries in loops” problem:
foreach ($display_order as $id => $ordinal) {
$sql = "UPDATE categories SET display_order = $ordinal WHERE id = $id";
mysql_query($sql);
}
Here is what you should do instead:
UPDATE categories
SET display_order = CASE id
WHEN 1 THEN 3
WHEN 2 THEN 4
WHEN 3 THEN 5
END
WHERE id IN (1,2,3)
Use join instead of subqueries
As a programmer, subqueries are something that you can be tempted to use and abuse. Subqueries, as show below, can be very useful:
SELECT a.id,
(SELECT MAX(created)
FROM posts
WHERE author_id = a.id)
AS latest_post FROM authors a
Although subqueries are useful, they often can be replaced by a join, which is definitely faster to execute.
SELECT a.id, MAX(p.created) AS latest_post
FROM authors a
INNER JOIN posts p
ON (a.id = p.author_id)
GROUP BY a.id
Source: http://20bits.com/articles/10-tips-for-optimizing-mysql-queries-that-dont-suck/
I have a pretty simple query,
$query3 = $db->query("SELECT * FROM mybb_ranks WHERE id='1' ORDER by points DESC");
And what it'll return is a database of people who are registered and ranked. Since players points can be randomly changing due to matches, we determine the rank # by assigning it once the value is fetched in a way like this:
$i = 1;
while($row = mysqli_fetch_array($query5))
{
echo "$row[player]'s rank is $i";
$i++;
}
As you can see, it orders the player's by their points, but determines the rank # from a variable that adds after displaying every rank. However, in each of the user profiles, I would like to display their rank as well. This is a bit more difficult, because I need a certain way to count the amount of rows the query has to go through in order to get to the certain player. So for instance, if PlayerB is ranked at #5, I would need a way to display that on his own profile. For this to happen, I imagine the query would need to be altered to be able to count each individual row (4 rows) before it reaches the certain player on the 5th row. I was wondering, how would I go about this?
Try this:
UPDATE mybb_ranks
LEFT JOIN (
SELECT
player,
#rank:=#rank+1 as current_rank
FROM mybb_ranks
WHERE id='1'
ORDER BY points DESC
) AS t
ON mybb_ranks.player = t.player
SET mybb_ranks.rank = t.current_rank
That means you have to create additional column rank in your mybb_ranks table.
This query will update the rank of user each time you generate your ranks list.
So when you need to show user's rank in his profile page you just request it from the table:
SELECT rank
FROM mybb_ranks
WHERE player = :player_id
if you want it more dynamic, you can run this UPDATE query every time when you generate your player profile page, right before SELECT rank.
I try to use different columns within different tables.
Like I want it to run the query If or Where [table.column]
users.username = 'ExampleUsername' AND users.cardnumber = ''
I don't think I can use NULL instead of '', because its an empty text string?
users.cardnumber = NULL
Anyways, I couldn't come further as this:
INSERT INTO users (cardnumber, hasone)
WHERE users.username = 'ExampleName' AND users.cardnumber = ''
SELECT number, sethasone
FROM cards
WHERE cards.used = '0'
LIMIT 1
I'm a bit of new with SQL, but after I got it right I could put the code into my php script.
-
SOLVED! :
I've used two queries for each column.
update users
set hasone=(select sethasone from cards where used='0' LIMIT 1)
where username='TestUser'
and
update users
set cardnumber=(select number from cards where used='0' LIMIT 1)
where username='TestUser'
then I just deleted the row from cards and I was done.
delete from cards
where used = '1'
LIMIT 1
I gave the user a cardnumber from the table cards and delete that row in cards.
I think you are trying to write a nested query but you didn't know how to write it. If you want to write select query within insert or update query so before doing this Click here to read about sub-query or nested query.
Well, I think that you're trying to re-create a JOIN between 2 table. What you need to do is to add a "card_id" field into the users table. Then to get the user AND the card you can do something like :
SELECT * FROM users u LEFT JOIN cards c ON c.id = u.card_id
I have two database tables that I am using to create a Twitter-style following system.
sh_subscriptions
=> id
=> user_id
=> feed_id
sh_feeds
=> id
=> item
=> shop_name
=> feed_id
The problem with storing feed_id rather than shop_name in sh_subscriptions is that it requires a lot of table joining:
$id = $_POST['id'];
$user_id = $id['id'];
$shop_name = mysqli_escape_string($con, $_POST['shop_name']);
$query = "SELECT * FROM sh_subscriptions s INNER JOIN sh_feeds f ON s.feed_id = f.feed_id WHERE s.user_id = $user_id AND f.shop_name = '$shop_name'";
$result = mysqli_query($con, $query) or die(mysqli_error($con));
if (mysqli_num_rows($result) > 0)
{
$query2 = "DELETE FROM sh_subscriptions s INNER JOIN sh_feeds f ON s.feed_id = f.feed_id WHERE s.user_id = $user_id AND f.shop_name = '$shop_name'";
$result2 = mysqli_query($con, $query2) or die(mysqli_error($con));
}
else
{
// insert the row instead
}
(I know there's an error somewhere in the if statement, but I'll worry about that later.)
If I were to replace feed_id with shop_name, I would be able to replace line 5 with this:
$query = "SELECT * FROM sh_subscriptions WHERE user_id = $user_id AND shop_name = '$shop_name'";
My question is: is it always preferable to store MySQL values as integers where possible, or in a situation like this, would it be faster to have sh_subscriptions contain shop_name rather than feed_id?
Your sh_subscriptions table is actually a many-to-many join table that relates users to feeds. This is considered a fine way to design database schemas.
Your basic concept is this: you have a collection of users and a collection of feeds. Each user can subscribe to zero or more feeds, and each feed can have zero or more subscribers.
To enter a subscription you create a row in the sh_subscriptions table. To cancel it you delete the row.
You say there's "a lot of table joining." With respect, this is not a lot of table joining. MySQL is made for this kind of joining, and it will work well.
I have some suggestions about your sh_subscriptions table.
get rid of the id column. Instead make the user_id and feed_id columns into a composite primary key. That way you will automatically prevent duplicate subscriptions.
add an active column ... a short integer ... to the table. When it is set to a value of 1 your suscription is active. That way you can cancel a subscription by setting active to 0.
you might also add a subscribed_date column if you care about that.
create two compound non unique indexes (active,user_id,feed_id) and (active,feed_id,userId) on the table. These will greatly accelerate queries that join tables like this.
Query fragment:
FROM sh_feed f
JOIN sh_subscription s ON (f.feed_id = s.feed_id AND s.active = 1)
JOIN sh_users u ON (s.user_id = u.user_id)
WHERE f.shop_name = 'Joe the Plumber'
If you get to the point where you have hundreds of millions of users or feeds, you may need to consider denormalizing this table.. that is, for example, relocating the shop name text so it's in the sh_subscriptions table. But not now.
Edit I am proposing multiple compound covering indexes. If you're joining feeds to users, for example, MySQL starts satisfying your query by determining the row in sh_feeds that matches your selection.
It then determines the feed_id, and random-accesses your compound index on feed_id. Then, it needs to look up all the user_id values for that feed_id. It can do that by scanning the index from the point where it random-accessed it, without referring back to the table. This is very fast indeed. It's called a covering index.
The other covering index deals with queries that start with a known user and proceed to look up the feeds. The order of columns in indexes matters: random access can only start with the first (leftmost) column of the index.
The trick to understand is that these indexes are both randomly accessible and sequentially scannable.
one other note If you only have two columns in the join table, one of your covering indexes is also your primary key, and the other contains the columns in the reverse order from the primary key. You don't need any duplicate indexes.
I am joining 2 tables and trying to display the results. Only problem is every result is duplicated. I have 2 tables, messages and follow. Messages are what a certain user inputs, and I want it to display only to the people that follow that certain user.
Messages | Follow
-id -id
-message -mem1 (logged in user)
-userid -mem2 (followed user)
-created
$display ="";
$sql = mysql_query("
SELECT * FROM messages AS me
JOIN follow AS fl
ON me.userid = fl.mem2
WHERE fl.mem1 = $id (logged in user)
ORDER BY me.created
DESC LIMIT 10
") or die(mysql_error());
while($row=mysql_fetch_array($query)){
$msgid = $row["id"];
$message = $row["message"];
$userid = $row["userid"];
$created = $row["created"];
$display .="<?php echo $userid; ?> : <?php echo $message; ?><br />
<?php echo $created; ?>";
}
In the database there are no duplicates, just on the retrieve. Thanks for the input!
Edited: Display Code
You're getting "double" results, most likely because the query results in something different then you expect.
If I understand your table-structure correctly; you have a one-to-many relation from messages to followers.
In your query, however, you fetch combinations of messages and followers. Each line will consist of a unique combination of message<>follower.
In short; when a single message has two followers, you'll get two rows in the result with the same message; but a different follower entry.
If you want to show each message once; and then list all followers per message you can either use group-by functions (e.g group_concat) and group-by on message entries. The other possibility is to fetch the followers in a separate query once you've retrieved the message row, and then print the results from that query as the followers for that message.
If you're simply trying to get the number of followers; you can use a group-by on the UID of your message table and add a count on the UID or user ID of the follower table. (Do not that with group-by, the select * from shouldn't be used; but separate columns can.)
There's really only a few things that could cause the records to duplicate - try breaking down the query into basic components to see if there are more than one record:
SELECT * FROM follow WHERE mem1 = [id];
SELECT * FROM messages WHERE userid = [mem2 from previous result];
If either of the previous statements return more than one record, than the problem lies there. Other than that, I'd look at the PHP code to see if you're doing something there.
As for the query itself, I have a few recommendations:
Place the table with the filter first - the sooner you can narrow the results the better.
Specify a field list instead of using '*' - this will be a tiny bit more efficient, and clarify what you're after. Also, it will give 'DISTINCT' a fighting chance to work...
Here's an example:
SELECT DISTINCT me.id, me.message, me.userid, me.created
FROM follow AS fl
INNER JOIN messages AS me ON me.userid = fl.mem2
WHERE fl.mem1 = :logged_in_user
ORDER BY me.created
DESC LIMIT 10
If you are sure that there are no duplicates and the problem is in the query (you can check that by executing it from your database's interface), you can try two things:
Use the follow table as the leading one:
SELECT messages.*
FROM follow
JOIN messages ON follow.mem2=messages.userid
WHERE follow.mem1=$id
ORDER BY messages.created DESC
LIMIT 0,10;
Use a subquery:
SELECT *
FROM messages
WHERE userid IN(
SELECT DISCTINCT(mem2)
FROM follow
WHERE mem1=$id
)
ORDER BY created DESC
LIMIT 0,10;