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  • Should experienced programmers know database queries?

    - by Shamim Hafiz
    There are so many programmers out there who are also an expert at Query writing and Database design. Should this be a core requirement to be an expert programmer or software engineer? Though there are lots of similarities in the way queries and codes are developed, my personal opinion is, Queries seem to have a different Structure than Code and it can be tough to Master both simultaneously due to the different approaches.

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  • Temporary Tables in Stored Procedures

    - by Paul White
    Ask anyone what the primary advantage of temporary tables over table variables is, and the chances are they will say that temporary tables support statistics and table variables do not. This is true, of course; even the indexes that enforce PRIMARY KEY and UNIQUE constraints on table variables do not have populated statistics associated with them, and it is not possible to manually create statistics or non-constraint indexes on table variables. Intuitively, then, any query that has alternative execution...(read more)

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  • SQL SERVER – Concurrancy Problems and their Relationship with Isolation Level

    - by pinaldave
    Concurrency is simply put capability of the machine to support two or more transactions working with the same data at the same time. This usually comes up with data is being modified, as during the retrieval of the data this is not the issue. Most of the concurrency problems can be avoided by SQL Locks. There are four types of concurrency problems visible in the normal programming. 1)      Lost Update – This problem occurs when there are two transactions involved and both are unaware of each other. The transaction which occurs later overwrites the transactions created by the earlier update. 2)      Dirty Reads – This problem occurs when a transactions selects data that isn’t committed by another transaction leading to read the data which may not exists when transactions are over. Example: Transaction 1 changes the row. Transaction 2 changes the row. Transaction 1 rolls back the changes. Transaction 2 has selected the row which does not exist. 3)      Nonrepeatable Reads – This problem occurs when two SELECT statements of the same data results in different values because another transactions has updated the data between the two SELECT statements. Example: Transaction 1 selects a row, which is later on updated by Transaction 2. When Transaction A later on selects the row it gets different value. 4)      Phantom Reads – This problem occurs when UPDATE/DELETE is happening on one set of data and INSERT/UPDATE is happening on the same set of data leading inconsistent data in earlier transaction when both the transactions are over. Example: Transaction 1 is deleting 10 rows which are marked as deleting rows, during the same time Transaction 2 inserts row marked as deleted. When Transaction 1 is done deleting rows, there will be still rows marked to be deleted. When two or more transactions are updating the data, concurrency is the biggest issue. I commonly see people toying around with isolation level or locking hints (e.g. NOLOCK) etc, which can very well compromise your data integrity leading to much larger issue in future. Here is the quick mapping of the isolation level with concurrency problems: Isolation Dirty Reads Lost Update Nonrepeatable Reads Phantom Reads Read Uncommitted Yes Yes Yes Yes Read Committed No Yes Yes Yes Repeatable Read No No No Yes Snapshot No No No No Serializable No No No No I hope this 400 word small article gives some quick understanding on concurrency issues and their relation to isolation level. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Use ROLL UP Clause instead of COMPUTE BY

    - by pinaldave
    Note: This upgrade was test performed on development server with using bits of SQL Server 2012 RC0 (which was available at in public) when this test was performed. However, SQL Server RTM (GA on April 1) is expected to behave similarly. I recently observed an upgrade from SQL Server 2005 to SQL Server 2012 with compatibility keeping at SQL Server 2012 (110). After upgrading the system and testing the various modules of the application, we quickly observed that few of the reports were not working. They were throwing error. When looked at carefully I noticed that it was using COMPUTE BY clause, which is deprecated in SQL Server 2012. COMPUTE BY clause is replaced by ROLL UP clause in SQL Server 2012. However there is no direct replacement of the code, user have to re-write quite a few things when using ROLL UP instead of COMPUTE BY. The primary reason is that how each of them returns results. In original code COMPUTE BY was resulting lots of result set but ROLL UP. Here is the example of the similar code of ROLL UP and COMPUTE BY. I personally find the ROLL UP much easier than COMPUTE BY as it returns all the results in single resultset unlike the other one. Here is the quick code which I wrote to demonstrate the said behavior. CREATE TABLE tblPopulation ( Country VARCHAR(100), [State] VARCHAR(100), City VARCHAR(100), [Population (in Millions)] INT ) GO INSERT INTO tblPopulation VALUES('India', 'Delhi','East Delhi',9 ) INSERT INTO tblPopulation VALUES('India', 'Delhi','South Delhi',8 ) INSERT INTO tblPopulation VALUES('India', 'Delhi','North Delhi',5.5) INSERT INTO tblPopulation VALUES('India', 'Delhi','West Delhi',7.5) INSERT INTO tblPopulation VALUES('India', 'Karnataka','Bangalore',9.5) INSERT INTO tblPopulation VALUES('India', 'Karnataka','Belur',2.5) INSERT INTO tblPopulation VALUES('India', 'Karnataka','Manipal',1.5) INSERT INTO tblPopulation VALUES('India', 'Maharastra','Mumbai',30) INSERT INTO tblPopulation VALUES('India', 'Maharastra','Pune',20) INSERT INTO tblPopulation VALUES('India', 'Maharastra','Nagpur',11 ) INSERT INTO tblPopulation VALUES('India', 'Maharastra','Nashik',6.5) GO SELECT Country,[State],City, SUM ([Population (in Millions)]) AS [Population (in Millions)] FROM tblPopulation GROUP BY Country,[State],City WITH ROLLUP GO SELECT Country,[State],City, [Population (in Millions)] FROM tblPopulation ORDER BY Country,[State],City COMPUTE SUM([Population (in Millions)]) BY Country,[State]--,City GO After writing this blog post I continuously feel that there should be some better way to do the same task. Is there any easier way to replace COMPUTE BY? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Oracle Index Skip Scan

    - by jchang
    There is a feature, called index skip scan that has been in Oracle since version 9i. When I across this, it seemed like a very clever trick, but not a critical capability. More recently, I have been advocating DW on SSD in approrpiate situations, and I am thinking this is now a valuable feature in keeping the number of nonclustered indexes to a minimum. Briefly, suppose we have an index with key columns: Col1 , Col2 , in that order. Obviously, a query with a search argument (SARG) on Col1 can use...(read more)

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  • creating a pre-menu level select screen

    - by Ephiras
    Hi I am working on creating a tower Defence java applet game and have come to a road block about implementing a title screen that i can select the level and difficulty of the rest of the game. my title screen class is called Menu. from this menu class i need to pass in many different variables into my Main class. i have used different classes before and know how to run them and such. but if both classes extend applet and each has its individual graphics method how can i run things from Main even though it was created in Menu. what i essentially want to do is run the Menu class withits action listeners and graphics until a Difficulty button has been selected, run the main class (which 100% works without having to have the Menu class) and pretty much terminate Menu so that i cannot go back to it, do not see its buttons or graphics menus. can i run one applet annd when i choose a button close that one and launch the other one? IF you would like to download the full project you can find it here, i had to comment out all the code that wasn't working my Menu class import java.awt.*; import java.awt.event.*; import java.applet.*; public class Menu extends Applet implements ActionListener{ Button bEasy,bMed,bHard; Main m; public void init(){ bEasy= new Button("Easy"); bEasy.setBounds(140,200,100,50); add(bEasy); bMed = new Button("Medium");bMed.setBounds(280,200,100,50); add(bMed); bHard= new Button("Hard");bHard.setBounds(420,200,100,50); add(bHard); setLayout(null); } public void actionPerformed(ActionEvent e){ Main m = new Main(20,10,3000,mapMed);//break; switch (e.getSource()){ case bEasy: Main m = new Main(6000,20,"levels/levelEasy.png");break;//enimies tower money world case bMed: Main m = new Main(4000,15,"levels/levelMed.png");break; case bHard: Main m = new Main(2000,10,"levels/levelEasy.png");break; default: break; } } public void paint(){ //m.draw(g) } } and here is my main class initialising code. import java.awt.*; import java.awt.event.*; import java.applet.*; import java.io.IOException; public class Main extends Applet implements Runnable, MouseListener, MouseMotionListener, ActionListener{ Button startButton, UpgRange, UpgDamage; //set up the buttons Color roadCol,startCol,finCol,selGrass,selRoad; //set up the colors Enemy e[][]; Tower t[]; Image towerpic,backpic,roadpic,levelPic; private Image i; private Graphics doubleG; //here is the world 0=grass 1=road 2=start 3=end int world[][],eStartX,eStartY; boolean drawMouse,gameEnd; static boolean start=false; static int gridLength=15; static int round=0; int Mx,My,timer=1500; static int sqrSize=31; int towers=0,towerSelected=-10; static int castleHealth=2000; String levelPath; //choose the level Easy Med or Hard int maxEnemy[] = {5,7,12,20,30,15,50,30,40,60};//number of enimies per round int maxTowers=15;//maximum number of towers allowed static int money =2000,damPrice=600,ranPrice=350,towerPrice=700; //money = the intial ammount of money you start of with //damPrice is the price to increase the damage of a tower //ranPrice is the price to increase the range of a tower public void main(int cH,int mT,int mo,int dP,int rP,int tP,String path,int[] mE)//constructor 1 castleHealth=cH; maxTowers=mT; money=mo; damPrice=dP; ranPrice=rP; towerPrice=tP; String levelPath=path; maxEnemy = mE; buildLevel(); } public void main(int cH,int mT,String path)//basic constructor castleHealth=cH; maxTowers=mT; String levelPath=path; maxEnemy = mE; buildLevel(); } public void init(){ setSize(sqrSize*15+200,sqrSize*15);//set the size of the screen roadCol = new Color(255,216,0);//set the colors for the different objects startCol = new Color(0,38,255); finCol = new Color(255,0,0); selRoad = new Color(242,204,155);//selColor is the color of something when your mouse hovers over it selGrass = new Color(0,190,0); roadpic = getImage(getDocumentBase(),"images/road.jpg"); towerpic = getImage(getDocumentBase(),"images/tower.png"); backpic = getImage(getDocumentBase(),"images/grass.jpg"); levelPic = getImage(getDocumentBase(),"images/level.jpg"); e= new Enemy[maxEnemy.length][];//activates all of the enimies for (int r=0;r<e.length;r++) e[r] = new Enemy[maxEnemy[r]]; t= new Tower[maxTowers]; for (int i=0;i<t.length;i++) t[i]= new Tower();//activates all the towers for (int i=0;i<e.length; i++)//sets all of the enimies starting co ordinates for (int j=0;j<e[i].length;j++) e[i][j] = new Enemy(eStartX,eStartY,world); initButtons();//initialise all the buttons addMouseMotionListener(this); addMouseListener(this); }

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  • Force www. on multi domain site and retain http or https

    - by John Isaacks
    I am using CakePHP which already contains an .htaccess file that looks like: <IfModule mod_rewrite.c> RewriteEngine on RewriteRule ^$ app/webroot/ [L] RewriteRule (.*) app/webroot/$1 [L] </IfModule> I want to force www. (unless it is a subdomain) to avoid duplicate content penalties. It needs to retain http or https Also This application will have multiple domains pointing to it. So the code needs to be able to work with any domain.

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  • "t-sql" tool for csv files?

    - by adolf garlic
    Is there a tool that allows to query files based on the following criteria, and change them? creation date filenames (e.g. filetypeA_YYYYMMDD_data2.blah) file content For the example, the workflow could be the following one: Get all files created between date x and date y, where the filename contains z and the file itself contains value x under column zzz. Update it to be a different value/another column.

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  • Comparing an id to id of different tables rows mysql

    - by jett
    So I am trying to retrieve all interests from someone, and be able to list them. This works with the following query. SELECT *,( SELECT GROUP_CONCAT(interest_id SEPARATOR ",") FROM people_interests WHERE person_id = people.id ) AS interests FROM people WHERE id IN ( SELECT person_id FROM people_interests WHERE interest_id = '.$site->db->clean($_POST['showinterest_id']).' ) ORDER BY lastname, firstname In this one which I am having trouble with, I want to select only those who happen to have their id in the table named volleyballplayers. The table just has an id, person_id, team_id, and date fields. SELECT *,( SELECT GROUP_CONCAT(interest_id SEPARATOR ",") FROM people_interests WHERE person_id = people.id ) AS interests FROM people WHERE id IN ( SELECT person_id FROM people_interests WHERE volleyballplayers.person_id = person_id ) ORDER BY lastname, firstname I just want to make sure that only the people who are in the volleyballplayers table show up, but I am getting an error saying that Unknown column 'volleyballplayers.person_id' in 'where clause' although I am quite sure of the name of table and I know the column is named person_id.

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  • How do I give a Byobu session a name?

    - by Ashimema
    Is there a way to create identifiable Byobu sessions so that when I've got multiple sessions running, the byobu-select-session menu gives me a list of sessions I can recognize, as opposed to non-descript tmux port numbers? In an ideal world, it would be great to be able to both start a session giving it a name and to modify such a session to change a name if it's already running? Is this possible, how?

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  • How to batch retrieve documents with mongoDB?

    - by edude05
    Hello everyone, I have an application that queries data from a mongoDB using the mongoDB C# driver something like this: public void main() { foreach (int i in listOfKey) { list.add(getObjectfromDB(i); } } public myObject getObjFromDb(int primaryKey) { document query = new document(); query["primKey"] = primaryKey; document result= mongo["myDatabase"]["myCollection"].findOne(query); return parseObject(result); } On my local (development) machine to get 100 object this way takes less than a second. However, I recently moved the database to a server on the internet, and this query takes about 30 seconds to execute for the same number of object. Furthermore, looking at the mongoDB log, it seems to open about 8-10 connections to the DB to perform this query. So what I'd like to do is have the query the database for an array of primaryKeys and get them all back at once, then do the parsing in a loop afterwards, using one connection if possible. How could I optimize my query to do so? Thanks, --Michael

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  • How To Implement The Query Side Of CQS in DDD?

    - by Laz
    I have implemented the command side of DDD using the domain model and repositories, but how do I implement the query side? Do I create an entirely new domain model for the UI, and where is this kept in the project structure...in the domain layer, the UI layer, etc? Also, what do I use as my querying mechanism, do I create new repositories specifically for the UI domain objects, something other than repositories, or something else?

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  • Optimize date query for large child tables: GiST or GIN?

    - by Dave Jarvis
    Problem 72 child tables, each having a year index and a station index, are defined as follows: CREATE TABLE climate.measurement_12_013 ( -- Inherited from table climate.measurement_12_013: id bigint NOT NULL DEFAULT nextval('climate.measurement_id_seq'::regclass), -- Inherited from table climate.measurement_12_013: station_id integer NOT NULL, -- Inherited from table climate.measurement_12_013: taken date NOT NULL, -- Inherited from table climate.measurement_12_013: amount numeric(8,2) NOT NULL, -- Inherited from table climate.measurement_12_013: category_id smallint NOT NULL, -- Inherited from table climate.measurement_12_013: flag character varying(1) NOT NULL DEFAULT ' '::character varying, CONSTRAINT measurement_12_013_category_id_check CHECK (category_id = 7), CONSTRAINT measurement_12_013_taken_check CHECK (date_part('month'::text, taken)::integer = 12) ) INHERITS (climate.measurement) CREATE INDEX measurement_12_013_s_idx ON climate.measurement_12_013 USING btree (station_id); CREATE INDEX measurement_12_013_y_idx ON climate.measurement_12_013 USING btree (date_part('year'::text, taken)); (Foreign key constraints to be added later.) The following query runs abysmally slow due to a full table scan: SELECT count(1) AS measurements, avg(m.amount) AS amount FROM climate.measurement m WHERE m.station_id IN ( SELECT s.id FROM climate.station s, climate.city c WHERE -- For one city ... -- c.id = 5182 AND -- Where stations are within an elevation range ... -- s.elevation BETWEEN 0 AND 3000 AND 6371.009 * SQRT( POW(RADIANS(c.latitude_decimal - s.latitude_decimal), 2) + (COS(RADIANS(c.latitude_decimal + s.latitude_decimal) / 2) * POW(RADIANS(c.longitude_decimal - s.longitude_decimal), 2)) ) <= 50 ) AND -- -- Begin extracting the data from the database. -- -- The data before 1900 is shaky; insufficient after 2009. -- extract( YEAR FROM m.taken ) BETWEEN 1900 AND 2009 AND -- Whittled down by category ... -- m.category_id = 1 AND m.taken BETWEEN -- Start date. (extract( YEAR FROM m.taken )||'-01-01')::date AND -- End date. Calculated by checking to see if the end date wraps -- into the next year. If it does, then add 1 to the current year. -- (cast(extract( YEAR FROM m.taken ) + greatest( -1 * sign( (extract( YEAR FROM m.taken )||'-12-31')::date - (extract( YEAR FROM m.taken )||'-01-01')::date ), 0 ) AS text)||'-12-31')::date GROUP BY extract( YEAR FROM m.taken ) The sluggishness comes from this part of the query: m.taken BETWEEN /* Start date. */ (extract( YEAR FROM m.taken )||'-01-01')::date AND /* End date. Calculated by checking to see if the end date wraps into the next year. If it does, then add 1 to the current year. */ (cast(extract( YEAR FROM m.taken ) + greatest( -1 * sign( (extract( YEAR FROM m.taken )||'-12-31')::date - (extract( YEAR FROM m.taken )||'-01-01')::date ), 0 ) AS text)||'-12-31')::date The HashAggregate from the plan shows a cost of 10006220141.11, which is, I suspect, on the astronomically huge side. There is a full table scan on the measurement table (itself having neither data nor indexes) being performed. The table aggregates 237 million rows from its child tables. Question What is the proper way to index the dates to avoid full table scans? Options I have considered: GIN GiST Rewrite the WHERE clause Separate year_taken, month_taken, and day_taken columns to the tables What are your thoughts? Thank you!

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  • How to construct this query? (Ordering by COUNT() and joining with users table)

    - by Andrew
    users table: id-user-other columns scores table: id-user_id-score-other columns They're are more than one rows for each user, but there's only two scores you can have. (0 or 1, == win or loss). So I want to output all the users ordered by the number of wins, and all the users ordered by the numbers of losses. I know how to do this by looping through each user, but I was wondering how to do it with one query. Any help is appreciated!

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  • Avoiding SQL Injection in SQL query with Like Operator using parameters?

    - by MikeJ
    Taking over some code from my predecessor and I found a query that uses the Like operator: SELECT * FROM suppliers WHERE supplier_name like '%'+name+%'; Trying to avoid SQL Injection problem and parameterize this but I am not quite sure how this would be accomplished. Any suggestions ? note, I need a solution for classic ADO.NET - I don't really have the go-ahead to switch this code over to something like LINQ.

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  • How to handle when SSRS does not automatically update fields based on database query?

    - by badpanda
    So I am trying to change the number of fields in my dataset in SSRS and the refresh button is not picking up the added field from the SQL server. The query is definitely returning the correct data, as I have double checked in the server engine itself. Also, I have tried manually adding the field using the SSRS menu, but as soon as I execute it disappears. Any suggestions or similar experiences?

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  • WP plugin: How to split to multiple pages, automatically ?

    - by Tomer
    Hello there. I'm writing a WP plugin, that shows DB records in a table. Because the list is too long, I'd like to split it to multiple pages, based on the same display. I can do that manually with handling URL parameters, and using PHP, but I wanted to know if there's a structed method to to that. http://site.com/list --> records 1-20 http://site.com/list/2 --> records 20-40 Thanks, Tomer

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