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• Database Migration Scripts: Getting from place A to place B

  - by Phil Factor

  We’ll be looking at a typical database ‘migration’ script which uses an unusual technique to migrate existing ‘de-normalised’ data into a more correct form. So, the book-distribution business that uses the PUBS database has gradually grown organically, and has slipped into ‘de-normalisation’ habits. What’s this? A new column with a list of tags or ‘types’ assigned to books. Because books aren’t really in just one category, someone has ‘cured’ the mismatch between the database and the business requirements. This is fine, but it is now proving difficult for their new website that allows searches by tags. Any request for history book really has to look in the entire list of associated tags rather than the ‘Type’ field that only keeps the primary tag. We have other problems. The TypleList column has duplicates in there which will be affecting the reporting, and there is the danger of mis-spellings getting there. The reporting system can’t be persuaded to do reports based on the tags and the Database developers are complaining about the unCoddly things going on in their database. In your version of PUBS, this extra column doesn’t exist, so we’ve added it and put in 10,000 titles using SQL Data Generator. /* So how do we refactor this database? firstly, we create a table of all the tags. */IF  OBJECT_ID('TagName') IS NULL OR OBJECT_ID('TagTitle') IS NULL  BEGIN  CREATE TABLE  TagName (TagName_ID INT IDENTITY(1,1) PRIMARY KEY ,     Tag VARCHAR(20) NOT NULL UNIQUE)  /* ...and we insert into it all the tags from the list (remembering to take out any leading spaces */  INSERT INTO TagName (Tag)     SELECT DISTINCT LTRIM(x.y.value('.', 'Varchar(80)')) AS [Tag]     FROM     (SELECT  Title_ID,          CONVERT(XML, '<list><i>' + REPLACE(TypeList, ',', '</i><i>') + '</i></list>')          AS XMLkeywords          FROM   dbo.titles)g    CROSS APPLY XMLkeywords.nodes('/list/i/text()') AS x ( y )  /* we can then use this table to provide a table that relates tags to articles */  CREATE TABLE TagTitle   (TagTitle_ID INT IDENTITY(1, 1),   [title_id] [dbo].[tid] NOT NULL REFERENCES titles (Title_ID),   TagName_ID INT NOT NULL REFERENCES TagName (Tagname_ID)   CONSTRAINT [PK_TagTitle]       PRIMARY KEY CLUSTERED ([title_id] ASC, TagName_ID)       ON [PRIMARY])        CREATE NONCLUSTERED INDEX idxTagName_ID  ON  TagTitle (TagName_ID)  INCLUDE (TagTitle_ID,title_id)        /* ...and it is easy to fill this with the tags for each title ... */        INSERT INTO TagTitle (Title_ID, TagName_ID)    SELECT DISTINCT Title_ID, TagName_ID      FROM        (SELECT  Title_ID,          CONVERT(XML, '<list><i>' + REPLACE(TypeList, ',', '</i><i>') + '</i></list>')          AS XMLkeywords          FROM   dbo.titles)g    CROSS APPLY XMLkeywords.nodes('/list/i/text()') AS x ( y )    INNER JOIN TagName ON TagName.Tag=LTRIM(x.y.value('.', 'Varchar(80)'))    END    /* That's all there was to it. Now we can select all titles that have the military tag, just to try things out */SELECT Title FROM titles  INNER JOIN TagTitle ON titles.title_ID=TagTitle.Title_ID  INNER JOIN Tagname ON Tagname.TagName_ID=TagTitle.TagName_ID  WHERE tagname.tag='Military'/* and see the top ten most popular tags for titles */SELECT Tag, COUNT(*) FROM titles  INNER JOIN TagTitle ON titles.title_ID=TagTitle.Title_ID  INNER JOIN Tagname ON Tagname.TagName_ID=TagTitle.TagName_ID  GROUP BY Tag ORDER BY COUNT(*) DESC/* and if you still want your list of tags for each title, then here they are */SELECT title_ID, title, STUFF(  (SELECT ','+tagname.tag FROM titles thisTitle    INNER JOIN TagTitle ON titles.title_ID=TagTitle.Title_ID    INNER JOIN Tagname ON Tagname.TagName_ID=TagTitle.TagName_ID  WHERE ThisTitle.title_id=titles.title_ID  FOR XML PATH(''), TYPE).value('.', 'varchar(max)')  ,1,1,'')    FROM titles  ORDER BY title_ID So we’ve refactored our PUBS database without pain. We’ve even put in a check to prevent it being re-run once the new tables are created. Here is the diagram of the new tag relationship We’ve done both the DDL to create the tables and their associated components, and the DML to put the data in them. I could have also included the script to remove the de-normalised TypeList column, but I’d do a whole lot of tests first before doing that. Yes, I’ve left out the assertion tests too, which should check the edge cases and make sure the result is what you’d expect. One thing I can’t quite figure out is how to deal with an ordered list using this simple XML-based technique. We can ensure that, if we have to produce a list of tags, we can get the primary ‘type’ to be first in the list, but what if the entire order is significant? Thank goodness it isn’t in this case. If it were, we might have to revisit a string-splitter function that returns the ordinal position of each component in the sequence. You’ll see immediately that we can create a synchronisation script for deployment from a comparison tool such as SQL Compare, to change the schema (DDL). On the other hand, no tool could do the DML to stuff the data into the new table, since there is no way that any tool will be able to work out where the data should go. We used some pretty hairy code to deal with a slightly untypical problem. We would have to do this migration by hand, and it has to go into source control as a batch. If most of your database changes are to be deployed by an automated process, then there must be a way of over-riding this part of the data synchronisation process to do this part of the process taking the part of the script that fills the tables, Checking that the tables have not already been filled, and executing it as part of the transaction. Of course, you might prefer the approach I’ve taken with the script of creating the tables in the same batch as the data conversion process, and then using the presence of the tables to prevent the script from being re-run. The problem with scripting a refactoring change to a database is that it has to work both ways. If we install the new system and then have to rollback the changes, several books may have been added, or had their tags changed, in the meantime. Yes, you have to script any rollback! These have to be mercilessly tested, and put in source control just in case of the rollback of a deployment after it has been in place for any length of time. I’ve shown you how to do this with the part of the script .. /* and if you still want your list of tags for each title, then here they are */SELECT title_ID, title, STUFF(  (SELECT ','+tagname.tag FROM titles thisTitle    INNER JOIN TagTitle ON titles.title_ID=TagTitle.Title_ID    INNER JOIN Tagname ON Tagname.TagName_ID=TagTitle.TagName_ID  WHERE ThisTitle.title_id=titles.title_ID  FOR XML PATH(''), TYPE).value('.', 'varchar(max)')  ,1,1,'')    FROM titles  ORDER BY title_ID …which would be turned into an UPDATE … FROM script. UPDATE titles SET  typelist= ThisTaglistFROM     (SELECT title_ID, title, STUFF(    (SELECT ','+tagname.tag FROM titles thisTitle      INNER JOIN TagTitle ON titles.title_ID=TagTitle.Title_ID      INNER JOIN Tagname ON Tagname.TagName_ID=TagTitle.TagName_ID    WHERE ThisTitle.title_id=titles.title_ID    ORDER BY CASE WHEN tagname.tag=titles.[type] THEN 1 ELSE 0  END DESC    FOR XML PATH(''), TYPE).value('.', 'varchar(max)')    ,1,1,'')  AS ThisTagList  FROM titles)fINNER JOIN Titles ON f.title_ID=Titles.title_ID You’ll notice that it isn’t quite a round trip because the tags are in a different order, though we’ve managed to make sure that the primary tag is the first one as originally. So, we’ve improved the database for the poor book distributors using PUBS. It is not a major deal but you’ve got to be prepared to provide a migration script that will go both forwards and backwards. Ideally, database refactoring scripts should be able to go from any version to any other. Schema synchronization scripts can do this pretty easily, but no data synchronisation scripts can deal with serious refactoring jobs without the developers being able to specify how to deal with cases like this.

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• dynamic broadcast receiver for connectivity changes

  - by android-dev

  I'm trying to register a dynamic broadcast receiver using the following: BroadcastReceiver connectivityReceiver = new ConnectivityChangeIntentReceiver(); IntentFilter connectivityFilter = new IntentFilter(); filter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION); filter.addAction(android.net.ConnectivityManager.CONNECTIVITY_ACTION); myApplicationContext.registerReceiver(connectivityReceiver, connectivityFilter); but I see my ConnectivityChangeIntentReceiver.onReceive method is not called when I turn off Wifi through settings or change to airplane mode. Has anyone faced a similar problem? I do not want to statically register the receiver in the Manifest file, as I don't want my app to be started by connectivity changes.

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• Dissertation about website and database security - in need of some pointers

  - by ClarkeyBoy

  Hi, I am on my dissertation in my final year at university at the moment. One of the areas I need to research is security - for both websites and for databases. I currently have sections on the following: Website Form security - such as data validation. This section is more about preventing errors made by legitimate users as much as possible rather than stopping hackers, for example comparing a field to a regular expression and giving them meaningful feedback on any errors which did occur so as to stop it happening again. Constraints. For example if a value must be true or false then use a checkbox. If it is likely to be one of several values then use a dropdown or a set of radio boxes, and so on. If the value is unpredictable then use regular expressions to limit what characters they are allowed to enter, and to restrict the length of the string, and sometimes to limit the format (such as for dates / times, post codes and so on). Sometimes you can limit permissions to the form. This is on the occasion that you know exactly who (whether it be peoples names or a group of people - such as administrators or employees) is going to need access to the form. Restricting permissions will stop members of the public from being able to access the form. Symbols or strings which could be used maliciously or cause the website to act incorrectly (such as the script tag) should be filtered out or html encoded. Captcha images can be used to prevent automated systems from filling in and submitting the form. There are some hacks for file uploads - such as using double extensions - which can allow hackers to upload malicious files. Databases (this is nowhere near done yet but the sections I have planned are listed below) SQL statements vs stored procedures Throwing an error when one of the variables contains particular characters or groups of characters (I cant remember what characters they are, but I have seen a message thrown back at me before where I have tried to enter html or something into a text area). SQL Injection - and ways around it, with some examples. Does anyone have any hints and tips on where I could go for some decent, reliable information either about these areas or about other areas of security that I could cover? Thanks in advance. Regards, Richard PS I am a complete newbie when it comes to security, so please be patient with me. If any of the information I have put down is wrong or could be sub-sectioned then please feel free to say so.

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• Multiple database with Spring+Hibernate+JPA

  - by ziftech

  Hi everybody! I'm trying to configure Spring+Hibernate+JPA for work with two databases (MySQL and MSSQL) my datasource-context.xml: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.5.xsd" xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:util="http://www.springframework.org/schema/util"> <!-- Data Source config --> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" p:driverClassName="${local.jdbc.driver}" p:url="${local.jdbc.url}" p:username="${local.jdbc.username}" p:password="${local.jdbc.password}"> </bean> <bean id="dataSourceRemote" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" p:driverClassName="${remote.jdbc.driver}" p:url="${remote.jdbc.url}" p:username="${remote.jdbc.username}" p:password="${remote.jdbc.password}" /> <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager" p:entity-manager-factory-ref="entityManagerFactory" /> <!-- JPA config --> <tx:annotation-driven transaction-manager="transactionManager" /> <bean id="persistenceUnitManager" class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager"> <property name="persistenceXmlLocations"> <list value-type="java.lang.String"> <value>classpath*:config/persistence.local.xml</value> <value>classpath*:config/persistence.remote.xml</value> </list> </property> <property name="dataSources"> <map> <entry key="localDataSource" value-ref="dataSource" /> <entry key="remoteDataSource" value-ref="dataSourceRemote" /> </map> </property> <property name="defaultDataSource" ref="dataSource" /> </bean> <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="jpaVendorAdapter"> <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" p:showSql="true" p:generateDdl="true"> </bean> </property> <property name="persistenceUnitManager" ref="persistenceUnitManager" /> <property name="persistenceUnitName" value="localjpa"/> </bean> <bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" /> </beans> each persistence.xml contains one unit, like this: <persistence-unit name="remote" transaction-type="RESOURCE_LOCAL"> <properties> <property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.DefaultNamingStrategy" /> <property name="hibernate.dialect" value="${remote.hibernate.dialect}" /> <property name="hibernate.hbm2ddl.auto" value="${remote.hibernate.hbm2ddl.auto}" /> </properties> </persistence-unit> PersistenceUnitManager cause following exception: Cannot resolve reference to bean 'persistenceUnitManager' while setting bean property 'persistenceUnitManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'persistenceUnitManager' defined in class path resource [config/datasource-context.xml]: Initialization of bean failed; nested exception is org.springframework.beans.TypeMismatchException: Failed to convert property value of type [java.util.ArrayList] to required type [java.lang.String] for property 'persistenceXmlLocation'; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [java.util.ArrayList] to required type [java.lang.String] for property 'persistenceXmlLocation': no matching editors or conversion strategy found If left only one persistence.xml without list, every works fine but I need 2 units... I also try to find alternative solution for work with two databases in Spring+Hibernate context, so I would appreciate any solution new error after changing to persistenceXmlLocations No single default persistence unit defined in {classpath:config/persistence.local.xml, classpath:config/persistence.remote.xml} UPDATE: I add persistenceUnitName, it works, but only with one unit, still need help UPDATE: thanks, ChssPly76 I changed config files: datasource-context.xml <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.5.xsd" xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:util="http://www.springframework.org/schema/util"> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" p:driverClassName="${local.jdbc.driver}" p:url="${local.jdbc.url}" p:username="${local.jdbc.username}" p:password="${local.jdbc.password}"> </bean> <bean id="dataSourceRemote" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" p:driverClassName="${remote.jdbc.driver}" p:url="${remote.jdbc.url}" p:username="${remote.jdbc.username}" p:password="${remote.jdbc.password}"> </bean> <bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"> <property name="defaultPersistenceUnitName" value="pu1" /> </bean> <bean id="persistenceUnitManager" class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager"> <property name="persistenceXmlLocation" value="${persistence.xml.location}" /> <property name="defaultDataSource" ref="dataSource" /> <!-- problem --> <property name="dataSources"> <map> <entry key="local" value-ref="dataSource" /> <entry key="remote" value-ref="dataSourceRemote" /> </map> </property> </bean> <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="jpaVendorAdapter"> <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" p:showSql="true" p:generateDdl="true"> </bean> </property> <property name="persistenceUnitManager" ref="persistenceUnitManager" /> <property name="persistenceUnitName" value="pu1" /> <property name="dataSource" ref="dataSource" /> </bean> <bean id="entityManagerFactoryRemote" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="jpaVendorAdapter"> <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" p:showSql="true" p:generateDdl="true"> </bean> </property> <property name="persistenceUnitManager" ref="persistenceUnitManager" /> <property name="persistenceUnitName" value="pu2" /> <property name="dataSource" ref="dataSourceRemote" /> </bean> <tx:annotation-driven /> <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager" p:entity-manager-factory-ref="entityManagerFactory" /> <bean id="transactionManagerRemote" class="org.springframework.orm.jpa.JpaTransactionManager" p:entity-manager-factory-ref="entityManagerFactoryRemote" /> </beans> persistence.xml <?xml version="1.0" encoding="UTF-8"?> <persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0"> <persistence-unit name="pu1" transaction-type="RESOURCE_LOCAL"> <properties> <property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.DefaultNamingStrategy" /> <property name="hibernate.dialect" value="${local.hibernate.dialect}" /> <property name="hibernate.hbm2ddl.auto" value="${local.hibernate.hbm2ddl.auto}" /> </properties> </persistence-unit> <persistence-unit name="pu2" transaction-type="RESOURCE_LOCAL"> <properties> <property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.DefaultNamingStrategy" /> <property name="hibernate.dialect" value="${remote.hibernate.dialect}" /> <property name="hibernate.hbm2ddl.auto" value="${remote.hibernate.hbm2ddl.auto}" /> </properties> </persistence-unit> </persistence> Now it builds two entityManagerFactory, but both are for Microsoft SQL Server [main] INFO org.hibernate.ejb.Ejb3Configuration - Processing PersistenceUnitInfo [ name: pu1 ...] [main] INFO org.hibernate.cfg.SettingsFactory - RDBMS: Microsoft SQL Server [main] INFO org.hibernate.ejb.Ejb3Configuration - Processing PersistenceUnitInfo [ name: pu2 ...] [main] INFO org.hibernate.cfg.SettingsFactory - RDBMS: Microsoft SQL Server (but must MySQL) I suggest, that use only dataSource, dataSourceRemote (no substitution) is not worked. That's my last problem

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• Database design for summarized data

  - by holden

  I have a new table I'm going to add to a bunch of other summarized data, basically to take some of the load off by calculating weekly avgs. My question is whether I would be better off with one model over the other. One model with days of the week as a column with an additional column for price or another model as a series of fields for the DOW each taking a price. I'd like to know which would save me in speed and/or headaches? Or at least the trade off. IE. ID OBJECT_ID MON TUE WED THU FRI SAT SUN SOURCE OR ID OBJECT_ID DAYOFWEEK PRICE SOURCE

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• Cross-platform embedded database/key-value store for C#

  - by Arne Claassen

  I'm looking for a fast, embeddable key/value store with cursor semantics over key collections (or a simple embeddable DB) that I can use in .NET and mono. Need it to be open-source, would prefer an MIT or Apache style license over a GPL license. Not opposed to a library that needs bindings to be written, as long as binaries are available for both windows and linux. Options considered: SQLite - has bindings and native implementation, but single-threaded and not all that fast Embedded InnoDB - no .NET bindings i can find and it's GPLv2 Berkley DB - no .NET bindings i can find Tokyo Cabinet - no .NET bindings i can find and problematic to build on windows MadCow Memory-mapped data structures - GPLv2 Is there an option better than the above that i'm missing, or bindings for the above i don't know about?

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• Finding first alphabetic character in a DB2 database field

  - by Paul Alan Taylor

  I'm doing a bit of work which requires me to truncate DB2 character-based fields. Essentially, I need to discard all text which is found at or after the first alphabetic character. e.g. 102048994BLAHBLAHBLAH becomes:- 102048994 In SQL Server, this would be a doddle - PATINDEX would swoop in and save the day. Much celebration would ensue. My problem is that I need to do this in DB2. Worse, the result needs to be used in a join query, also in DB2. I can't find an easy way to do this. Is there a PATINDEX equivalent in DB2? Is there another way to solve this problem? If need be, I'll hardcode 26 chained LOCATE functions to get my result, but if there is a better way, I am all ears.

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• SimpleDB as the main database, examples.

  - by Victor P

  Please, can you give examples of real-life implementations using SimpleDB as the main persistent storage?

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• 2 partitions in a sharded mysql database

  - by ming yeow

  the first one is running at 73% memory utilization. The second one runs at 16% utilization. how can i balance the 2 out?

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• general database modeling and django specific modeling

  - by Shreko

  I'm wondering what is the best way to model something like the following. Lets say my company sells metal bars (parameters/fields are: length, profile_type, quantity etc.) of different profiles, where profiles may be pipe(pipe_diameter, wall_thickness) or hollow_rectangle(base, height, wall_thickness), or maybe some other profile with different parameters. Lets say maximum number of profiles would be 12, each profile having between 2-5 parameters. Should everything be in a single table like table_bars: id, length, quantity, profile_type, pipe_diameter, wall_thickness, base, height, etc.) where profile type would be (pipe, rectangle etc.) or should every shape have its own table with its own parameters and in table_bars keep only id, length, quantity profile_type and profile_id) and are there any django specific issues is multiple tables are the best answer? Thanks

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• Implementing database redundancy with sharded tables

  - by ensnare

  We're looking to implement load balancing by horizontally sharding our tables across a cluster of servers. What are some options to implement live redundancy should a server fail? Would it be effective to do (2) INSERTS instead of one ... one to the target shard, and another to a secondary shard which could be accessed should the primary shard not respond? Or is there a better way? Thanks.

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• Tutorials for .NET database app using SQLite

  - by ChrisC

  I have some MS Access experience, and had a class on console c++ apps, now I am trying to develop my first program. It's a little C# db app. I have the db tables and columns planned and keyed into VS, but that's where I'm stuck. I'm needing C#/VS tutorials that will guide me on configuring relationships, datatyping, etc, on the db so I can get it ready for testing of the schema. The only tutorials I've been able to find either talk about general db basics (ie, not helping me with VS/C#), or about C# communications with an existing SQL db. Thank you. (In case it matters, I'm using the open source System.Data.SQLite (sqlite.phxsoftware.com) for the db. I chose it over SQL Server CE after seeing a comparison between the two. Also I wanted a server-less version of SQL because this little app will be on other people's computers and I want to to do as little support as possible.)

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• Need free English dictionary or Corpus, ultimately for a MySQL database

  - by Chris

  Hey there, I'm trying to find a free downloadable dictionary (or Corpus might be the better word) which I can import into MySQL. I need to words to have the type (noun, verb, adjective) associated with them. Any tips on where I can find one? I found one several years ago that worked nicely, but I no longer have it around. Thanks! Chris

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• Main pricing and support for individual client pricing (Database Architecture ideas help - Rails)

  - by slythic

  Hi all, I have a personal project I'm planning and I came to a small hurdle. I want to have an item with price that will be the default for all clients/users. However, in my business I have some clients that are grandfathered in to some special pricing. In the case of these grandfathered in cases, I'll manually plug their special price in my admin section. Then all they will see is their special pricing while the regular users/clients see the default price. What is the best and simplest way to design the back-end for this? FYI - I'll be using rails as my framework. Many thanks! -Tony

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• Database warehouse design: fact tables and dimension tables

  - by morpheous

  I am building a poor man's data warehouse using a RDBMS. I have identified the key 'attributes' to be recorded as: sex (true/false) demographic classification (A, B, C etc) place of birth date of birth weight (recorded daily): The fact that is being recorded My requirements are to be able to run 'OLAP' queries that allow me to: 'slice and dice' 'drill up/down' the data and generally, be able to view the data from different perspectives After reading up on this topic area, the general consensus seems to be that this is best implemented using dimension tables rather than normalized tables. Assuming that this assertion is true (i.e. the solution is best implemented using fact and dimension tables), I would like to seek some help in the design of these tables. 'Natural' (or obvious) dimensions are: Date dimension Geographical location Which have hierarchical attributes. However, I am struggling with how to model the following fields: sex (true/false) demographic classification (A, B, C etc) The reason I am struggling with these fields is that: They have no obvious hierarchical attributes which will aid aggregation (AFAIA) - which suggest they should be in a fact table They are mostly static or very rarely change - which suggests they should be in a dimension table. Maybe the heuristic I am using above is too crude? I will give some examples on the type of analysis I would like to carryout on the data warehouse - hopefully that will clarify things further. I would like to aggregate and analyze the data by sex and demographic classification - e.g. answer questions like: How does male and female weights compare across different demographic classifications? Which demographic classification (male AND female), show the most increase in weight this quarter. etc. Can anyone clarify whether sex and demographic classification are part of the fact table, or whether they are (as I suspect) dimension tables.? Also assuming they are dimension tables, could someone elaborate on the table structures (i.e. the fields)? The 'obvious' schema: CREATE TABLE sex_type (is_male int); CREATE TABLE demographic_category (id int, name varchar(4)); may not be the correct one.

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• Main pricing and support for custom client pricing (Database Architecture ideas help - Rails)

  - by slythic

  Hi all, I have a personal project I'm planning and I came to a small hurdle. I want to have an item with price that will be the default for all clients/users. However, in my business I have some clients that are grandfathered in to some special pricing. In the case of these grandfathered in cases, I'll manually plug their special price in my admin section. Then all they will see is their special pricing while the regular users/clients see the default price. What is the best and simplest way to design the back-end for this? FYI - I'll be using rails as my framework. Many thanks! -Tony

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• database datatype size

  - by yeeen

  Just to clarify by specifying sth like VARCHAR(45) means it can take up to max 45 characters? I rmb I heard from someone a few years ago that the number in the parathesis doesn't refer to the no of characters, then the person tried to explain to me sth quite complicated which i don't understand n forgot alr. And what is the difference btn CHAR and VARCHAR? I did search ard a bit and see that CHAR gives u the max of the size of the column and it is better to use it if ur data has a fix size and use VARCHAR if ur data size varies. But if it gives u the max of the size of the column of all the data of this col, isn't it better to use it when ur data size varies? Esp if u don't know how big is ur data size gg to be. VARCHAR needs to specify the size (CHAR don't really need right?), isn't it more troublesome?

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• EAV Database Sheme

  - by GLO

  Hello Stackoverflow comunity! I believe that my question has to do with all db guru here! Do you know the EAV DB Scheme ( http://en.wikipedia.org/wiki/Entity-attribute-value_model ) and what they say about the performing of this model. I wonder, If I break this model into smaller tables what the result is? Let's talk about it. I have a db with more that 100K records. A lot of categories and many items ( with different properties per category ) Everything is stored in a EAV. If I try to break this scheme and create for any category a unique table is something that will I have to avoid? Yes, I know that probably I'll have a lot of tables and I'll need to ALTER them if I want to add an extra field, BUT is this so wrong? I have also read that as many tables I have, the db will be populate with more files and this isn't good for any filesystem. Any suggestion? Thank you!

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• how to create database in android

  - by prakrati

  i need step by step procedure for creating a data base in android

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• good database design for localization

  - by rap-uvic

  Hi, I have 3 tables for localization: Locales, ResourceKeys, and Resources. Resources is a many to many table between ResourceKeys and Locales, and stores Resource values for each resource key in multiple languages. Now if I have a table called Event, which needs a localized title and description, how do I best do this? Do I create foreign key columns in Event table which point to ResourceKey IDs each for title and description, or is there a better way?

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• EF4 cross database relationships

  - by Daniel

  Hello all, I was wondering if EF4 support cross-databse relationships? For instance: db1 Author Id Name db2 Posts Id Content db1.Author.Id What ideally I need to do to get this relation in my ef4 model? Do you guys have any idea? Thanks

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• c# reading integer fields from database, returning empty string when reading integer type field

  - by arnoldino

  what is wrong with this code? field="id"; table="MInvMonth"; condition="machine_id=37"; public static String getConditionedField(String field, String table, String condition) try { if (cmd == null) getConnection(); cmd.CommandText = "Select " + field + " from " + table + " where " + condition; SQLiteDataReader reader = cmd.ExecuteReader(); if (reader.HasRows==true) { reader.Read(); string s = reader[0].ToString(); // return first element reader.Close(); return s; } reader.Close(); return null; } catch (Exception e) { MessageBox.Show("Caught exception: " + e.Message+"|"+cmd.CommandText); return null; } I checked the sql statement, it turns the right value. why can't I read it? the returnvalue is "".

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• What relational database innovations have there been in the last 10 years

  - by Simon Munro

  The SQL implementation of relational databases has been around in their current form for something like 25 years (since System R and Ingres). Even the main (loosely adhered to) standard is ANSI-92 (although there were later updates) is a good 15 years old. What innovations can you think of with SQL based databases in the last ten years or so. I am specifically excluding OLAP, Columnar and other non-relational (or at least non SQL) innovations. I also want to exclude 'application server' type features and bundling (like reporting tools) Although the basic approach has remained fairly static, I can think of: Availability Ability to handle larger sets of data Ease of maintenance and configuration Support for more advanced data types (blob, xml, unicode etc) Any others that you can think of?

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• Resources for high performance SQL Server database design

  - by Nathan Ridley

  I'd like some suggestions for online resources (blogs, guides, etc - not forums) to help me become good at designing high performance SQL Server databases that operate with large amounts of data and have heavy loads in terms of data turnover and queries per minute. Suggestions?

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• browse data in Android SQLite Database

  - by Justin C

  Is there a way for an Android user to browse the SQLite databases on his/her phone and view the data in the databases? I use the SoftTrace beta program a lot. It's great but has no way that I can find to download the data it tracks to a PC. Thanks

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