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  • is NATURAL JOIN any better than SELECT FROM WHERE in terms of performance ?

    - by ashy_32bit
    Today I got into a debate with my project manager about Cartesian products. He says a 'natural join' is somehow much better than using 'select from where' because the later cause the db engine to internally perform a Cartesian product but the former uses another approach that prevents this. As far as I know, the natural join syntax is not any different in anyway than 'select from where' in terms of performance or meaning, I mean you can use either based on your taste. SELECT * FROM table1,table2 WHERE table1.id=table2.id SELECT * FROM table1 NATURAL JOIN table2 please elaborate about the first query causing a Cartesian product but the second one being somehow more smart

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  • Adding Related Entities without using navigation properties

    - by Barisa Puter
    I have the following classes, set for testing: public class Company { [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public int Id { get; set; } public string Name { get; set; } } public class Employee { [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public int Id { get; set; } public string Name { get; set; } public int CompanyId { get; set; } public virtual Company Company { get; set; } } public class EFTestDbContext : DbContext { public DbSet<Employee> Employees { get; set; } public DbSet<Company> Companies { get; set; } } For the sake of testing, I wanted to insert one company and one employee for that company with single SaveChanges call, like this: Company company = new Company { Name = "Sample company" }; context.Companies.Add(company); // ** UNCOMMENTED FOR TEST 2 //Company company2 = new Company //{ // Name = "Some other company" //}; //context.Companies.Add(company2); Employee employee = new Employee { Name = "Hans", CompanyId = company.Id }; context.Employees.Add(employee); context.SaveChanges(); Even though I am not using navigational properties, but instead I've made relation over Id, this somehow mysteriously worked - employee was saved with proper foreign key to company which got updated from 0 to real value, which made me go ?!?! Some hidden C# feature? Then I've decided to add more code, which is commented in the snippet above, making it to be inserting of 2 x Company entity and 1 x Employee entity, and then I got exception: Unable to determine the principal end of the 'CodeLab.EFTest.Employee_Company' relationship. Multiple added entities may have the same primary key. Does this mean that in cases where foreign key is 0, and there is a single matching entity being inserted in same SaveChanges transaction, Entity Framework will assume that foreign key should be for that matching entity? In second test, when there are two entities matching the relation type, Entity Framework throws an exception as it is not able to figure out to which of the Companies Employee should be related to.

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  • Merging rows with uniqueness constraints

    - by Flambino
    I've got a little time-tracking web app (implemented in Rails 3.2.8 & MySQL). The app has several users who add their time to specific tasks, on a given date. The system is set up so a user can only have 1 time entry (i.e. row) per task per date. I.e. if you add time twice on the same task and date, it'll add time to the existing row, rather than create a new one. Now I'm looking to merge 2 tasks. In the simplest terms, merging task ID 2 into task ID 1 would take this time | user_id | task_id | date ------+----------+----------+----------- 10 | 1 | 1 | 2012-10-29 15 | 2 | 1 | 2012-10-29 10 | 1 | 2 | 2012-10-29 5 | 3 | 2 | 2012-10-29 and change it into this time | user_id | task_id | date ------+----------+----------+----------- 20 | 1 | 1 | 2012-10-29 <-- time values merged (summed) 15 | 2 | 1 | 2012-10-29 <-- no change 5 | 3 | 1 | 2012-10-29 <-- task_id changed (no merging necessary) I.e. merge by summing the time values, where the given user_id/date/task combo would conflict. I figure I can use a unique constraint to do a ON DUPLICATE KEY UPDATE ... if I do an insert for every task_id=2 entry. But that seems pretty inelegant. I've also tried to figure a way to first update all the rows in task 1 with the summed-up times, but I can't quite figure that one out. Any ideas?

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  • Help with sql query

    - by user225269
    I have two tables: subject and student. I'm trying to count the number of subjects enrolled by each student. How do I do that?I'm trying the code below but it doesn't give the answer I need. Please help. SELECT COUNT( subject.SUBJECT ) , student.IDNO, student.FIRSTNAME, subject.SUBJECT FROM student, subject GROUP BY subject.SUBJECT LIMIT 0 , 30

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  • get index name within specific table name

    - by AmRoSH
    I need to check if this index not exist in specific table name not in all tables because this select statement select all indexes under this condition. IF NOT EXISTS (SELECT name from sysindexes WHERE name = 'IDX_InsuranceID') CREATE NONCLUSTERED INDEX [IDX_InsuranceID] ON [dbo].[QuoteInsurances] ( [InsuranceID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY] GO Thanks,

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  • Getting rows which include a value with MySQL

    - by sundowatch
    I have a MySQL query which gets including some vars like that: messages TABLE receiver cols user1 rows : 1,3,5 user2 rows : 2,3 user3 rows : 1,4 I want to get rows which includes '3' value. So I will get 'user1' and 'user2'. I tried that but naturally it doesn't work. mysql_query("SELECT * FROM messages WHERE receiver='3'"); How can I do this?

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  • Determining child count of path

    - by sqlnewbie
    I have a table whose 'path' column has values and I would like to update the table's 'child_count' column so that I get the following output. path | child_count --------+------------- | 5 /a | 3 /a/a | 0 /a/b | 1 /a/b/c | 0 /b | 0 My present solution - which is way too inefficient - uses a stored procedure as follows: CREATE FUNCTION child_count() RETURNS VOID AS $$ DECLARE parent VARCHAR; BEGIN FOR parent IN SELECT path FROM my_table LOOP DECLARE tokens VARCHAR[] := REGEXP_SPLIT_TO_ARRAY(parent, '/'); str VARCHAR := ''; BEGIN FOR i IN 2..ARRAY_LENGTH(tokens, 1) LOOP UPDATE my_table SET child_count = child_count + 1 WHERE path = str; str := str || '/' || tokens[i]; END LOOP; END; END LOOP; END; $$ LANGUAGE plpgsql; Anyone knows of a single UPDATE statement that does the same thing?

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  • Fetch multiple rows from SQL in PHP foreach item in array

    - by TrySpace
    I try to request an array of IDs, to return each row with that ID, and push each into an Array $finalArray But only the first result from the Query will output, and at the second foreach, it skips the while loop. I have this working in another script, so I don't understand where it's going wrong. The $arrayItems is an array containing: "home, info" $finalArray = array(); foreach ($arrayItems as $UID_get) { $Query = "SELECT * FROM items WHERE (uid = '" . cleanQuery($UID_get) . "' ) ORDER BY uid"; if($Result = $mysqli->query($Query)) { print_r($UID_get); echo "<BR><-><BR>"; while ($Row = $Result->fetch_assoc()) { array_push($finalArray , $Row); print_r($finalArray ); echo "<BR><><BR>"; } } else { echo '{ "returned" : "FAIL" }'; //. mysqli_connect_errno() . ' ' . mysqli_connect_error() . "<BR>"; } } (the cleanQuery is to escape and stripslashes) What I'm trying to get is an array of multiple rows (after i json_encoded it, like: {"finalArray" : { "home": {"id":"1","created":"0000-00-00 00:00:00","css":"{ \"background-color\" : \"red\" }"} }, { "info": {"id":"2","created":"0000-00-00 00:00:00","css":"{ \"background-color\" : \"blue\" }"} } } But that's after I get both, or more results from the db. the print_r($UID_get); does print info, but then nothing.. So, why am I not getting the second row from info? I am essentially re-querying foreach $arrayItem right?

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  • Improve SQL query performance

    - by Anax
    I have three tables where I store actual person data (person), teams (team) and entries (athlete). The schema of the three tables is: In each team there might be two or more athletes. I'm trying to create a query to produce the most frequent pairs, meaning people who play in teams of two. I came up with the following query: SELECT p1.surname, p1.name, p2.surname, p2.name, COUNT(*) AS freq FROM person p1, athlete a1, person p2, athlete a2 WHERE p1.id = a1.person_id AND p2.id = a2.person_id AND a1.team_id = a2.team_id AND a1.team_id IN ( SELECT id FROM team, athlete WHERE team.id = athlete.team_id GROUP BY team.id HAVING COUNT(*) = 2 ) GROUP BY p1.id ORDER BY freq DESC Obviously this is a resource consuming query. Is there a way to improve it?

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  • difference between where and nested queries

    - by Chris H
    I'm not able to figure out the difference between these queries. I'm pretty sure that the first one is an equi-join. I'm not sure how the second one ISN'T the same as the first. The sub query in #2 selects all Ids from S, and then it returns all R's that also have those ID's, no? SELECT R.cname FROM R, S, WHERE R.Id = S.Id SELECT R.cname FROM R WHERE R.Id IN (SELECT S.Id FROM S)

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  • PHP is truncating MSSQL Blob data (4096b), even after setting INI values. Am I missing one?

    - by Dutchie432
    I am writing a PHP script that goes through a table and extracts the varbinary(max) blob data from each record into an external file. The code is working perfectly, except when a file is over 4096b - the data is truncated at exactly 4096. I've modified the values for mssql.textlimit, mssql.textsize, and odbc.defaultlrl without any success. Am I missing something here? <?php ini_set("mssql.textlimit" , "2147483647"); ini_set("mssql.textsize" , "2147483647"); ini_set("odbc.defaultlrl", "0"); include_once('common.php'); $id=$_REQUEST['i']; $q = odbc_exec($connect, "Select id,filename,documentBin from Projectdocuments where id = $id"); if (odbc_fetch_row($q)){ echo "Trying $filename ... "; $fileName="projectPhotos/docs/".odbc_result($q,"filename"); if (file_exists($fileName)){ unlink($fileName); } if($fh = fopen($fileName, "wb")) { $binData=odbc_result($q,"documentBin"); fwrite($fh, $binData) ; fclose($fh); $size = filesize($fileName); echo ("$fileName<br />Done ($size)<br><br>"); }else { echo ("$fileName Failed<br>"); } } ?> OUTPUT Trying ... projectPhotos/docs/file1.pdf Done (4096) Trying ... projectPhotos/docs/file2.zip Done (4096) Trying ... projectPhotos/docsv3.pdf Done (4096) etc..

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  • sql query is too slow, how to improve speed

    - by user1289282
    I have run into a bottleneck when trying to update one of my tables. The player table has, among other things, id, skill, school, weight. What I am trying to do is: SELECT id, skill FROM player WHERE player.school = (current school of 4500) AND player.weight = (current weight of 14) to find the highest skill of all players returned from the query UPDATE player SET starter = 'TRUE' WHERE id = (highest skill) move to next weight and repeat when all weights have been completed move to next school and start over all schools completed, done I have this code implemented and it works, but I have approximately 4500 schools totaling 172000 players and the way I have it now, it would take probably a half hour or more to complete (did not wait it out), which is way too slow. How to speed this up? Short of reducing the scale of the system, I am willing to do anything that gets the intended result. Thanks! *the weights are the standard folk style wrestling weights ie, 103, 113, 120, 126, 132, 138, 145, 152, 160, 170, 182, 195, 220, 285 pounds

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  • How to login users that are stored within a Wordpress account

    - by user3716795
    I am developing an iOS app that is password protected and all the users are stored in a wordpress account that, of course, is password protected as well. Does anybody know the format that wordpress uses to store login information for these accounts, I would assume that it is a MySQL that sends a json? I have only been able to find the database code for the initial admin page but nothing that shows the way these accounts (815 to be exact) would be stored within the site.

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  • sports league database design

    - by John
    Hello, I'm developing a database to store statistics for a sports league. I'd like to show several tables: - league table that indicates the position of the team in the current and previous fixture - table that shows the position of a team in every fixture in the championship I have a matches table: Matches (IdMatch, IdTeam1, IdTeam2, GoalsTeam1, GoalsTeam2) Whith this table I can calculate the total points of every team based on the matches the team played. But every time I want to show the league table I have to calculate the points. Also I have a problem to calculate in which position classified a team in the last 10 fixtures cause I have to make 10 queries. To store the league table for every fixture in a database table is another approach, but every time I change a match already played I have to recalculate every fixture from there... Is there a better approach for this problem? Thanks

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  • Export SQL Binary/BLOB Data?

    - by davemackey
    Recently a software application we utilize upgraded from ASP to ASP.NET. In the process they abandoned the old web-based product and rewrote the entire UI, using new DB tables. The old DB tables still exist in the database and contain legacy files in binary or blob formats. I'm wondering if there is an easy way to export all these legacy files from the database to the filesystem (NTFS)? Then we could delete these old unused tables and save a few GB of space in the DB backups, etc.

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  • Does the order of the columns in a SELECT statement make a difference?

    - by Frank Computer
    This question was inspired by a previous question posted on SO, "Does the order of the WHERE clause make a differnece?". Would it improve a SELECT statement's performance if the the columns used in the WHERE section are placed at the begining of the SELECT statement? example: SELECT customer.id, transaction.id, transaction.efective_date, transaction.a, [...] FROM customer, transaction WHERE customer.id = transaction.id; I do know that limiting the list of columns to only the needed ones in a SELECT statement improves performance as opposed to using SELECT * because the current list is smaller.

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  • Filter Phrase Query

    - by alsuelo
    I try to filter a phrase to make a search in my website i've this query, this code working with one word but when i type wit more than one isn't working becuase the print is without spaces. $phrase = $this->getState($this->context.".filter_phrase"); printf("Original string: %s\n", $phrase); if(!empty($phrase)) { $escaped = $db->escape($phrase, true); printf("Escaped string: %s\n", $escaped); $quoted = $db->quote("%" . $escaped . "%" , false); $query->where ('a.title LIKE ' .$quoted); } Example i type king and the output is king , when i type the king the output is theking, i want to know if exist any way to conserve the blank spaces.

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  • MySql Query to return number of photos in each album

    - by GivenPie
    MY table is set up like this, all I need to do is call a query to my Photos table. I have PhotoID as the primary key and GalleryID as the foreign key to Gallery. How can I could the number of unique PhotoID's for each multiple GalleryIDs. So to speak there are may duplicate GalleryIDs because there are many photos in a gallery. So I just need to could the number of unique PhotoIDs associated with that GalleryID. Can it be done in one query?

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  • Automatically Persisting a Complex Java Object

    - by VeeArr
    For a project I am working on, I need to persist a number of POJOs to a database. The POJOs class definitions are sometimes highly nested, but they should flatten okay, as the nesting is tree-like and contains no cycles (and the base elements are eventually primitives/Strings). It is preferred that the solution used create one table per data type and that the tables will have one field per primitive member in the POJO. Subclassing and similar problems are not issues for this particular project. Does anybody know of any existing solutions that can: Automatically generate a CREATE TABLE definition from the class definition Automatically generate a query to persist an object to the database, given an instance of the object Automatically generate a query to retrieve an object from the database and return it as a POJO, given a key. Solutions that can do this with minimum modifications/annotions to the class files and minimum external configuration are preferred. Example: Java classes //Class to be persisted class TypeA { String guid; long timestamp; TypeB data1; TypeC data2; } class TypeB { int id; int someData; } class TypeC { int id; int otherData; } Could map to CREATE TABLE TypeA ( guid CHAR(255), timestamp BIGINT, data1_id INT, data1_someData INT, data2_id INt, data2_otherData INT ); Or something similar.

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  • sDesigning a database with flexible user profile

    - by Mughrabi
    I am working on a design where I can have flexible attributes for users and I am confused how to continue the design of the schema. I made a table where I kept system needed information: Table name: users id username password Now, I wish to create a profile table and have one to one relation where all the other attributes in profile table such as email, first name, last name, etc. My question is: is there a way to add a third table in which profiles will be flexible? In other words, if my clients need to create a new attribute he/she won't need any customization to the code.

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  • How to count number of occurences for all different values in database column?

    - by drasto
    I have a Postgre database that has say 10 columns. The fifth column is called column5. There are 100 rows in the database and possible values of column5 are c5value1, c5value2, c5value3...c5value29, c5value30. I would like to print out a table that shows how many times each value occurs. So the table would look like this: Value(of column5) number of occurrences of the value c5value1 1 c5value2 5 c5value3 3 c5value4 9 c5value5 1 c5value6 1 . . . . . . What is the command that does that? Thanks for help

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