What I'm basically trying to do is get the the staff table, fetch the id of the names per job title and then hit another table (based on the id fetched) and get the data I'm interested in off.
My approach so far is make a query, go with a while loop to get all the ids of the job title im interested and for every id go with another loop ( connection-query) to subtract more data.
I think my approach is wrong cause im suspicious i could merge those two queries into one not sure how though.
//new db connection here... (1)
$query="SELECT * FROM staff WHERE jobtitle='$forEachJob'";
$result=mysql_query($query);
while ($row = mysql_fetch_assoc($result)) {
$idFetched = $row['id'];
//new db connection here... (2)
$nextQuery = "SELECT * FROM schedule WHERE name='$idFetched' ORDER BY Day asc";
$nextResult = mysql_query($nextQuery)
}
You want to do a JOIN in mysql:
SELECT * FROM staff
JOIN schedule ON schedule.name = staff.id
WHERE jobtitle = '$forEachJob'
ORDER BY Day ASC
By the way, avoid using SELECT * and look into a DB wrapper such as PDO to sanitize/prepare your queries.
Related
I have the following two queries. The first query is fetching a key called srNumber from first table called tags and then the second query is using that srNumber to fetch details from a second table called nexttable.
$tagQuery = "SELECT * FROM tags WHERE status = 0 AND currentStage = '1' AND assignedTo = '1' ORDER BY
deliveryDate ASC";
$tagQueryExecute = mysqli_query($conn, $tagQuery);
while($rows = mysqli_fetch_array($tagQueryExecute)){
$srNumber = $rows['srNumber'];
$nextQuery = "SELECT * FROM nexttable WHERE srNumber='$srNumber'";
$nextQueryExecute = mysqli_query($conn, $nextQuery);
$detailsFromNextTable = mysqli_fetch_array($nextQueryExecute);
//Show these details
}
For a small result this is not a big issue. But if the first query got so many results, then second query has to run as many times as number of loop. Is there any other way to do this efficiently?
NB: Please ignore the SQL injection issues with these queries. I just simplified it to show the problem
As you appear to have only 1 row in the second table, you would be better off with a join, MySQL: Quick breakdown of the types of joins gives some more info on the types of joins.
SELECT *
FROM tags t
JOIN nexttable n on t.srNumber = n.srNumber
WHERE t.status = 0 AND t.currentStage = '1' AND t.assignedTo = '1'
ORDER BY t.deliveryDate ASC
This also removes the SQL injection as well.
I would also recommend removing the * and just list the columns you intend to use, this also helps if you have columns with the same names in the different tables as you can add an alias to the specific columns.
FYI - the original problem you have is similar to What is the "N+1 selects problem" in ORM (Object-Relational Mapping)?
I need to synchronize specific information between two databases (one mysql, the other a remote hosted SQL Server database) for thousands of rows. When I execute this php file it gets stuck/timeouts after several minutes I guess, so I wonder how I can fix this issue and maybe also optimize the way of "synchronizing" it.
What the code needs to do:
Basically I want to get for every row (= one account) in my database which gets updated - two specific pieces of information (= 2 SELECT queries) from another SQL Server database. Therefore I use a foreach loop which creates 2 SQL queries for each row and afterwards I update those information into 2 columns of this row. We talk about ~10k Rows which needs to run thru this foreach loop.
My idea which may help?
I have heard about things like PDO Transactions which should collect all those queries and sending them afterwards in a package of all SELECT queries, but I have no idea whether I use them correctly or whether they even help in such cases.
This is my current code, which is timing out after few minutes:
// DBH => MSSQL DB | DB => MySQL DB
$dbh->beginTransaction();
// Get all referral IDs which needs to be updated:
$listAccounts = "SELECT * FROM Gifting WHERE refsCompleted <= 100 ORDER BY idGifting ASC";
$ps_listAccounts = $db->prepare($listAccounts);
$ps_listAccounts->execute();
foreach($ps_listAccounts as $row) {
$refid=$row['refId'];
// Refsinserted
$refsInserted = "SELECT count(username) as done FROM accounts WHERE referral='$refid'";
$ps_refsInserted = $dbh->prepare($refsInserted);
$ps_refsInserted->execute();
$row = $ps_refsInserted->fetch();
$refsInserted = $row['done'];
// Refscompleted
$refsCompleted = "SELECT count(username) as done FROM accounts WHERE referral='$refid' AND finished=1";
$ps_refsCompleted = $dbh->prepare($refsCompleted);
$ps_refsCompleted->execute();
$row2 = $ps_refsCompleted->fetch();
$refsCompleted = $row2['done'];
// Update fields for local order db
$updateGifting = "UPDATE Gifting SET refsInserted = :refsInserted, refsCompleted = :refsCompleted WHERE refId = :refId";
$ps_updateGifting = $db->prepare($updateGifting);
$ps_updateGifting->bindParam(':refsInserted', $refsInserted);
$ps_updateGifting->bindParam(':refsCompleted', $refsCompleted);
$ps_updateGifting->bindParam(':refId', $refid);
$ps_updateGifting->execute();
echo "$refid: $refsInserted Refs inserted / $refsCompleted Refs completed<br>";
}
$dbh->commit();
You can do all of that in one query with a correlated sub-query:
UPDATE Gifting
SET
refsInserted=(SELECT COUNT(USERNAME)
FROM accounts
WHERE referral=Gifting.refId),
refsCompleted=(SELECT COUNT(USERNAME)
FROM accounts
WHERE referral=Gifting.refId
AND finished=1)
A correlated sub-query is essentially using a sub-query (query within a query) that references the parent query. So notice that in each of the sub-queries I am referencing the Gifting.refId column in the where clause of each sub-query. While this isn't the best for performance because each of those sub-queries still has to run independent of the other queries, it would perform much better (and likely as good as you are going to get) than what you have there.
Edit:
And just for reference. I don't know if a transaction will help here at all. Typically they are used when you have several queries that depend on each other and to give you a way to rollback if one fails. For example, banking transactions. You don't want the balance to deduct some amount until a purchase has been inserted. And if the purchase fails inserting for some reason, you want to rollback the change to the balance. So when inserting a purchase, you start a transaction, run the update balance query and the insert purchase query and only if both go in correctly and have been validated do you commit to save.
Edit2:
If I were doing this, without doing an export/import this is what I would do. This makes a few assumptions though. First is that you are using a mssql 2008 or newer and second is that the referral id is always a number. I'm also using a temp table that I insert numbers into because you can insert multiple rows easily with a single query and then run a single update query to update the gifting table. This temp table follows the structure CREATE TABLE tempTable (refId int, done int, total int).
//get list of referral accounts
//if you are using one column, only query for one column
$listAccounts = "SELECT DISTINCT refId FROM Gifting WHERE refsCompleted <= 100 ORDER BY idGifting ASC";
$ps_listAccounts = $db->prepare($listAccounts);
$ps_listAccounts->execute();
//loop over and get list of refIds from above.
$refIds = array();
foreach($ps_listAccounts as $row){
$refIds[] = $row['refId'];
}
if(count($refIds) > 0){
//implode into string for use in query below
$refIds = implode(',',$refIds);
//select out total count
$totalCount = "SELECT referral, COUNT(username) AS cnt FROM accounts WHERE referral IN ($refIds) GROUP BY referral";
$ps_totalCounts = $dbh->prepare($totalCount);
$ps_totalCounts->execute();
//add to array of counts
$counts = array();
//loop over total counts
foreach($ps_totalCounts as $row){
//if referral id not found, add it
if(!isset($counts[$row['referral']])){
$counts[$row['referral']] = array('total'=>0,'done'=>0);
}
//add to count
$counts[$row['referral']]['total'] += $row['cnt'];
}
$doneCount = "SELECT referral, COUNT(username) AS cnt FROM accounts WHERE finished=1 AND referral IN ($refIds) GROUP BY referral";
$ps_doneCounts = $dbh->prepare($doneCount);
$ps_doneCounts->execute();
//loop over total counts
foreach($ps_totalCounts as $row){
//if referral id not found, add it
if(!isset($counts[$row['referral']])){
$counts[$row['referral']] = array('total'=>0,'done'=>0);
}
//add to count
$counts[$row['referral']]['done'] += $row['cnt'];
}
//now loop over counts and generate insert queries to a temp table.
//I suggest using a temp table because you can insert multiple rows
//in one query and then the update is one query.
$sqlInsertList = array();
foreach($count as $refId=>$count){
$sqlInsertList[] = "({$refId}, {$count['done']}, {$count['total']})";
}
//clear out the temp table first so we are only inserting new rows
$truncSql = "TRUNCATE TABLE tempTable";
$ps_trunc = $db->prepare($truncSql);
$ps_trunc->execute();
//make insert sql with multiple insert rows
$insertSql = "INSERT INTO tempTable (refId, done, total) VALUES ".implode(',',$sqlInsertList);
//prepare sql for insert into mssql
$ps_insert = $db->prepare($insertSql);
$ps_insert->execute();
//sql to update existing rows
$updateSql = "UPDATE Gifting
SET refsInserted=(SELECT total FROM tempTable WHERE refId=Gifting.refId),
refsCompleted=(SELECT done FROM tempTable WHERE refId=Gifting.refId)
WHERE refId IN (SELECT refId FROM tempTable)
AND refsCompleted <= 100";
$ps_update = $db->prepare($updateSql);
$ps_update->execute();
} else {
echo "There were no reference ids found from \$dbh";
}
I have 2 tables, one is called post and one is called followers. Both tables have one row that is called userID. I want to show only posts from people that the person follows. I tried to use one MySQL query for that but it was not working at all.
Right now, I'm using a workaround like this:
$getFollowing = mysqli_query($db, "SELECT * FROM followers WHERE userID = '$myuserID'");
while($row = mysqli_fetch_object($getFollowing))
{
$FollowingArray[] = $row->followsID;
}
if (is_null($FollowingArray)) {
// not following someone
}
else {
$following = implode(',', $FollowingArray);
}
$getPosts = mysqli_query($db, "SELECT * FROM posts WHERE userID IN($following) ORDER BY postDate DESC");
As you might imagine im trying to make only one call to the database. So instead of making a call to receive $following as an array, I want to put it all in one query. Is that possible?
Use an SQL JOIN query to accomplish this.
Assuming $myuserID is an supposed to be an integer, we can escape it simply by casting it to an integer to avoid SQL-injection.
Try reading this wikipedia article and make sure you understand it. SQL-injections can be used to delete databases, for example, and a lot of other nasty stuff.
Something like this:
PHP code:
$escapedmyuserID = (int)$myuserID; // make sure we don't get any nasty SQL-injections
and then, the sql query:
SELECT *
FROM followers
LEFT JOIN posts ON followers.someColumn = posts.someColumn
WHERE followers.userID = '$escapedmyuserID'
ORDER BY posts.postDate DESC
I have 2 tables. One (artWork) with all the data I want to pull from, including 2 cols of id's. The other (sharedWork) has the same 2 id cols that are also in the first -- but none of the essential data I want to echo out. Objective: use the id's in both table to filter out row in the first (artWork). See below in the code what I tried that didn't work
I also tried to figure out an inner join that would accomplish the same. No luck there either. Wondering which would be the best approach and how to do it.
thanks
Allen
//////// Get id's first ///////////
$QUERY0="SELECT * FROM artWork WHERE user_id = '$user_id' ";
$res0 = mysql_query($QUERY0);
$num0 = mysql_num_rows($res0);
if($num0>0){
while($row = mysql_fetch_array($res0)){
$art_id0 = $row['art_id'];
}
}
$QUERY1="SELECT * FROM shareWork WHERE user_id = '$user_id' ";
$res1 = mysql_query($QUERY1);
$num1 = mysql_num_rows($res1);
if($num1>0){
while($row = mysql_fetch_array($res1)){
$art_id = $row['art_id'];
}
}
$art_id2 = array_merge($art_id0, $art_id1);
foreach ($art_id2 as $art_id3){
$QUERY="SELECT * FROM artWork WHERE art_id = '$art_id3' ";
// echo "id..".$art_id0;
$res = mysql_query($QUERY);
$num = mysql_num_rows($res);
if($num>0){
while($row = mysql_fetch_array($res)){
$art_title = $row['art_title'];
$art_id = $row['art_id'];
etc................and so on
.........to....
</tr>";
}
}
}
Don't query your database inside a loop unless you absolutely have to.
Everytime you query the database, you're using disk I/O to read through the database and return your record. Disk I/O is the slowest read on a computer, and will be a massive bottleneck for your application.
If you run larger queries upfront, or at least outside of a loop, you will hit your disk less often, improving performance. Your results from larger queries will be held in memory, which is considerably faster than reading from disk.
Now, with that warning out of the way, let's address your actual problem:
It seems you're trying to grab records from artWork where the user is the primary artist, or the user was one of several artists to work on a group project. artWork seems to hold the id of the primary artist on the project whereas shareWork is probably some sort of many-to-many lookup table which associates user ids with all art projects they were a part of.
The first thing I should ask is whether or not you even need the first query to artWork or if the primary artist should have a record for that art_id in shareWork anyway, for having worked on the project at all.
If you don't need the first lookup, then the query becomes very easy: just grab all of the users art_ids from shareWork table and use that to lookup the his or her records in the main artWork table:
SELECT artWork.*
FROM artWork
WHERE art_id IN
(SELECT art_id
FROM shareWork
WHERE user_id = $user)
If you do need to look in both tables, then you just add a check in the query above to also check for that user in the artWork table:
SELECT artWork.*
FROM artWork
WHERE
user_id = $user
OR art_id IN
(SELECT art_id
FROM shareWork
WHERE user_id = $user)
This will get you all artWork records in a single query, rather than.. well, a lot of queries, and you can do your mysql_fetch_array loop over the results of that one query and be done with it.
Alright, so I have a table outputting data from a MySQL table in a while loop. Well one of the columns it outputs isn't stored statically in the table, instead it's the sum of how many times it appears in a different MySQL table.
Sorry I'm not sure this is easy to understand. Here's my code:
$query="SELECT * FROM list WHERE added='$addedby' ORDER BY time DESC";
$result=mysql_query($query);
while($row=mysql_fetch_array($result, MYSQL_ASSOC)){
$loghwid = $row['hwid'];
$sql="SELECT * FROM logs WHERE hwid='$loghwid' AND time < now() + interval 1 hour";
$query = mysql_query($sql) OR DIE(mysql_error());
$boots = mysql_num_rows($query);
//Display the table
}
The above is the code displaying the table.
As you can see it's grabbing data from two different MySQL tables. However I want to be able to ORDER BY $boots DESC. But as its a counting of a completely different table, I have no idea of how to go about doing that.
There is a JOIN operation that is intended to... well... join two different table together.
SELECT list.hwid, COUNT(log.hwid) AS boots
FROM list WHERE added='$addedby'
LEFT JOIN log ON list.hwid=log.hwid
GROUP BY list.hwid
ORDER BY boots
I'm not sure if ORDER BY boots in the last line will work like this in MySQL. If it doesn't, just put all but the last line in a subquery.
But the result of the query into an array indexed by $boots.
AKA:
while(..){
$boot = mysql_num_rows($query);
$results[$boot][] = $result_array;
}
ksort($results);
foreach($results as $array)
{
foreach($array as ....)
{
// display table
}
}
You can switch between ksort and krsort to switch the orders, but basically you are making an array that is keyed by the number in $boot, sorting that array by that number, and then traversing each group of records that have a specific $boot value.