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  • mysql query optimization

    - by vamsivanka
    I would need some help on how to optimize the query. select * from transaction where id < 7500001 order by id desc limit 16 when i do an explain plan on this - the type is "range" and rows is "7500000" According to the some online reference's this is explained as, it took the query 7,500,000 rows to scan and get the data. Is there any way i can optimize so it uses less rows to scan and get the data. Also, id is the primary key column.

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  • group by query issue

    - by user319088
    gorup by query issue i have one table, which has three fields and data. Name , Top , total cat , 1 ,10 dog , 2, 7 cat , 3 ,20 hourse 4, 4 cat, 5,10 Dog 6 9 i want to select record which has highest value of "total" for each Name so my result should be like this. Name , Top , total cat , 3 , 20 hourse , 4 , 4 Dog , 6 , 9 i tried group by name order by total, but it give top most record of group by result. any one can guide me , please!!!!

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  • What am I encrypting wrong here?

    - by Katie Krueger
    So I have a wordplay project to do and I have to encrypt some characters. I am at the point where I am stuck, and when I run it and type 1 for encrypt it doesn't shift that many letters. It just prints the work over again. I am wondering what I could do to fix it where if I say "hello" it will print 1 character over and say "ifmmp" Thank you! import java.util.Scanner; public class WordPlayTester{ public static void main(String [] args){ String word, reverse=""; String original; int key= 0; String Menu= "1-Encrypt \n2-Decrypt \n3-Is Palindrome \n0-Quit \n-Select an option-"; Scanner in = new Scanner(System.in); System.out.println("-Type any word-"); word = in.nextLine(); System.out.println(Menu); int choice=in.nextInt(); if(choice==1) { System.out.println("Insert a Key number"); int select= in.nextInt(); for (int i=0; i < word.length(); i++) { char c = word.charAt(i); if (c >= 'A' && c <= 'Z') { c = (char)(c - 64); int n = c+1; n = n % 26; if (n < 0) { n = n + 26; } c = (char)(n + 65); } System.out.println(c); } } else if(choice==3) { int length = word.length(); for ( int i = length - 1 ; i >= 0 ; i-- ) reverse = reverse + word.charAt(i); if (word.equals(reverse)) System.out.println("Your word is a palindrome."); else System.out.println("Your word is not a palindrome."); } else if(choice==0) { System.exit(0); } else { System.out.println(Menu); } } }

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  • MVC + Nhibernate + Oracle Schema Configuration

    - by Orkun Balkanci
    Our customer wants us to use a connectionstring with username = "external" and add schemaName "original" infront of our queries like: "select columnA from original.TableA" I dont want to change mapping files which are shared by other projects, tried adding default schema as: <property name="default_schema">original</property> But this doesn't work. Any Help?

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  • How can I use Generics to create a way of making an IEnumerable from an enum?

    - by Samantha J
    Given an enum like this: public enum City { London = 1, Liverpool = 20, Leeds = 25 } public enum House { OneFloor = 1, TwoFloors = 2 } I am using the following code to give me an IEnumerable: City[] values = (City[])Enum.GetValues(typeof(City)); var valuesWithNames = from value in values select new { value = (int)value, name = value.ToString() }; The code works very good however I have to do this for quite a lot of enums. Is there a way I could create a generic way of doing this?

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  • Is it possible to keep mysql migration running without keeping connection open?

    - by taw
    ALTER TABLE can easily take a few days - and during this time there's a non-negligible chance of connection getting terminated due to network problems. Is it possible to start ALTER TABLE (or CREATE TABLE ... SELECT ...; or some other very long running query) and leave it running without keeping connection open all the time? (the obvious solution of screen + console mysql client won't easily work as there's no ssh running on that server, only mysqld).

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  • SQL CASE WHEN NULL - question

    - by cc0
    Ok, so I'm trying to select an amount of rows from a column that holds the value 3, but only if there are no rows containing 10 or 4, if there are rows containing 10 or 4 I only want to show those. What would be a good syntax to do that? So far I've been attempting a CASE WHEN statement, but I can't seem to figure it out. Any help would be greatly appreciated. (My database is in an MS SQL 2008 server)

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  • MySQL replication - Should I handle load balancing from my client code (PHP) ?

    - by pirostraktor
    In a MySQL master-slave replication enviroment if I have 4 slave servers how can I execute load balanced select queries? Should I write a PHP class to dealing with the 4 slaves or it is possible to address queries to MySQL's own load balancer solution? Is there a MySQL load balancing solutions? Can I use some other tool to distribute my queries? What is the typical set up in situations like this? Thanks for all answers!

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  • How to convert this procedural programming to object-oriented programming?

    - by manus91
    I have a source code that is needed to be converted by creating classes, objects and methods. So far, I've just done by converting the initial main into a separate class. But I don't know what to do with constructor and which variables are supposed to be private. This is the code : import java.util.*; public class Card{ private static void shuffle(int[][] cards){ List<Integer> randoms = new ArrayList<Integer>(); Random randomizer = new Random(); for(int i = 0; i < 8;) { int r = randomizer.nextInt(8)+1; if(!randoms.contains(r)) { randoms.add(r); i++; } } List<Integer> clonedList = new ArrayList<Integer>(); clonedList.addAll(randoms); Collections.shuffle(clonedList); randoms.addAll(clonedList); Collections.shuffle(randoms); int i=0; for(int r=0; r < 4; r++){ for(int c=0; c < 4; c++){ cards[r][c] = randoms.get(i); i++; } } } public static void play() throws InterruptedException { int ans = 1; int preview; int r1,c1,r2,c2; int[][] cards = new int[4][4]; boolean[][] cardstatus = new boolean[4][4]; boolean gameover = false; int moves; Scanner input = new Scanner(System.in); do{ moves = 0; shuffle(cards); System.out.print("Enter the time(0 to 5) in seconds for the preview of the answer : "); preview = input.nextInt(); while((preview<0) || (preview>5)){ System.out.print("Invalid time!! Re-enter time(0 - 5) : "); preview = input.nextInt(); } preview = 1000*preview; System.out.println(" "); for (int i =0; i<4;i++){ for (int j=0;j<4;j++){ System.out.print(cards[i][j]); System.out.print(" "); } System.out.println(""); System.out.println(""); } Thread.sleep(preview); for(int b=0;b<25;b++){ System.out.println(" "); } for(int r=0;r<4;r++){ for(int c=0;c<4;c++){ System.out.print("*"); System.out.print(" "); cardstatus[r][c] = false; } System.out.println(""); System.out.println(" "); } System.out.println(""); do{ do{ System.out.print("Please insert the first card row : "); r1 = input.nextInt(); while((r1<1) || (r1>4)){ System.out.print("Invalid coordinate!! Re-enter first card row : "); r1 = input.nextInt(); } System.out.print("Please insert the first card column : "); c1 = input.nextInt(); while((c1<1) || (c1>4)){ System.out.print("Invalid coordinate!! Re-enter first card column : "); c1 = input.nextInt(); } if(cardstatus[r1-1][c1-1] == true){ System.out.println("The card is already flipped!! Select another card."); System.out.println(""); } }while(cardstatus[r1-1][c1-1] != false); do{ System.out.print("Please insert the second card row : "); r2 = input.nextInt(); while((r2<1) || (r2>4)){ System.out.print("Invalid coordinate!! Re-enter second card row : "); r2 = input.nextInt(); } System.out.print("Please insert the second card column : "); c2 = input.nextInt(); while((c2<1) || (c2>4)){ System.out.print("Invalid coordinate!! Re-enter second card column : "); c2 = input.nextInt(); } if(cardstatus[r2-1][c2-1] == true){ System.out.println("The card is already flipped!! Select another card."); } if((r1==r2)&&(c1==c2)){ System.out.println("You can't select the same card twice!!"); continue; } }while(cardstatus[r2-1][c2-1] != false); r1--; c1--; r2--; c2--; System.out.println(""); System.out.println(""); System.out.println(""); for(int r=0;r<4;r++){ for(int c=0;c<4;c++){ if((r==r1)&&(c==c1)){ System.out.print(cards[r][c]); System.out.print(" "); } else if((r==r2)&&(c==c2)){ System.out.print(cards[r][c]); System.out.print(" "); } else if(cardstatus[r][c] == true){ System.out.print(cards[r][c]); System.out.print(" "); } else{ System.out.print("*"); System.out.print(" "); } } System.out.println(" "); System.out.println(" "); } System.out.println(""); if(cards[r1][c1] == cards[r2][c2]){ System.out.println("Cards Matched!!"); cardstatus[r1][c1] = true; cardstatus[r2][c2] = true; } else{ System.out.println("No cards match!!"); } Thread.sleep(2000); for(int b=0;b<25;b++){ System.out.println(""); } for(int r=0;r<4;r++){ for(int c=0;c<4;c++){ if(cardstatus[r][c] == true){ System.out.print(cards[r][c]); System.out.print(" "); } else{ System.out.print("*"); System.out.print(" "); } } System.out.println(""); System.out.println(" "); } System.out.println(""); System.out.println(""); System.out.println(""); gameover = true; for(int r=0;r<4;r++){ for( int c=0;c<4;c++){ if(cardstatus[r][c]==false){ gameover = false; break; } } if(gameover==false){ break; } } moves++; }while(gameover != true); System.out.println("Congratulations, you won!!"); System.out.println("It required " + moves + " moves to finish it."); System.out.println(""); System.out.print("Would you like to play again? (1=Yes / 0=No) : "); ans = input.nextInt(); }while(ans == 1); } } The main class is: import java.util.*; public class PlayCard{ public static void main(String[] args) throws InterruptedException{ Card game = new Card(); game.play(); } } Should I simplify the Card class by creating other classes? Through this code, my javadoc has no constructtor. So i need help on this!

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  • Multiple OR Clauses in MySQL

    - by Grant
    I'm trying to grab content where id = 3 OR id = 9 OR id = 100... Keep in mind, I can have a few hundred of these ids. What is the most efficient way to write my query? $sql = "SELECT name FROM artists WHERE (id=3 OR id=9 OR .... id-100)"

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  • Deleting Multiple rows from a TableView

    - by Sid
    hi Frnz, i want to delete multiple rows from a table view based on users selection.obviously i cant use didSelectRowAtIndexPath method coz it will be called for every row selected. i want to allow user to select multiple rows for deletion and then delete them in one go...Is it possible if yes then how to go about it.Also i am using a single view based project and i want the header of table view changed to "Delete" on the same view when the user want to delete the rows from the view. Thx

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  • MySQL: fetching a null or an empty string

    - by Oden
    Hey, I know whats the difference between a NULL value and an empty string ("") value, but if I want to get a value by using the OR keyword, I get no result for a NULL value The table i want to query looks like this: titles_and_tags +----+----------+------+ | id | title | tag | +----+----------+------+ | 1 | title1 | NULL | | 2 | title2 | tag1 | | 3 | title3 | tag2 | +----+----------+------+ The query i use looks like this: select * from `titles_and_tags` WHERE `title` LIKE "title" AND `tag` = "tag1" OR `tag` IS NULL So i want to get here a rows (id: 1,2), BUT this results 0 rows. What have i done wrong?

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  • Why was this T-SQL Syntax never implemented?

    - by ChrisA
    Why did they never let us do this sort of thing: Create Proc RunParameterisedSelect @tableName varchar(100), @columnName varchar(100), @value varchar(100) as select * from @tableName where @columnName = @value You can use @value as a parameter, obviously, and you can achieve the whole thing with dynamic SQL, but creating it is invariably a pain. So why didn't they make it part of the language in some way, rather than forcing you to EXEC(@sql)?

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  • Filter list as a parameter in a compiled query

    - by JK
    I have the following compiled query that I want to return a list of "groups" that don't have a "GroupID" that's contained in a filtered list: CompiledQuery.Compile(ConfigEntities contexty, List list) = from c in context.Groups where (!csList.Contains(c.GroupID)) select c).ToList() However I'm getting the following run-time error: The specified parameter 'categories' of type 'System.Collections.Generic.List`1[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c261364e126]]' is not valid. Only scalar parameters (such as Int32, Decimal, and Guid) are supported. Any ideas?

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  • Java: Making concurrent MySQL queries from multiple clients synchronised

    - by Misha Gale
    I work at a gaming cybercafe, and we've got a system here (smartlaunch) which keeps track of game licenses. I've written a program which interfaces with this system (actually, with it's backend MySQL database). The program is meant to be run on a client PC and (1) query the database to select an unused license from the pool available, then (2) mark this license as in use by the client PC. The problem is, I've got a concurrency bug. The program is meant to be launched simultaneously on multiple machines, and when this happens, some machines often try and acquire the same license. I think that this is because steps (1) and (2) are not synchronised, i.e. one program determines that license #5 is available and selects it, but before it can mark #5 as in use another copy of the program on another PC tries to grab that same license. I've tried to solve this problem by using transactions and table locking, but it doesn't seem to make any difference - Am I doing this right? Here follows the code in question: public LicenseKey Acquire() throws SmartLaunchException, SQLException { Connection conn = SmartLaunchDB.getConnection(); int PCID = SmartLaunchDB.getCurrentPCID(); conn.createStatement().execute("LOCK TABLE `licensekeys` WRITE"); String sql = "SELECT * FROM `licensekeys` WHERE `InUseByPC` = 0 AND LicenseSetupID = ? ORDER BY `ID` DESC LIMIT 1"; PreparedStatement statement = conn.prepareStatement(sql); statement.setInt(1, this.id); ResultSet results = statement.executeQuery(); if (results.next()) { int licenseID = results.getInt("ID"); sql = "UPDATE `licensekeys` SET `InUseByPC` = ? WHERE `ID` = ?"; statement = conn.prepareStatement(sql); statement.setInt(1, PCID); statement.setInt(2, licenseID); statement.executeUpdate(); statement.close(); conn.commit(); conn.createStatement().execute("UNLOCK TABLES"); return new LicenseKey(results.getInt("ID"), this, results.getString("LicenseKey"), results.getInt("LicenseKeyType")); } else { throw new SmartLaunchException("All licenses of type " + this.name + "are in use"); } }

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