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  • Avoid MySQL multi-results from SP with Execute

    - by hhyhbpen
    Hi, i have an SP like BEGIN DECLARE ... CREATE TEMPORARY TABLE tmptbl_found (...); PREPARE find FROM" INSERT INTO tmptbl_found (SELECT userid FROM ( SELECT userid FROM Soul WHERE .?.?. ORDER BY .?.?. ) AS left_tbl LEFT JOIN Contact ON userid = Contact.userid WHERE Contact.userid IS NULL LIMIT ?) "; DECLARE iter CURSOR FOR SELECT userid, ... FROM Soul ...; ... l:LOOP FETCH iter INTO u_id, ...; ... EXECUTE find USING ...,. . .,u_id,...; ... END LOOP; ... END// and it gives multi-results. Besides it's inconvenient, if i get all this multi-results (which i really don't need at all), about 5 (limit's param) for each of the hundreds of thousands of records in Soul, i'm afraid it will take all my memory (and all in vain). Also, i noticed, if i do prepare from an empty string, it still has multi-results... At least how to get rid of them in the execute statement? And i would like to have a recipe to avoid ANY output from SP, for any possible statement (i also have a lot of "update ..."s and "select ... into "s inside, if they can produce multi's). Tnx for any help...

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  • A better way to delete a list of elements from multiple tables

    - by manyxcxi
    I know this looks like a 'please write the code' request, but some basic pointer/principles for doing this the right way should be enough to get me going. I have the following stored procedure: CREATE PROCEDURE `TAA`.`runClean` (IN idlist varchar(1000)) BEGIN DECLARE EXIT HANDLER FOR NOT FOUND ROLLBACK; DECLARE EXIT HANDLER FOR SQLEXCEPTION ROLLBACK; DECLARE EXIT HANDLER FOR SQLWARNING ROLLBACK; START TRANSACTION; DELETE FROM RunningReports WHERE run_id IN (idlist); DELETE FROM TMD_INDATA_INVOICE WHERE run_id IN (idlist); DELETE FROM TMD_INDATA_LINE WHERE run_id IN (idlist); DELETE FROM TMD_OUTDATA_INVOICE WHERE run_id IN (idlist); DELETE FROM TMD_OUTDATA_LINE WHERE run_id IN (idlist); DELETE FROM TMD_TEST WHERE run_id IN (idlist); DELETE FROM RunHistory WHERE id IN (idlist); COMMIT; END $$ It is called by a PHP script to clean out old run history. It is not particularly efficient as you can see and I would like to speed it up. The PHP script gathers the ids to remove from the tables with the following query: $query = "SELECT id, stop_time FROM RunHistory WHERE config_id = $configId AND save = 0 AND NOT(stop_time IS NULL) ORDER BY stop_time"; It keeps the last five run entries and deletes all the rest. So using this query to bring back all the IDs, it determines which ones to delete and keeps the 'newest' five. After gathering the IDs it sends them to the stored procedure to remove them from the associated tables. I'm not very good with SQL, but I ASSUME that using an IN statement and not joining these tables together is probably the least efficient way I can do this, but I don't know enough to ask anything but "how do I do this better?" If possible, I would like to do this all in my stored procedure using a query to gather all the IDs except for the five 'newest', then delete them. Another twist, run entries can be marked save (save = 1) and should not be deleted. The RunHistory table looks like this: CREATE TABLE `TAA`.`RunHistory` ( `id` int(11) NOT NULL auto_increment, `start_time` datetime default NULL, `stop_time` datetime default NULL, `config_id` int(11) NOT NULL, [...] `save` tinyint(1) NOT NULL default '0', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;

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  • How do I echo out something different when reached last row?

    - by Josh Brown
    I am wanting to not echo out the comma at the end of the echo after the last row. How can I do that? Here is my code: <?php header("Content-type: application/json"); echo '{"points":['; mysql_connect("localhost", "user", "password"); mysql_select_db("database"); $q = "SELECT venues.id, venues.lat, venues.lon, heat_indexes.temperature FROM venues, heat_indexes WHERE venues.id = heat_indexes.venue_id"; $res = mysql_query($q) or die(mysql_error()); while ($point = mysql_fetch_assoc($res)) { echo $point['lat'] . "," . $point['lon'] . "," . $point['temperature'] . ","; } mysql_free_result($res); echo ']}'; ?>

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  • "No database selected" even when db clearly selected

    - by Someone
    One of my webpages gets a recurring error: "No database selected", even though the DB is selected. Right about now it's a 50-50 chance whether the page will load just fine, or whether I receive this error. After one or two reloads, the page works again. I am including the exact same connection file on my other pages, and I don't have this problem. What could be the cause of this? I'm using ensim pro for webhosting. TIA.

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  • Help with grasping (INNER?) JOIN

    - by Greenie
    I'm having trouble building a query. I can do what I want in 3 different queries. SELECT id FROM table1 WHERE url LIKE '%/$downloadfile' put that in $url_id SELECT item_id FROM table2 WHERE rel_id = '$url_id'" put that in $item_id SELECT rel_id FROM table2 WHERE rel_id = '$item_id' AND field_id = '42'" put that in $user_id But from reading examples on joins and inner joins I think there's a more elegant way. I cant wrap my brain around writing a better query (but would like to) I can describe how it should go: table1 fields: id, url table2 fields item_id, rel_id, field_id I know the last part of table1.url (LIKE '%/$filename') with that I select table1.id. table1.id is equal to one entry in table2.rel_id. So get that and select the table2.item_id. In table2 there is another entry which has the same table2.item_id and it will have a table2.field_id = '42' And finally the value I need is the table2.rel_id where the table2.field_id was 42. I will fetch that value and put it in $user_id Can this be done with one query using joins/inner joins?

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  • mysql_real_escape_string() just makes an empty string?

    - by James P
    I am using a jQuery AJAX request to a page called like.php that connects to my database and inserts a row. This is the like.php code: <?php // Some config stuff define(DB_HOST, 'localhost'); define(DB_USER, 'root'); define(DB_PASS, ''); define(DB_NAME, 'quicklike'); $link = mysql_connect(DB_HOST, DB_USER, DB_PASS) or die('ERROR: ' . mysql_error()); $sel = mysql_select_db(DB_NAME, $link) or die('ERROR: ' . mysql_error()); $likeMsg = mysql_real_escape_string(trim($_POST['likeMsg'])); $timeStamp = time(); if(empty($likeMsg)) die('ERROR: Message is empty'); $sql = "INSERT INTO `likes` (like_message, timestamp) VALUES ('$likeMsg', $timeStamp)"; $result = mysql_query($sql, $link) or die('ERROR: ' . mysql_error()); echo mysql_insert_id(); mysql_close($link); ?> The problematic line is $likeMsg = mysql_real_escape_string(trim($_POST['likeMsg']));. It seems to just return an empty string, and in my database under the like_message column all I see is blank entries. If I remove mysql_real_escape_string() though, it works fine. Here's my jQuery code if it helps. $('#like').bind('keydown', function(e) { if(e.keyCode == 13) { var likeMessage = $('#changer p').html(); if(likeMessage) { $.ajax({ cache: false, url: 'like.php', type: 'POST', data: { likeMsg: likeMessage }, success: function(data) { $('#like').unbind(); writeLikeButton(data); } }); } else { $('#button_container').html(''); } } }); All this jQuery code works fine, I've tested it myself independently. Any help is greatly appreciated, thanks.

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  • PHP + MySQL - Match first letter of directory

    - by user1822825
    Let's say I have a class table. In the class table, there are many students with their pictures. In the first registration, I've registered the class and students with pictures. The pictures were put into a directory like classid_classname. Then, I change the class name. Now, I'm adding the student's picture. Now, the new picture can't be recognized because the class name has changed. The pic url will be set as classid_class(new)name. How can I match the first letter of the directory? This is my update code : $classID= $_POST["classID"]; $className= $_POST["className"]; $p1 = $_FILES['p1']['name']; $p2 = $_FILES['p2']['name']; $p3 = $_FILES['p3']['name']; $direct = $_POST["className"]; $direct = strtolower($direct); $direct = str_replace(' ', '_', $direct); $tfish = $classID."_".$direct; //the directory variable will have new name because it can't be fetched if the directory has been changed many times// $file = "slider_imagesClass/".$tfish."/"; $url = "/".$tfish."/"; How can I make the variable to match the first letter of the directory because the classID will not change? Thank you. Really appreciate your help :D

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  • Commercial web application--scalable database design

    - by Rob Campbell
    I'm designing a set of web apps to track scientific laboratory data. Each laboratory has several members, each of whom will access both their own data and that of their laboratory as a whole. Many typical queries will thus be expected to return records of multiple members (e.g. my mouse, joe's mouse and sally's mouse). I think I have the database fairly well normalized. I'm now wondering how to ensure that users can efficiently access both their own data and their lab's data set when it is mixed among (hopefully) a whole ton of records from other labs. What I've come up with so far is that most tables will end with two fields: user_id and labgroup_id. The WHERE clause of any SELECT statement will include the appropriate reference to one of the id fields ("...WHERE 'labroup_id=n..." or "...WHERE user_id=n..."). My questions are: Is this an approach that will scale to 10^6 or more records? If so, what's the best way to use these fields in a query so that it most efficiently searches the relevant subset of the database? e.g. Should the first step in querying be to create a temporary table containing just the labgroup's data? Or will indexing using some combination of the id, user_id, and labroup_id fields be sufficient at that scale? I thank any responders very much in advance.

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  • Create a nested list

    - by sico87
    How would I create a nested list, I currently have this public function getNav($cat,$subcat){ //gets all sub categories for a specific category if(!$this->checkValue($cat)) return false; //checks data $query = false; if($cat=='NULL'){ $sql = "SELECT itemID, title, parent, url, description, image FROM p_cat WHERE deleted = 0 AND parent is NULL ORDER BY position;"; $query = $this->db->query($sql) or die($this->db->error); }else{ //die($cat); $sql = "SET @parent = (SELECT c.itemID FROM p_cat c WHERE url = '".$this->sql($cat)."' AND deleted = 0); SELECT c1.itemID, c1.title, c1.parent, c1.url, c1.description, c1.image, (SELECT c2.url FROM p_cat c2 WHERE c2.itemID = c1.parent LIMIT 1) as parentUrl FROM p_cat c1 WHERE c1.deleted = 0 AND c1.parent = @parent ORDER BY c1.position;"; $query = $this->db->multi_query($sql) or die($this->db->error); $this->db->store_result(); $this->db->next_result(); $query = $this->db->store_result(); } return $query; } public function getNav($cat=false, $subcat=false){ //gets a list of all categories form this level, if $cat is false it returns top level nav if($cat==false || strtolower($cat)=='all-products') $cat='NULL'; $ds = $this->data->getNav($cat, $subcat); $nav = $ds ? $ds : false; $html = ''; //create html if($nav){ $html = '<ul>'; //var_dump($nav->fetch_assoc()); while($row = $nav->fetch_assoc()){ $url = isset($row['parentUrl']) ? $row['parentUrl'].'/'.$row['url'] : $row['url']; $current = $subcat==$row['url'] ? ' class="current"' : ''; $html .= '<li'.$current.'><a href="/'.$url.'/">'.$row['title'].'</a></li>'; } $html .='</ul>'; } return $html; } The sql returns parents and children, for each parent I need the child to nest in a list.

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  • How to select parent row only if has at least one child?

    - by Matt McCormick
    I have a simple one-to-many relationship. I would like to select rows from the parent only when they have at least one child. So, if there are no children, then the parent row is not returned in the result set. Eg. Parent: +--+---------+ |id| text | +--+---------+ | 1| Blah | | 2| Blah2 | | 3| Blah3 | +--+---------+ Children +--+------+-------+ |id|parent| other | +--+------+-------+ | 1| 1 | blah | | 2| 1 | blah2 | | 3| 2 | blah3 | +--+------+-------+ I want the results to be: +----+------+ |p.id|p.text| +----+------+ | 1 | Blah | | 2 | Blah2| +----+------+

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  • How to use Insert .. select, with conditional vars from insert

    - by WmasterJ
    I have two separate tables both with user id columns uid. I want to take a value from all users in one table and insert it into the correct row for the correct user in the other table. INSERT INTO users2 (picture) SELECT pv.value FROM profile_values as pv, users2 as u WHERE pv.uid = u.uid AND pv.fid = 31 AND users2.uid=u.uid; But it's not working because i seem not to have access to users2.uid inside of the select statement. How would I accomplish this?

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  • How Can i Create This Complicated Query ?

    - by mTuran
    Hi, I have 3 tables: projects, skills and project_skills. In projects table i hold project's general data. Second table skills i hold skill id and skill name also i have projects_skills table which is hold project's skill relationships. Here is scheme of tables: CREATE TABLE IF NOT EXISTS `project_skills` ( `project_id` int(11) NOT NULL, `skill_id` int(11) NOT NULL, KEY `project_id` (`project_id`), KEY `skill_id` (`skill_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci; CREATE TABLE IF NOT EXISTS `projects` ( `id` int(11) NOT NULL AUTO_INCREMENT, `employer_id` int(11) NOT NULL, `project_title` varchar(100) COLLATE utf8_turkish_ci NOT NULL, `project_description` text COLLATE utf8_turkish_ci NOT NULL, `project_budget` int(11) NOT NULL, `project_allowedtime` int(11) NOT NULL, `project_deadline` datetime NOT NULL, `total_bids` int(11) NOT NULL, `average_bid` int(11) NOT NULL, `created` datetime NOT NULL, `active` tinyint(1) NOT NULL, PRIMARY KEY (`id`), KEY `created` (`created`), KEY `employer_id` (`employer_id`), KEY `active` (`active`), FULLTEXT KEY `project_title` (`project_title`,`project_description`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci AUTO_INCREMENT=3 ; CREATE TABLE IF NOT EXISTS `skills` ( `id` int(11) NOT NULL AUTO_INCREMENT, `category` int(11) NOT NULL, `name` varchar(100) COLLATE utf8_turkish_ci NOT NULL, `seo_name` varchar(100) COLLATE utf8_turkish_ci NOT NULL, `total_projects` int(11) NOT NULL, PRIMARY KEY (`id`), KEY `seo_name` (`seo_name`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci AUTO_INCREMENT=224 ; I want to select projects with related skill names. I think i have to use JOIN but i don't know how can i do. Thanks

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  • PHP While Loops from Arrays

    - by Michael
    I have a table that contains members names and a field with multiple ID numbers. I want to create a query that returns results where any values in the ID fields overlap with any values in the array. For example: lastname: Smith firstname: John id: 101, 103 I have Array #1 with the values 101, 102, 103 I want the query to output all members who have the values 101 or 102 or 103 listed in their id field with multiple ids listed. Array ( [0] => 101 [1] => 102 [2] => 103 ) $sql="SELECT firstname, lastname, id FROM members WHERE id LIKE '%".$array_num_1."%'"; $result=mysql_query($sql); while ($rows=mysql_fetch_array($result)) { echo $rows['lastname'].', '.$rows['firstname'].'-'.$rows['id']; }

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  • Broken Package on Update Manager

    - by Widy Graycloud
    I dont know what's wrong with my update manager.. It says that the softwares that I installed was broken. Maybe because I force shutdown my laptop, because Ubuntu wont shutdown,showing up desktop wallpaper but not title bar and launcher, but It won't shut down (+that's another bug). I've just update the broken softwares. the size is 60 to 70 MB.. But It doesn't work. Now I cannot update or install any software from Update Manager or Ubuntu Software Center. Can anybody tellme what's wrong? This is what appears when I use Update Manager I use Ubuntu Software Center, and this message appeared I chose repair and when it update the broken softwares using Ubuntu Software Center. It failed. And show up this message. The problem is I can't update or install any program from Ubuntu Software Center and Device Manager anymore. (I closed allprograms include ubuntu software center,and device manager in this case). Some one helpme? I tried to use apt-get install -f in terminal but it shows message like this: E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?

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  • MySQL Need some help with a query

    - by Jules
    I'm trying to fix some data by adding a new field. I have a backup from a few months ago and I have restored this database to my server. I'm looking at table called pads, its primary key is PadID and the field of importance is called RemoveMeDate. In my restored (older) database there is less records with an actual date set in RemoveMeDate. My control date is 2001-01-01 00:00:00 meaning that the record is not hidden aka visible. What I need to do is select all the records from the older database / table with the control date and join with those from the newer db /table where the control date is not set. I hope I've explained that correctly. I'll try again, with numbers. I have 80,000 visible records in the older table (with control date set) and 30,000 in the newer db/table. I need to select the 50,000 from the old database, to perform an update query. Heres my query, which I'd can't get to work as I'd like. jules-fix-reasons is the old database, jules is the newer one. select p.padid from `jules-fix-reasons`.`pads` p JOIN `jules`.`pads` ON p.padid = `jules`.`pads`.`PadID` where p.RemoveMeDate <> '2001-01-01 00:00:00' AND `jules`.`pads`.RemoveMeDate = '2001-01-01 00:00:00'

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  • MySQL error problem

    - by comma
    I keep getting the error listed below but it only says line 1 what does this mean and how do I fix it? Here is the error I keep getting? You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '1' at line 1 here is the code. if (isset($_POST['info_submitted'])) { $user_id = '5'; $mysqli = mysqli_connect("localhost", "root", "", "sitename"); $dbc = mysqli_query($mysqli,"SELECT learned_skills.*, users_skills.* FROM learned_skills INNER JOIN users_skills ON learned_skills.id = users_skills.skill_id WHERE user_id='$user_id'"); $skill = $_POST['skill']; $experience = $_POST['experience']; $year = $_POST['year']; if (mysqli_num_rows($dbc) == 0) { $mysqli = mysqli_connect("localhost", "root", "", "sitename"); $query1 = mysqli_query($mysqli,"INSERT INTO learned_skills (skill, experience, year) VALUES ('" . $skill . "', '" . $experience . "', '" . $year . "')"); } if (!mysqli_query($mysqli, $query1)) { print mysqli_error($mysqli); return; } $mysqli = mysqli_connect("localhost", "root", "", "sitename"); $dbc = mysqli_query($mysqli,"SELECT id FROM learned_skills WHERE id='" . $skill . "' AND experience='" . $experience . "' AND year='" . $year . "'"); if (!$dbc) { print mysqli_error($mysqli); } else { while($row = mysqli_fetch_array($dbc)){ $id = $row["id"]; } } $query2 = "INSERT INTO users_skills (skill_id, user_id, date_created) VALUES ('$id', '$user_id', NOW())"; if (!mysqli_query($mysqli, $query2)) { print mysqli_error($mysqli); return; } if ($dbc == TRUE) { $dbc = mysqli_query($mysqli,"UPDATE learned_skills JOIN users_skills ON (users_skills.skill_id = learned_skills.id) SET skill = '$skill', experience = '$experience', year = '$year'"); echo '<p class="changes-saved">Your changes have been saved!</p>'; } if (!$dbc) { print mysqli_error($mysqli); return; } }

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  • How to get count of another table in a left join

    - by Sinan
    I have multiple tables post id Name 1 post-name1 2 post-name2 user id username 1 user1 2 user2 post_user post_id user_id 1 1 2 1 post_comments post_id comment_id 1 1 1 2 1 3 I am using a query like this: SELECT post.id, post.title, user.id AS uid, username FROM `post` LEFT JOIN post_user ON post.id = post_user.post_id LEFT JOIN user ON user.id = post_user.user_id ORDER BY post_date DESC It works as intended. However I would like the get the number of comments for each post too. So how can i modify the this query so I can get the count of comments. Any ideas?

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  • mysqli real_escape_string problem

    - by tridat
    When im inserting to the database on my dev server the text goes in fine, for example "that's" is "that's" in the db. when uploading the exact same code to production server (hosted on a reseller account at bluehost) "that's" becomes "that\'s", im not double escaping, its exactly the same code, what could be the issue here?

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  • mysqli returns only one row instead of multiple rows

    - by Tristan
    Hello, i'm totally new to mysqli and i took a generated code and adapted it for my need. public function getServeurByName($string) { $stmt = mysqli_prepare($this->connection, "SELECT DISTINCT * FROM $this->tablename where GSP_nom=?"); $this->throwExceptionOnError(); mysqli_stmt_bind_param($stmt, 's', $string); $this->throwExceptionOnError(); mysqli_stmt_execute($stmt); $this->throwExceptionOnError(); mysqli_stmt_bind_result($stmt, $row->idServ, $row->timestamp, ........... ........... $row->email); if(mysqli_stmt_fetch($stmt)) { $row->timestamp = new DateTime($row->timestamp); return $row; } else { return null; } } the problem, this example i took the template on returns only one row instead of all the records. how to fix that please ?

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  • Invalid SQL Query

    - by svovaf
    I have the next query that in my opinion is a valid one, but I keep getting error telling me that there is a proble on "WHERE em.p4 = ue.p3" - Unknown column 'ue.p3' in 'where clause'. This is the query: SELECT DISTINCT ue.p3 FROM table1 AS ue INNER JOIN table2 AS e ON ue.p3 = e.p3 WHERE EXISTS( SELECT 1 FROM ( SELECT (COUNT(*) >= 1) AS MinMutual FROM table4 AS smm WHERE smm.p1 IN ( SELECT sem.p3 FROM table3 AS sem INNER JOIN table2 AS em ON sem.p3 = em.p3 WHERE em.p4 = ue.p3 AND sem.type = 'friends' AND em.p2 = 'normal' ) AND smm.p5 IN ( 15000,15151 ) ) AS Mutual WHERE Mutual.MinMutual = TRUE) LIMIT 11 If I execute the sub-query which is inside the EXISTS function, everything is O.K. PLEASE HELP!

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  • GROUP BY ID range?

    - by d0ugal
    Given a data set like this; +-----+---------------------+--------+ | id | date | result | +-----+---------------------+--------+ | 121 | 2009-07-11 13:23:24 | -1 | | 122 | 2009-07-11 13:23:24 | -1 | | 123 | 2009-07-11 13:23:24 | -1 | | 124 | 2009-07-11 13:23:24 | -1 | | 125 | 2009-07-11 13:23:24 | -1 | | 126 | 2009-07-11 13:23:24 | -1 | | 127 | 2009-07-11 13:23:24 | -1 | | 128 | 2009-07-11 13:23:24 | -1 | | 129 | 2009-07-11 13:23:24 | -1 | | 130 | 2009-07-11 13:23:24 | -1 | | 131 | 2009-07-11 13:23:24 | -1 | | 132 | 2009-07-11 13:23:24 | -1 | | 133 | 2009-07-11 13:23:24 | -1 | | 134 | 2009-07-11 13:23:24 | -1 | | 135 | 2009-07-11 13:23:24 | -1 | | 136 | 2009-07-11 13:23:24 | -1 | | 137 | 2009-07-11 13:23:24 | -1 | | 138 | 2009-07-11 13:23:24 | 1 | | 139 | 2009-07-11 13:23:24 | 0 | | 140 | 2009-07-11 13:23:24 | -1 | +-----+---------------------+--------+ How would I go about grouping the results by day 5 records at a time. The above results is part of the live data, there is over 100,000 results rows in the table and its growing. Basically I want to measure the change over time, so want to take a SUM of the result every X records. In the real data I'll be doing it ever 100 or 1000 but for the data above perhaps every 5. If i could sort it by date I would do something like this; SELECT DATE_FORMAT(date, '%h%i') ym, COUNT(result) 'Total Games', SUM(result) as 'Score' FROM nn_log GROUP BY ym; I can't figure out a way of doing something similar with numbers. The order is sorted by the date but I hope to split the data up every x results. It's safe to assume there are no blank rows. Doing it above with the data you could do multiple selects like; SELECT SUM(result) FROM table LIMIT 0,5; SELECT SUM(result) FROM table LIMIT 5,5; SELECT SUM(result) FROM table LIMIT 10,5; Thats obviously not a very good way to scale up to a bigger problem. I could just write a loop but I'd like to reduce the number of queries.

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  • Killing Mysql processes staying in sleep command.

    - by Shino88
    Hey I am connecting a MYSQL database through hibernate and i seem to have processes that are not being killed after they are finished in the session. I have called flush and close on each session but when i check the server the last processes are still there with a sleep command. This is a new problem which i am having and was not the case yesterday. Is there any way i can ensure the killng of theses processes when i am done with a session. Below is an example of one of my classes. public JSONObject check() { //creates a new session needed to add elements to a database Session session = null; //holds the result of the check in the database JSONObject check = new JSONObject(); try{ //creates a new session needed to add elements to a database SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); session = sessionFactory.openSession(); if (justusername){ //query created to select a username from user table String hquery = "Select username from User user Where username = ? "; //query created Query query = session.createQuery(hquery); //sets the username of the query the values JSONObject contents query.setString(0, username); // executes query and adds username string variable String user = (String) query.uniqueResult(); //checks to see if result is found (null if not found) if (user == null) { //adds false to Jobject if not found check.put("indatabase", "false"); } else { check.put("indatabase", "true"); } //adds check to Jobject to say just to check username check.put("justusername", true); } else { //query created to select a username and password from user table String hquery = "Select username from User user Where username = :user and password = :pass "; Query query = session.createQuery(hquery); query.setString("user", username); query.setString("pass", password); String user = (String) query.uniqueResult(); if(user ==null) { check.put("indatabase", false); } else { check.put("indatabase", true); } check.put("justusername", false); } }catch(Exception e){ System.out.println(e.getMessage()); //logg.log(Level.WARNING, " Exception", e.getMessage()); }finally{ // Actual contact insertion will happen at this step session.flush(); session.close(); } //returns Jobject return check; }

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  • MySQL - Calculating fields on the fly vs storing calculated data

    - by Christian Varga
    Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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  • MySQL LEFT OUTER JOIN virtual table

    - by user1707323
    I am working on a pretty complicated query let me try to explain it to you. Here is the tables that I have in my MySQL database: students Table --- `students` --- student_id first_name last_name current_status status_change_date ------------ ------------ ----------- ---------------- -------------------- 1 John Doe Active NULL 2 Jane Doe Retread 2012-02-01 students_have_courses Table --- `students_have_courses` --- students_student_id courses_course_id s_date e_date int_date --------------------- ------------------- ---------- ---------- ----------- 1 1 2012-01-01 2012-01-04 2012-01-05 1 2 2012-01-05 NULL NULL 2 1 2012-01-10 2012-01-11 NULL students_have_optional_courses Table --- `students_have_optional_courses` --- students_student_id optional_courses_opcourse_id s_date e_date --------------------- ------------------------------ ---------- ---------- 1 1 2012-01-02 2012-01-03 1 1 2012-01-06 NULL 1 5 2012-01-07 NULL Here is my query so far SELECT `students_and_courses`.student_id, `students_and_courses`.first_name, `students_and_courses`.last_name, `students_and_courses`.courses_course_id, `students_and_courses`.s_date, `students_and_courses`.e_date, `students_and_courses`.int_date, `students_have_optional_courses`.optional_courses_opcourse_id, `students_have_optional_courses`.s_date, `students_have_optional_courses`.e_date FROM ( SELECT `c_s_a_s`.student_id, `c_s_a_s`.first_name, `c_s_a_s`.last_name, `c_s_a_s`.courses_course_id, `c_s_a_s`.s_date, `c_s_a_s`.e_date, `c_s_a_s`.int_date FROM ( SELECT `students`.student_id, `students`.first_name, `students`.last_name, `students_have_courses`.courses_course_id, `students_have_courses`.s_date, `students_have_courses`.e_date, `students_have_courses`.int_date FROM `students` LEFT OUTER JOIN `students_have_courses` ON ( `students_have_courses`.`students_student_id` = `students`.`student_id` AND (( `students_have_courses`.`s_date` >= `students`.`status_change_date` AND `students`.current_status = 'Retread' ) OR `students`.current_status = 'Active') ) WHERE `students`.current_status = 'Active' OR `students`.current_status = 'Retread' ) `c_s_a_s` ORDER BY `c_s_a_s`.`courses_course_id` DESC ) `students_and_courses` LEFT OUTER JOIN `students_have_optional_courses` ON ( `students_have_optional_courses`.students_student_id = `students_and_courses`.student_id AND `students_have_optional_courses`.s_date >= `students_and_courses`.s_date AND `students_have_optional_courses`.e_date IS NULL ) GROUP BY `students_and_courses`.student_id; What I want to be returned is the student_id, first_name, and last_name for all Active or Retread students and then LEFT JOIN the highest course_id, s_date, e_date, and int_date for the those students where the s_date is since the status_change_date if status is 'Retread'. Then LEFT JOIN the highest optional_courses_opcourse_id, s_date, and e_date from the students_have_optional_courses TABLE where the students_have_optional_courses.s_date is greater or equal to the students_have_courses.s_date and the students_have_optional_courses.e_date IS NULL Here is what is being returned: student_id first_name last_name courses_course_id s_date e_date int_date optional_courses_opcourse_id s_date_1 e_date_1 ------------ ------------ ----------- ------------------- ---------- ---------- ------------ ------------------------------ ---------- ---------- 1 John Doe 2 2012-01-05 NULL NULL 1 2012-01-06 NULL 2 Jane Doe NULL NULL NULL NULL NULL NULL NULL Here is what I want being returned: student_id first_name last_name courses_course_id s_date e_date int_date optional_courses_opcourse_id s_date_1 e_date_1 ------------ ------------ ----------- ------------------- ---------- ---------- ------------ ------------------------------ ---------- ---------- 1 John Doe 2 2012-01-05 NULL NULL 5 2012-01-07 NULL 2 Jane Doe NULL NULL NULL NULL NULL NULL NULL Everything is working except one thing, I cannot seem to get the highest students_have_optional_courses.optional_courses_opcourse_id no matter how I form the query Sorry, I just solved this myself after writing this all out I think it helped me think of the solution. Here is the solution query: SELECT `students_and_courses`.student_id, `students_and_courses`.first_name, `students_and_courses`.last_name, `students_and_courses`.courses_course_id, `students_and_courses`.s_date, `students_and_courses`.e_date, `students_and_courses`.int_date, `students_optional_courses`.optional_courses_opcourse_id, `students_optional_courses`.s_date, `students_optional_courses`.e_date FROM ( SELECT `c_s_a_s`.student_id, `c_s_a_s`.first_name, `c_s_a_s`.last_name, `c_s_a_s`.courses_course_id, `c_s_a_s`.s_date, `c_s_a_s`.e_date, `c_s_a_s`.int_date FROM ( SELECT `students`.student_id, `students`.first_name, `students`.last_name, `students_have_courses`.courses_course_id, `students_have_courses`.s_date, `students_have_courses`.e_date, `students_have_courses`.int_date FROM `students` LEFT OUTER JOIN `students_have_courses` ON ( `students_have_courses`.`students_student_id` = `students`.`student_id` AND (( `students_have_courses`.`s_date` >= `students`.`status_change_date` AND `students`.current_status = 'Retread' ) OR `students`.current_status = 'Active') ) WHERE `students`.current_status = 'Active' OR `students`.current_status = 'Retread' ) `c_s_a_s` ORDER BY `c_s_a_s`.`courses_course_id` DESC ) `students_and_courses` LEFT OUTER JOIN ( SELECT * FROM `students_have_optional_courses` ORDER BY `students_have_optional_courses`.optional_courses_opcourse_id DESC ) `students_optional_courses` ON ( `students_optional_courses`.students_student_id = `students_and_courses`.student_id AND `students_optional_courses`.s_date >= `students_and_courses`.s_date AND `students_optional_courses`.e_date IS NULL ) GROUP BY `students_and_courses`.student_id;

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