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• Which index is used in select and why?

  - by Lukasz Lysik

  I have the table with zip codes with following columns: id - PRIMARY KEY code - NONCLUSTERED INDEX city When I execute query SELECT TOP 10 * FROM ZIPCodes I get the results sorted by id column. But when I change the query to: SELECT TOP 10 id FROM ZIPCodes I get the results sorted by code column. Again, when I change the query to: SELECT TOP 10 code FROM ZIPCodes I get the results sorted by code column again. And finally when I change to: SELECT TOP 10 id,code FROM ZIPCodes I get the results sorted by id column. My question is in the title of the question. I know which indexes are used in the queries, but my question is, why those indexes are used? I the second query (SELECT TOP 10 id FROM ZIPCodes) wouldn't it be faster if the clusteder index was used? How the query engine chooses which index to use?

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• Selecting data effectively sql

  - by learner135

  Hi, I have a very large table with over 1000 records and 200 columns. When I try to retreive records matching some criteria in the WHERE clause using SELECT statement it takes a lot of time. But most of the time I just want to select a single record that matches the criteria in the WHERE clause rather than all the records. I guess there should be a way to select just a single record and exit which would minimize the retrieval time. I tried ROWNUM=1 in the WHERE clause but it didn't really work cause I guess the engine still checks all the records even after finding the first record matching the WHERE criteria. Is there a way to optimize in case if I want to select just a few records? Thanks in advance. Edit: I am using oracle 10g.

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• How to export javascript generated report to pdf?

  - by Parhs

  Hello... I made a reporting engine with javascript for my project... The problem is with printing.. Although with page-break and css i can produce a good looking report, i want to export that report to a pdf in order to be printed better without ,the url,page title and other stuff that browsers add. Note in Chrome there isnt page setup!!! I am using java for server side. i think sending via ajax the Html of the report somehow and return a url for the pdf report maybe... i am looking for a good tool for this thank you

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• What exactly is saved in SQL Server Statistics? When they get updated? Is SQL Server itself is taking care of them?

  - by Pritesh

  I have been working with SQL Server as a Developer a while. One thing I learnt is SQL Server manages Statistics which help Engine to create optimized execution plan. I could not figure out what exactly is stores in Statistics? (I read it saves Vector, but what Vector?) When/In which scenario SQL Server updates Statistics? How/why some time they go out of sync (old Statistics) In case of old Statistics is a manual DBA/Developer intervention is required or SQL Server Will get them updated. As a DBA/Developer how to find out if Statistics OLD? What should we do?

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• SQL Query: Using IF statement in defining new field

  - by Tofig Hasanov

  I have a table with many fields and additionally several boolean fields (ex: BField1, BField2, BField3 etc.). I need to make a Select Query, which will select all fields except for boolean ones, and a new virtual field (ex: FirstTrueBool) whose value will equal to the name of the first TRUE Boolean Field. For ex: Say I have BField1 = False, BField2 = True, BField3 = true, BField4=false, in that case SQL Query should set [FirstTrueBool] to "BField2". Is that possible? Thank you in advance. P.S. I use Microsoft Access (MDB) Database and Jet Engine.

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• MySQL Query, Date Range From "Blacklist"

  - by erbaker

  I have 2 databases. One is properties and the other is dates. In dates I have associated the land_id and a date (In YYYYMMDD format) which means that the date is not available. I need to formulate a query that a user can specify a start and end date, and then choose a property for which dates are available (not in the date database). How do airline and hotel websites do this kind of logic? I was thinking about taking the date range and picking all days in between and doing a query where the dates do not match and ordering it by number of results, but I can see how that could easily turn into an intense query. CREATE TABLE IF NOT EXISTS `dates` ( `id` int(11) NOT NULL AUTO_INCREMENT, `land_id` int(11) NOT NULL, `date` varchar(255) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=44 ; -- -- Dumping data for table `dates` -- INSERT INTO `dates` (`id`, `land_id`, `date`) VALUES (43, 1, '20100526'), (39, 1, '20100522'), (40, 1, '20100523'), (41, 1, '20100521'), (42, 1, '20100525');

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• Need data on disk drive management by OS: getting base I/O unit size, “sync” option, Direct Memory A

  - by Richard T

  Hello All, I want to ensure I have done all I can to configure a system's disks for serious database use. The three areas I know of (any others?) to be concerned about are: I/O size: the database engine and disk's native size should either match, or the database's native I/O size should be a multiple of the disk's native I/O size. Disks that are capable of Direct Memory Access (eg. IDE) should be configured for it. When a disk says it has written data persistently, it must be so! No keeping it in cache and lying about it. I have been looking for information on how to ensure these are so for CENTOS and Ubuntu, but can't seem to find anything at all! I want to be able to check these things and change them if needed. Any and all input appreciated.

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• High CPU - What to do.

  - by Udi Kantzuker

  I have a high CPU problem with MYSQL using "top" ( linux ) shows cpu peaks of 90%. I was trying to find the source of the problem, turned on general log and slow query log, The slow query log did not find anything. The Db contains a few small tables and one large table that contains almost 100k rows, Database Engine is MyIsam. strange thing i have noticed that on the large table, select, insert are very fast but update takes 0.2 - 0.5 secs. already used optimize and repair and no improvement. the table is being updated frequently, could this be the source of the high CPU% ? What can i do to improve this?

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• How to build custom sqlite with provider under Android?

  - by dr4cul4

  Hi, I have a really strange problem. I need to build custom sqlite3 database engine under Android OS, but I also want to use database provider implementation. Unfortunately when examining sources of Android 1.6 I noticed that it's not so easy. Many classes including android.database.; packages use original provider, also many other parts of framework use android.database.sqlite.; packages directly, wich ofcourse make this abstraction a bit confusing and unnesesary. But going to my question. If there is any way that I could extend database interfaces to use custom implmentation of sqlite (or any other database)?

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• How to improve the speed of a loop containing a sqlalchemy query statement as conditional

  - by LtPinback

  This loop checks if a record is in the sqlite database and builds a list of dictionaries for those records that are missing and then executes a multiple insert statement with the list. This works but it is very slow (at least i think it is slow) as it takes 5 minutes to loop over 3500 queries. I am a complete newbie in python, sqlite and sqlalchemy so I wonder if there is a faster way of doing this. list_dict = [] session = Session() for data in data_list: if session.query(Class_object).filter(Class_object.column_name_01 == data[2]).filter(Class_object.column_name_00 == an_id).count() == 0: list_dict.append({'column_name_00':a_id, 'column_name_01':data[2]}) conn = engine.connect() conn.execute(prices.insert(),list_dict) conn.close() session.close() edit: I moved session = Session() outside the loop. Did not make a difference.

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• Can not connect to SSIS access denied

  - by Pramodtech

  I am facing an issue while connecting to SSIS thru Mangament studio. I'm able to connect to SQL engine, Analysis services but not able to connect to SSIS. I use windows authentication. I tried steps given at http://msdn.microsoft.com/en-us/library/aa337083(SQL.90).aspx but no help. On one of the forum I saw that one needs to restart the MSDTC service, Do I need to do that? bcoz my SQL admin said I need to justify it by assuring that it doesn't affect aything else. Moreover we didn't find way to restart the service, where I can do that? please help. Thanks.

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• Deterministic random number generator with context?

  - by user653133

  I am looking for a seeded random number generator that creates a pool of numbers as a context. It doesn't have to be too good. It is used for a game, but it is important, that each instance of the Game Engine has it's own pool of numbers, so that different game instances or even other parts of the game that use random numbers don't break the deterministic character of the generated numbers. Currently I am using rand() which obviously doesn't have this feature. Are there any c or objective-c generators that are capable of doing what I want? Best regards, Michael

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• what are the various approaches for generating PDFs?

  - by andthereitgoes

  I have an idea for an app that would take some flash content which contains graphics and images like various geometric shapes and polygons and some random images and convert them to PDF. Also, since I envision this app to be used my multiple users I want this process to be quick and scalable. One possible solution I could think of is have a small flash client with the capability of assembling the above mentioned graphics and images. Generate some sort of XML, send it to a server running a Java process which could render the PDF using iText. I was wondering what are the other possible ways to do it or the best practices. Technology isn't an issue; open source or commercial. I am looking for ideas to make the process fast and scalable. Most importantly, I don't want the back end server side PDF render engine to constraint the flash client capabilities. I would appreciate if you could share your tech stack idea. Thanks a lot!

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• No difference between nullable:true and nullable:false in Grails 1.3.6?

  - by knorv

  The following domain model definition .. class Test { String a String b static mapping = { version(false) table("test_table") a(nullable: false) b(nullable: true) } } .. yields the following MySQL schema .. CREATE TABLE test_table ( id bigint(20) NOT NULL AUTO_INCREMENT, a varchar(255) NOT NULL, b varchar(255) NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; Please note that a and b get identical MySQL column definitions despite the fact a is defined as non-nullable and b is nullable in the GORM mappings. What am I doing wrong? I'm running Grails 1.3.6.

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• Velocity Templates - New Line.

  - by LdSe

  Hello all, I've been working with Apache's Velocity engine and a custom template. The thing is, that I haven't been able to generate a String with the corresponding line breaks. I tried almost everything that I found, such as using $esc.n and $esc.newline (I'm already using escape tools on my project) but it seems that the version I'm currently using doesn't support it (1.4), checked if putting '\n', '\\n' and even '\\\n' would work, but same thing. Does anyone have any solution to this? Thanks a lot in advance! Regards.

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• My Apache doesn't execute PHP code with <? ?> Tag [closed]

  - by amateurs

  Possible Duplicate: How to enable PHP short tags ? I am using Apache Friends XAMPP (Basis Package) version 1.7.3 Apache 2.2.14 (IPV6 enabled) MySQL 5.1.41 (Community Server) with PBXT engine 1.0.09-rc PHP 5.3.1 (PEAR, Mail_Mime, MDB2, Zend) and i am running php files, that i code with <? ?> tags not <?php ?>. but the apache server won't execute my code, but if i try with <?php ?> tags, the code works. Anyone know how to enable the server to execute php code with <? ?> tags ?

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• Why is UDP + a software reliable ordering system faster than TCP?

  - by Ricket

  Some games today use a network system that transmits messages over UDP, and ensures that the messages are reliable and ordered. For example, RakNet is a popular game network engine. It uses only UDP for its connections, and has a whole system to ensure that packets can be reliable and ordered if you so choose. My basic question is, what's up with that? Isn't TCP the same thing as ordered, reliable UDP? What makes it so much slower that people have to basically reinvent the wheel?

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• Debugging (displaying) SQL command sent to the db by SQLAlchemy

  - by morpheous

  I have an ORM class called Person, which wraps around a person table: After setting up the connection to the db etc, I run the ff statement. people = session.query(Person).all() The person table does not contain any data (as yet), so when I print the variable people, I get an empty list. I renamed the table referred to in my ORM class People, to people_foo (which does not exist). I then run the script again. I was surprised that no exception was thrown when attempting to access a table that does not exist. I therefore have the following 2 questions: How may I setup SQLAlchemy so that it propagates db errors back to the script? How may I view (i.e. print) the SQL that is being sent to the db engine If it helps, I am using PostgreSQL as the db

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• phpMyAdmin "No database selected" MySQL

  - by user1751660

  I downloaded a MySQL backup file and promptly imported into MAMP's phpMyAdmin. I got this return: Error SQL query: -- -- Database: `mysql` -- -- -------------------------------------------------------- -- -- Table structure for table `columns_priv` -- CREATE TABLE IF NOT EXISTS `columns_priv` ( `Host` CHAR( 60 ) COLLATE utf8_bin NOT NULL DEFAULT '', `Db` CHAR( 64 ) COLLATE utf8_bin NOT NULL DEFAULT '', `User` CHAR( 16 ) COLLATE utf8_bin NOT NULL DEFAULT '', `Table_name` CHAR( 64 ) COLLATE utf8_bin NOT NULL DEFAULT '', `Column_name` CHAR( 64 ) COLLATE utf8_bin NOT NULL DEFAULT '', `Timestamp` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP , `Column_priv` SET( 'Select', 'Insert', 'Update', 'References' ) CHARACTER SET utf8 NOT NULL DEFAULT '', PRIMARY KEY ( `Host` , `Db` , `User` , `Table_name` , `Column_name` ) ) ENGINE = MYISAM DEFAULT CHARSET = utf8 COLLATE = utf8_bin COMMENT = 'Column privileges'; MySQL said: #1046 - No database selected I did not alter the .sql file at all. Any hints on how i can get this puppy going locally? Thanks!

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• SQL CREATE TABLE Error

  - by Adam M-W

  Hi, I've been stuck on this one simple(ish) thing for the last 1/2 hour so I thought I might try to get a quick answer here. What exactly is incorrect about my SQL syntax, assuming I'm using mysql 5.1 CREATE TABLE 'users' ( 'id' MEDIUMINT(8) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY, 'username' VARCHAR(20) NOT NULL, 'password' VARCHAR(40) NOT NULL, 'salt' VARCHAR(40) DEFAULT NULL, 'email' VARCHAR(80) NOT NULL, 'created_on' INT(11) UNSIGNED NOT NULL, 'last_login' INT(11) UNSIGNED DEFAULT NULL, 'active' TINYINT(1) UNSIGNED DEFAULT NULL, ) ENGINE InnoDB; Also, does anyone have any good tutorials about how to use Zend_Auth for complete noobs? Thanks.

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• Looking for a mobile platform to view vector data and use it like a simple map

  - by Orchestrator

  I would like to develop or use an existing platform that will allow me to view custom vector data and use it as a map on mobile phones such as Android/IPhone (Maybe even WP7). I'm hoping that there's already a good infrastructure for what I need so I would not need to develop a whole infrastructure by myself. In Conclusion - Is there any existing platform that may answer my needs? If not, how would you guys suggest I should begin? How should I save my vector data? How could I read it? Should I view it with a graphics engine like OpenGL? Is there any chance this solution could be cross-platform? I know that it's possible since it was already done with apps like Waze. And it works the same on iOS and Android. Thanks!

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• Where is the best place to start learning Java Socket Programming?

  - by MarcoBoomTing

  I wish to create a Java Socket server which can be connected to using Javascript and/or Flash. I have experience in Connecting to sockets in flash, and using a comet like system in Ajax. I wish to make a live communication system, which will intale multiple connections to the server from various clients, needing almost instant communication between peers. I coded a system like this in PHP but I want to convert it to Java, simply because I don't want the PHP engine to be tied up on this Sever, as it serves all the web stuff normally on the site, and i've heard is more powerful for this sort of thing. Just looking for advice on where I can start learning how to write this sort of system using Java? I have previous coding experience in PHP, Javascript, Adobe Air and AS3 if That helps?

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• Calling Google's Custom Search API via Python

  - by user353829

  I am writing in Python a module that will query Google's Custom Search API and return all listings of domain 'example.com' I Have been reading instructions at https://code.google.com/apis/customsearch/v1/getting_started.html and am a little stumped at the moment. Are my assumptions listed below correct? For example, to search for results that has 'example.com' in the URL, the query is: *'https://www.googleapis.com/customsearch/v1?key=my_key&cx=017576662512468239146:omuauf_lfve&q=site:example.com*' *key=my_key*: value of key given by google cx=017576662512468239146: name of the search engine (google)? *omuauf_lfve*: I have no idea what this is q=site:example.com: This should return all results with 'example.com'; e.g. www.a.example.com, b.example.com, example .com

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• Comparison tool with easy line insertion

  - by Miro Kropacek

  Back in good old days I used to use a tool for file comparison with one incredible feature -- you open file1, file2, see a difference, no magic here. But then you could insert an empty line(s) into file1 with one keyboard combo and into file2 with another keyboard combo. So you could easily adjust how are C / asm function aligned in case diff engine failed to recognize similar stuff. Of course, after the adjust (insertion / removal of one or more lines in either file) whole diff was "recalculated". I fail to find similar feature in diff, KDiff, ... I'd prefer Linux app but I'm OK with Windows app as last resort... Thanks for any hint!

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• how to google a symbol keyword like "$?"

  - by ZhengZhiren

  i saw a trick in a book: in a linux shell, we can use &? to get the return value of a command. For example,we run a command,if it exit normally, the return value is 0. And then we type $?,we will get 0 in the screen. i want to google this kind of usage, so i have to type these two symbol $? in the search blank.But the search engine just return nothing to me... i have looked at the google help page, but still can't find a solution. so my question is: how can i search with this kind of keyword. or if you can give me some advise of the usage of $? or sort of thing, that will be also appreciated.

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