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  • Is "campaign_$" a bad name for a SQL column?

    - by Summer
    PostgreSQL has allowed me to name a column "campaign_$". I like the name because it's short and to the point, and other potential names like "campaign_receipts" seem longer and less clear. BUT, I wonder if I'll eventually regret putting a $ symbol in a column name, either in PHP or in some other distant part of the architecture. Should I just stick to letters and underscores? Thanks!

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  • MYSQL autoincrement a column or just have an integer, difference?

    - by David19801
    Hi, If I have a column, set as primary index, and set as INT. If I don't set it as auto increment and just insert random integers which are unique into it, does that slow down future queries compared to autincrementing? Does it speed things up if I run OPTIMIZE on a table with its primary and only index as INT? (assuming only 2 columns, and second column is just some INT value) (the main worry is the upper limit on the autoincrement as theres lots of adds and deletes in my table)

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  • Django database - how to add this column in raw SQL.

    - by alex
    Suppose I have my models set up already. class books(models.Model): title = models.CharField... ISBN = models.Integer... What if I want to add this column to my table? user = models.ForeignKey(User, unique=True) How would I write the raw SQL in my database so that this column works?

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  • A Look at the GridView's New Sorting Styles in ASP.NET 4.0

    Like every Web control in the ASP.NET toolbox, the GridView includes a variety of style-related properties, including CssClass, Font, ForeColor, BackColor, Width, Height, and so on. The GridView also includes style properties that apply to certain classes of rows in the grid, such as RowStyle, AlternatingRowStyle, HeaderStyle, and PagerStyle. Each of these meta-style properties offer the standard style properties (CssClass, Font, etc.) as subproperties. In ASP.NET 4.0, Microsoft added four new style properties to the GridView control: SortedAscendingHeaderStyle, SortedAscendingCellStyle, SortedDescendingHeaderStyle, and SortedDescendingCellStyle. These four properties are meta-style properties like RowStyle and HeaderStyle, but apply to column of cells rather than a row. These properties only apply when the GridView is sorted - if the grid's data is sorted in ascending order then the SortedAscendingHeaderStyle and SortedAscendingCellStyle properties define the styles for the column the data is sorted by. The SortedDescendingHeaderStyle and SortedDescendingCellStyle properties apply to the sorted column when the results are sorted in descending order. These four new properties make it easier to customize the appearance of the column by which the data is sorted. Using these properties along with a touch of Cascading Style Sheets (CSS) it is possible to add up and down arrows to the sorted column's header to indicate whether the data is sorted in ascending or descending order. Likewise, these properties can be used to shade the sorted column or make its text bold. This article shows how to use these four new properties to style the sorted column. Read on to learn more! Read More >

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  • A Look at the GridView's New Sorting Styles in ASP.NET 4.0

    Like every Web control in the ASP.NET toolbox, the GridView includes a variety of style-related properties, including CssClass, Font, ForeColor, BackColor, Width, Height, and so on. The GridView also includes style properties that apply to certain classes of rows in the grid, such as RowStyle, AlternatingRowStyle, HeaderStyle, and PagerStyle. Each of these meta-style properties offer the standard style properties (CssClass, Font, etc.) as subproperties. In ASP.NET 4.0, Microsoft added four new style properties to the GridView control: SortedAscendingHeaderStyle, SortedAscendingCellStyle, SortedDescendingHeaderStyle, and SortedDescendingCellStyle. These four properties are meta-style properties like RowStyle and HeaderStyle, but apply to column of cells rather than a row. These properties only apply when the GridView is sorted - if the grid's data is sorted in ascending order then the SortedAscendingHeaderStyle and SortedAscendingCellStyle properties define the styles for the column the data is sorted by. The SortedDescendingHeaderStyle and SortedDescendingCellStyle properties apply to the sorted column when the results are sorted in descending order. These four new properties make it easier to customize the appearance of the column by which the data is sorted. Using these properties along with a touch of Cascading Style Sheets (CSS) it is possible to add up and down arrows to the sorted column's header to indicate whether the data is sorted in ascending or descending order. Likewise, these properties can be used to shade the sorted column or make its text bold. This article shows how to use these four new properties to style the sorted column. Read on to learn more! Read More >

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  • July, the 31 Days of SQL Server DMO’s – Day 18 (sys.dm_io_virtual_file_stats)

    - by Tamarick Hill
    The sys.dm_io_virtual_file_stats Dynamic Management Function is used to return IO statistic information about each of your database files on your server. As input parameters, this function takes a database_id and a file_id. If you want to return IO statistic information for all files, you can simply pass in NULL values for both of these. Let’s have a look at this function  and examine its results: SELECT db_name(database_id) DatabaseName, * FROM sys.dm_io_virtual_file_stats(NULL, NULL) The first column in the result set is the DatabaseName which is just a column I created using the db_name() system function and the database_id column from this function. Next we have a file_id which represent the ID for the file, whether it be a data file or transaction log file. The ‘sample_ms’ column represents the total time in milliseconds that the instance has been up and running. Next we have the ‘num_of_reads’, ‘num_of_bytes_read’, and later ‘num_of_writes’, and ‘num_of_bytes_written’. These columns represent the number of reads or writes and number of bytes read or written against a particular file. These columns are beneficial when determining how often a particular file is being accessed. The ‘io_stall_read_ms’ and io_stall_write_ms’ columns each represent the the total time in milliseconds that users have had to wait for reads or writes against a file respectively. The ‘io_stall’ column is the sum of both read and write io stalls. The ‘size_on_disk_bytes’ column represents the size of the respective file on your disk subsystem. Lastly the ‘file_handle’ column is simply the Windows File handle. This Dynamic Management Function is useful when you are needing to analyze your database files for the purposes of segregating high IO databases. This DMF gives you a good view of which of your database files are being accessed the most and which ones may be generating the largest IO stalls. These could be your best candidates for moving into separate IO channels. For more information about this DMF, please see the below Books Online link: http://msdn.microsoft.com/en-us/library/ms190326.aspx Follow me on Twitter @PrimeTimeDBA

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  • LASTDATE dates arguments and upcoming events #dax #tabular #powerpivot

    - by Marco Russo (SQLBI)
    Recently I had to write a DAX formula containing a LASTDATE within the logical condition of a FILTER: I found that its behavior was not the one I expected and I further investigated. At the end, I wrote my findings in this article on SQLBI, which can be applied to any Time Intelligence function with a <dates> argument.The key point is that when you write LASTDATE( table[column] )in reality you obtain something like LASTDATE( CALCULATETABLE( VALUES( table[column] ) ) )which converts an existing row context into a filter context.Thus, if you have something like FILTER( table, table[column] = LASTDATE( table[column] ) the FILTER will return all the rows of table, whereas you probably want to use FILTER( table, table[column] = LASTDATE( VALUES( table[column] ) ) )so that the existing filter context before executing FILTER is used to get the result from VALUES( table[column] ), avoiding the automatic expansion that would include a CALCULATETABLE that would hide the existing filter context.If after reading the article you want to get more insights, read the Jeffrey Wang's post here.In these days I'm speaking at SQLRally Nordic 2012 in Copenhagen and I will be in Cologne (Germany) next week for a SSAS Tabular Workshop, whereas Alberto will teach the same workshop in Amsterdam one week later. Both workshops still have seats available and the Amsterdam's one is still in early bird discount until October 3rd!Then, in November I expect to meet many blog readers at PASS Summit 2012 in Seattle and I hope to find the time to write other article on interesting things on Tabular and PowerPivot. Stay tuned!

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  • Instructor Insight: Dealing with Columns in Oracle JD Edwards Enterprise One Tools Release 9.1

    - by Breanne Cooley
    Oracle JD Edwards Enterprise One Tools Release  9.1 has many new features that will help end users be more efficient in their daily jobs. For example, hiding grid columns is now as easy as a left-mouse click. In earlier releases, users could click on the ‘Customize Grid’ link but still had to do several more clicks to hide or show a column . The following example shows how easy this new feature is to use. First, right-mouse click on the column you want to hide; for example the ‘Long Address’ column. The column is now hidden. Second, right-mouse over on any of the columns to show the ‘Unhide’ option. After you select ‘Unhide’, the hidden column is shown. You can then select the column to show, or unhide, the column. This new feature and others are covered in the JD Edwards EnterpriseOne System Administration Rel 9.x course, which has been updated to reflect the new release. Hope to see you in class! -Randy Richeson, Senior Principal Instructor, Oracle University

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  • Modifying value of "Rating" column within Explorer for arbitrary file types.

    - by Fake Name
    Basically, I have a large body of assorted media (text, images, flash files, archives, folders, etc...) and I'm attempting to organize it. Windows Explorer has a rating column, but there seems to be no way to modify the rating of the files short of opening them in their type-specific software (e.g. Media player, or Photo viewer). However, this does not work when the file is of an unsupported type (.rar, .swf ...), or a directory. I'd be more than willing to consider a file-manager replacement (I've alreadly looked at quite a few, Directory Opus, Total Commander, etc...), or even a solution that stores the rating metadata in a hidden file in each folder, or a separate database. The one real critical requirement is the ability to sort by rating, and being filetype-agnostic. Basically, is there any way to categorize a large collection of assorted files by rating that will work with any file type, including directories? - Ideally, there would be an easy way to add arbitrary columns to windows explorer, and edit them directly. However, there seems to be no way to do this. The rating column is the next best thing.

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  • Difference between LASTDATE and MAX for semi-additive measures in #DAX

    - by Marco Russo (SQLBI)
    I recently wrote an article on SQLBI about the semi-additive measures in DAX. I included the formulas common calculations and there is an interesting point that worth a longer digression: the difference between LASTDATE and MAX (which is similar to FIRSTDATE and MIN – I just describe the former, for the latter just replace the correspondent names). LASTDATE is a dax function that receives an argument that has to be a date column and returns the last date active in the current filter context. Apparently, it is the same value returned by MAX, which returns the maximum value of the argument in the current filter context. Of course, MAX can receive any numeric type (including date), whereas LASTDATE only accepts a column of type date. But overall, they seems identical in the result. However, the difference is a semantic one. In fact, this expression: LASTDATE ( 'Date'[Date] ) could be also rewritten as: FILTER ( VALUES ( 'Date'[Date] ), 'Date'[Date] = MAX ( 'Date'[Date] ) ) LASTDATE is a function that returns a table with a single column and one row, whereas MAX returns a scalar value. In DAX, any expression with one row and one column can be automatically converted into the corresponding scalar value of the single cell returned. The opposite is not true. So you can use LASTDATE in any expression where a table or a scalar is required, but MAX can be used only where a scalar expression is expected. Since LASTDATE returns a table, you can use it in any expression that expects a table as an argument, such as COUNTROWS. In fact, you can write this expression: COUNTROWS ( LASTDATE ( 'Date'[Date] ) ) which will always return 1 or BLANK (if there are no dates active in the current filter context). You cannot pass MAX as an argument of COUNTROWS. You can pass to LASTDATE a reference to a column or any table expression that returns a column. The following two syntaxes are semantically identical: LASTDATE ( 'Date'[Date] ) LASTDATE ( VALUES ( 'Date'[Date] ) ) The result is the same and the use of VALUES is not required because it is implicit in the first syntax, unless you have a row context active. In that case, be careful that using in a row context the LASTDATE function with a direct column reference will produce a context transition (the row context is transformed into a filter context) that hides the external filter context, whereas using VALUES in the argument preserve the existing filter context without applying the context transition of the row context (see the columns LastDate and Values in the following query and result). You can use any other table expressions (including a FILTER) as LASTDATE argument. For example, the following expression will always return the last date available in the Date table, regardless of the current filter context: LASTDATE ( ALL ( 'Date'[Date] ) ) The following query recap the result produced by the different syntaxes described. EVALUATE     CALCULATETABLE(         ADDCOLUMNS(              VALUES ('Date'[Date] ),             "LastDate", LASTDATE( 'Date'[Date] ),             "Values", LASTDATE( VALUES ( 'Date'[Date] ) ),             "Filter", LASTDATE( FILTER ( VALUES ( 'Date'[Date] ), 'Date'[Date] = MAX ( 'Date'[Date] ) ) ),             "All", LASTDATE( ALL ( 'Date'[Date] ) ),             "Max", MAX( 'Date'[Date] )         ),         'Date'[Calendar Year] = 2008     ) ORDER BY 'Date'[Date] The LastDate columns repeat the current date, because the context transition happens within the ADDCOLUMNS. The Values column preserve the existing filter context from being replaced by the context transition, so the result corresponds to the last day in year 2008 (which is filtered in the external CALCULATETABLE). The Filter column works like the Values one, even if we use the FILTER instead of the LASTDATE approach. The All column shows the result of LASTDATE ( ALL ( ‘Date’[Date] ) ) that ignores the filter on Calendar Year (in fact the date returned is in year 2010). Finally, the Max column shows the result of the MAX formula, which is the easiest to use and only don’t return a table if you need it (like in a filter argument of CALCULATE or CALCULATETABLE, where using LASTDATE is shorter). I know that using LASTDATE in complex expressions might create some issue. In my experience, the fact that a context transition happens automatically in presence of a row context is the main reason of confusion and unexpected results in DAX formulas using this function. For a reference of DAX formulas using MAX and LASTDATE, read my article about semi-additive measures in DAX.

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  • Inheritance Mapping Strategies with Entity Framework Code First CTP5 Part 1: Table per Hierarchy (TPH)

    - by mortezam
    A simple strategy for mapping classes to database tables might be “one table for every entity persistent class.” This approach sounds simple enough and, indeed, works well until we encounter inheritance. Inheritance is such a visible structural mismatch between the object-oriented and relational worlds because object-oriented systems model both “is a” and “has a” relationships. SQL-based models provide only "has a" relationships between entities; SQL database management systems don’t support type inheritance—and even when it’s available, it’s usually proprietary or incomplete. There are three different approaches to representing an inheritance hierarchy: Table per Hierarchy (TPH): Enable polymorphism by denormalizing the SQL schema, and utilize a type discriminator column that holds type information. Table per Type (TPT): Represent "is a" (inheritance) relationships as "has a" (foreign key) relationships. Table per Concrete class (TPC): Discard polymorphism and inheritance relationships completely from the SQL schema.I will explain each of these strategies in a series of posts and this one is dedicated to TPH. In this series we'll deeply dig into each of these strategies and will learn about "why" to choose them as well as "how" to implement them. Hopefully it will give you a better idea about which strategy to choose in a particular scenario. Inheritance Mapping with Entity Framework Code FirstAll of the inheritance mapping strategies that we discuss in this series will be implemented by EF Code First CTP5. The CTP5 build of the new EF Code First library has been released by ADO.NET team earlier this month. EF Code-First enables a pretty powerful code-centric development workflow for working with data. I’m a big fan of the EF Code First approach, and I’m pretty excited about a lot of productivity and power that it brings. When it comes to inheritance mapping, not only Code First fully supports all the strategies but also gives you ultimate flexibility to work with domain models that involves inheritance. The fluent API for inheritance mapping in CTP5 has been improved a lot and now it's more intuitive and concise in compare to CTP4. A Note For Those Who Follow Other Entity Framework ApproachesIf you are following EF's "Database First" or "Model First" approaches, I still recommend to read this series since although the implementation is Code First specific but the explanations around each of the strategies is perfectly applied to all approaches be it Code First or others. A Note For Those Who are New to Entity Framework and Code-FirstIf you choose to learn EF you've chosen well. If you choose to learn EF with Code First you've done even better. To get started, you can find a great walkthrough by Scott Guthrie here and another one by ADO.NET team here. In this post, I assume you already setup your machine to do Code First development and also that you are familiar with Code First fundamentals and basic concepts. You might also want to check out my other posts on EF Code First like Complex Types and Shared Primary Key Associations. A Top Down Development ScenarioThese posts take a top-down approach; it assumes that you’re starting with a domain model and trying to derive a new SQL schema. Therefore, we start with an existing domain model, implement it in C# and then let Code First create the database schema for us. However, the mapping strategies described are just as relevant if you’re working bottom up, starting with existing database tables. I’ll show some tricks along the way that help you dealing with nonperfect table layouts. Let’s start with the mapping of entity inheritance. -- The Domain ModelIn our domain model, we have a BillingDetail base class which is abstract (note the italic font on the UML class diagram below). We do allow various billing types and represent them as subclasses of BillingDetail class. As for now, we support CreditCard and BankAccount: Implement the Object Model with Code First As always, we start with the POCO classes. Note that in our DbContext, I only define one DbSet for the base class which is BillingDetail. Code First will find the other classes in the hierarchy based on Reachability Convention. public abstract class BillingDetail  {     public int BillingDetailId { get; set; }     public string Owner { get; set; }             public string Number { get; set; } } public class BankAccount : BillingDetail {     public string BankName { get; set; }     public string Swift { get; set; } } public class CreditCard : BillingDetail {     public int CardType { get; set; }                     public string ExpiryMonth { get; set; }     public string ExpiryYear { get; set; } } public class InheritanceMappingContext : DbContext {     public DbSet<BillingDetail> BillingDetails { get; set; } } This object model is all that is needed to enable inheritance with Code First. If you put this in your application you would be able to immediately start working with the database and do CRUD operations. Before going into details about how EF Code First maps this object model to the database, we need to learn about one of the core concepts of inheritance mapping: polymorphic and non-polymorphic queries. Polymorphic Queries LINQ to Entities and EntitySQL, as object-oriented query languages, both support polymorphic queries—that is, queries for instances of a class and all instances of its subclasses, respectively. For example, consider the following query: IQueryable<BillingDetail> linqQuery = from b in context.BillingDetails select b; List<BillingDetail> billingDetails = linqQuery.ToList(); Or the same query in EntitySQL: string eSqlQuery = @"SELECT VAlUE b FROM BillingDetails AS b"; ObjectQuery<BillingDetail> objectQuery = ((IObjectContextAdapter)context).ObjectContext                                                                          .CreateQuery<BillingDetail>(eSqlQuery); List<BillingDetail> billingDetails = objectQuery.ToList(); linqQuery and eSqlQuery are both polymorphic and return a list of objects of the type BillingDetail, which is an abstract class but the actual concrete objects in the list are of the subtypes of BillingDetail: CreditCard and BankAccount. Non-polymorphic QueriesAll LINQ to Entities and EntitySQL queries are polymorphic which return not only instances of the specific entity class to which it refers, but all subclasses of that class as well. On the other hand, Non-polymorphic queries are queries whose polymorphism is restricted and only returns instances of a particular subclass. In LINQ to Entities, this can be specified by using OfType<T>() Method. For example, the following query returns only instances of BankAccount: IQueryable<BankAccount> query = from b in context.BillingDetails.OfType<BankAccount>() select b; EntitySQL has OFTYPE operator that does the same thing: string eSqlQuery = @"SELECT VAlUE b FROM OFTYPE(BillingDetails, Model.BankAccount) AS b"; In fact, the above query with OFTYPE operator is a short form of the following query expression that uses TREAT and IS OF operators: string eSqlQuery = @"SELECT VAlUE TREAT(b as Model.BankAccount)                       FROM BillingDetails AS b                       WHERE b IS OF(Model.BankAccount)"; (Note that in the above query, Model.BankAccount is the fully qualified name for BankAccount class. You need to change "Model" with your own namespace name.) Table per Class Hierarchy (TPH)An entire class hierarchy can be mapped to a single table. This table includes columns for all properties of all classes in the hierarchy. The concrete subclass represented by a particular row is identified by the value of a type discriminator column. You don’t have to do anything special in Code First to enable TPH. It's the default inheritance mapping strategy: This mapping strategy is a winner in terms of both performance and simplicity. It’s the best-performing way to represent polymorphism—both polymorphic and nonpolymorphic queries perform well—and it’s even easy to implement by hand. Ad-hoc reporting is possible without complex joins or unions. Schema evolution is straightforward. Discriminator Column As you can see in the DB schema above, Code First has to add a special column to distinguish between persistent classes: the discriminator. This isn’t a property of the persistent class in our object model; it’s used internally by EF Code First. By default, the column name is "Discriminator", and its type is string. The values defaults to the persistent class names —in this case, “BankAccount” or “CreditCard”. EF Code First automatically sets and retrieves the discriminator values. TPH Requires Properties in SubClasses to be Nullable in the Database TPH has one major problem: Columns for properties declared by subclasses will be nullable in the database. For example, Code First created an (INT, NULL) column to map CardType property in CreditCard class. However, in a typical mapping scenario, Code First always creates an (INT, NOT NULL) column in the database for an int property in persistent class. But in this case, since BankAccount instance won’t have a CardType property, the CardType field must be NULL for that row so Code First creates an (INT, NULL) instead. If your subclasses each define several non-nullable properties, the loss of NOT NULL constraints may be a serious problem from the point of view of data integrity. TPH Violates the Third Normal FormAnother important issue is normalization. We’ve created functional dependencies between nonkey columns, violating the third normal form. Basically, the value of Discriminator column determines the corresponding values of the columns that belong to the subclasses (e.g. BankName) but Discriminator is not part of the primary key for the table. As always, denormalization for performance can be misleading, because it sacrifices long-term stability, maintainability, and the integrity of data for immediate gains that may be also achieved by proper optimization of the SQL execution plans (in other words, ask your DBA). Generated SQL QueryLet's take a look at the SQL statements that EF Code First sends to the database when we write queries in LINQ to Entities or EntitySQL. For example, the polymorphic query for BillingDetails that you saw, generates the following SQL statement: SELECT  [Extent1].[Discriminator] AS [Discriminator],  [Extent1].[BillingDetailId] AS [BillingDetailId],  [Extent1].[Owner] AS [Owner],  [Extent1].[Number] AS [Number],  [Extent1].[BankName] AS [BankName],  [Extent1].[Swift] AS [Swift],  [Extent1].[CardType] AS [CardType],  [Extent1].[ExpiryMonth] AS [ExpiryMonth],  [Extent1].[ExpiryYear] AS [ExpiryYear] FROM [dbo].[BillingDetails] AS [Extent1] WHERE [Extent1].[Discriminator] IN ('BankAccount','CreditCard') Or the non-polymorphic query for the BankAccount subclass generates this SQL statement: SELECT  [Extent1].[BillingDetailId] AS [BillingDetailId],  [Extent1].[Owner] AS [Owner],  [Extent1].[Number] AS [Number],  [Extent1].[BankName] AS [BankName],  [Extent1].[Swift] AS [Swift] FROM [dbo].[BillingDetails] AS [Extent1] WHERE [Extent1].[Discriminator] = 'BankAccount' Note how Code First adds a restriction on the discriminator column and also how it only selects those columns that belong to BankAccount entity. Change Discriminator Column Data Type and Values With Fluent API Sometimes, especially in legacy schemas, you need to override the conventions for the discriminator column so that Code First can work with the schema. The following fluent API code will change the discriminator column name to "BillingDetailType" and the values to "BA" and "CC" for BankAccount and CreditCard respectively: protected override void OnModelCreating(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder) {     modelBuilder.Entity<BillingDetail>()                 .Map<BankAccount>(m => m.Requires("BillingDetailType").HasValue("BA"))                 .Map<CreditCard>(m => m.Requires("BillingDetailType").HasValue("CC")); } Also, changing the data type of discriminator column is interesting. In the above code, we passed strings to HasValue method but this method has been defined to accepts a type of object: public void HasValue(object value); Therefore, if for example we pass a value of type int to it then Code First not only use our desired values (i.e. 1 & 2) in the discriminator column but also changes the column type to be (INT, NOT NULL): modelBuilder.Entity<BillingDetail>()             .Map<BankAccount>(m => m.Requires("BillingDetailType").HasValue(1))             .Map<CreditCard>(m => m.Requires("BillingDetailType").HasValue(2)); SummaryIn this post we learned about Table per Hierarchy as the default mapping strategy in Code First. The disadvantages of the TPH strategy may be too serious for your design—after all, denormalized schemas can become a major burden in the long run. Your DBA may not like it at all. In the next post, we will learn about Table per Type (TPT) strategy that doesn’t expose you to this problem. References ADO.NET team blog Java Persistence with Hibernate book a { text-decoration: none; } a:visited { color: Blue; } .title { padding-bottom: 5px; font-family: Segoe UI; font-size: 11pt; font-weight: bold; padding-top: 15px; } .code, .typeName { font-family: consolas; } .typeName { color: #2b91af; } .padTop5 { padding-top: 5px; } .padTop10 { padding-top: 10px; } p.MsoNormal { margin-top: 0in; margin-right: 0in; margin-bottom: 10.0pt; margin-left: 0in; line-height: 115%; font-size: 11.0pt; font-family: "Calibri" , "sans-serif"; }

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  • Using VLOOKUP in Excel

    - by Mark Virtue
    VLOOKUP is one of Excel’s most useful functions, and it’s also one of the least understood.  In this article, we demystify VLOOKUP by way of a real-life example.  We’ll create a usable Invoice Template for a fictitious company. So what is VLOOKUP?  Well, of course it’s an Excel function.  This article will assume that the reader already has a passing understanding of Excel functions, and can use basic functions such as SUM, AVERAGE, and TODAY.  In its most common usage, VLOOKUP is a database function, meaning that it works with database tables – or more simply, lists of things in an Excel worksheet.  What sort of things?   Well, any sort of thing.  You may have a worksheet that contains a list of employees, or products, or customers, or CDs in your CD collection, or stars in the night sky.  It doesn’t really matter. Here’s an example of a list, or database.  In this case it’s a list of products that our fictitious company sells: Usually lists like this have some sort of unique identifier for each item in the list.  In this case, the unique identifier is in the “Item Code” column.  Note:  For the VLOOKUP function to work with a database/list, that list must have a column containing the unique identifier (or “key”, or “ID”), and that column must be the first column in the table.  Our sample database above satisfies this criterion. The hardest part of using VLOOKUP is understanding exactly what it’s for.  So let’s see if we can get that clear first: VLOOKUP retrieves information from a database/list based on a supplied instance of the unique identifier. Put another way, if you put the VLOOKUP function into a cell and pass it one of the unique identifiers from your database, it will return you one of the pieces of information associated with that unique identifier.  In the example above, you would pass VLOOKUP an item code, and it would return to you either the corresponding item’s description, its price, or its availability (its “In stock” quantity).  Which of these pieces of information will it pass you back?  Well, you get to decide this when you’re creating the formula. If all you need is one piece of information from the database, it would be a lot of trouble to go to to construct a formula with a VLOOKUP function in it.  Typically you would use this sort of functionality in a reusable spreadsheet, such as a template.  Each time someone enters a valid item code, the system would retrieve all the necessary information about the corresponding item. Let’s create an example of this:  An Invoice Template that we can reuse over and over in our fictitious company. First we start Excel… …and we create ourselves a blank invoice: This is how it’s going to work:  The person using the invoice template will fill in a series of item codes in column “A”, and the system will retrieve each item’s description and price, which will be used to calculate the line total for each item (assuming we enter a valid quantity). For the purposes of keeping this example simple, we will locate the product database on a separate sheet in the same workbook: In reality, it’s more likely that the product database would be located in a separate workbook.  It makes little difference to the VLOOKUP function, which doesn’t really care if the database is located on the same sheet, a different sheet, or a completely different workbook. In order to test the VLOOKUP formula we’re about to write, we first enter a valid item code into cell A11: Next, we move the active cell to the cell in which we want information retrieved from the database by VLOOKUP to be stored.  Interestingly, this is the step that most people get wrong.  To explain further:  We are about to create a VLOOKUP formula that will retrieve the description that corresponds to the item code in cell A11.  Where do we want this description put when we get it?  In cell B11, of course.  So that’s where we write the VLOOKUP formula – in cell B11. Select cell B11: We need to locate the list of all available functions that Excel has to offer, so that we can choose VLOOKUP and get some assistance in completing the formula.  This is found by first clicking the Formulas tab, and then clicking Insert Function:   A box appears that allows us to select any of the functions available in Excel.  To find the one we’re looking for, we could type a search term like “lookup” (because the function we’re interested in is a lookup function).  The system would return us a list of all lookup-related functions in Excel.  VLOOKUP is the second one in the list.  Select it an click OK… The Function Arguments box appears, prompting us for all the arguments (or parameters) needed in order to complete the VLOOKUP function.  You can think of this box as the function is asking us the following questions: What unique identifier are you looking up in the database? Where is the database? Which piece of information from the database, associated with the unique identifier, do you wish to have retrieved for you? The first three arguments are shown in bold, indicating that they are mandatory arguments (the VLOOKUP function is incomplete without them and will not return a valid value).  The fourth argument is not bold, meaning that it’s optional:   We will complete the arguments in order, top to bottom. The first argument we need to complete is the Lookup_value argument.  The function needs us to tell it where to find the unique identifier (the item code in this case) that it should be retuning the description of.  We must select the item code we entered earlier (in A11). Click on the selector icon to the right of the first argument: Then click once on the cell containing the item code (A11), and press Enter: The value of “A11” is inserted into the first argument. Now we need to enter a value for the Table_array argument.  In other words, we need to tell VLOOKUP where to find the database/list.  Click on the selector icon next to the second argument: Now locate the database/list and select the entire list – not including the header line.  The database is located on a separate worksheet, so we first click on that worksheet tab: Next we select the entire database, not including the header line: …and press Enter.  The range of cells that represents the database (in this case “’Product Database’!A2:D7”) is entered automatically for us into the second argument. Now we need to enter the third argument, Col_index_num.  We use this argument to specify to VLOOKUP which piece of information from the database, associate with our item code in A11, we wish to have returned to us.  In this particular example, we wish to have the item’s description returned to us.  If you look on the database worksheet, you’ll notice that the “Description” column is the second column in the database.  This means that we must enter a value of “2” into the Col_index_num box: It is important to note that that we are not entering a “2” here because the “Description” column is in the B column on that worksheet.  If the database happened to start in column K of the worksheet, we would still enter a “2” in this field. Finally, we need to decide whether to enter a value into the final VLOOKUP argument, Range_lookup.  This argument requires either a true or false value, or it should be left blank.  When using VLOOKUP with databases (as is true 90% of the time), then the way to decide what to put in this argument can be thought of as follows: If the first column of the database (the column that contains the unique identifiers) is sorted alphabetically/numerically in ascending order, then it’s possible to enter a value of true into this argument, or leave it blank. If the first column of the database is not sorted, or it’s sorted in descending order, then you must enter a value of false into this argument As the first column of our database is not sorted, we enter false into this argument: That’s it!  We’ve entered all the information required for VLOOKUP to return the value we need.  Click the OK button and notice that the description corresponding to item code “R99245” has been correctly entered into cell B11: The formula that was created for us looks like this: If we enter a different item code into cell A11, we will begin to see the power of the VLOOKUP function:  The description cell changes to match the new item code: We can perform a similar set of steps to get the item’s price returned into cell E11.  Note that the new formula must be created in cell E11.  The result will look like this: …and the formula will look like this: Note that the only difference between the two formulae is the third argument (Col_index_num) has changed from a “2” to a “3” (because we want data retrieved from the 3rd column in the database). If we decided to buy 2 of these items, we would enter a “2” into cell D11.  We would then enter a simple formula into cell F11 to get the line total: =D11*E11 …which looks like this… Completing the Invoice Template We’ve learned a lot about VLOOKUP so far.  In fact, we’ve learned all we’re going to learn in this article.  It’s important to note that VLOOKUP can be used in other circumstances besides databases.  This is less common, and may be covered in future How-To Geek articles. Our invoice template is not yet complete.  In order to complete it, we would do the following: We would remove the sample item code from cell A11 and the “2” from cell D11.  This will cause our newly created VLOOKUP formulae to display error messages: We can remedy this by judicious use of Excel’s IF() and ISBLANK() functions.  We change our formula from this…       =VLOOKUP(A11,’Product Database’!A2:D7,2,FALSE) …to this…       =IF(ISBLANK(A11),”",VLOOKUP(A11,’Product Database’!A2:D7,2,FALSE)) We would copy the formulas in cells B11, E11 and F11 down to the remainder of the item rows of the invoice.  Note that if we do this, the resulting formulas will no longer correctly refer to the database table.  We could fix this by changing the cell references for the database to absolute cell references.  Alternatively – and even better – we could create a range name for the entire product database (such as “Products”), and use this range name instead of the cell references.  The formula would change from this…       =IF(ISBLANK(A11),”",VLOOKUP(A11,’Product Database’!A2:D7,2,FALSE)) …to this…       =IF(ISBLANK(A11),”",VLOOKUP(A11,Products,2,FALSE)) …and then copy the formulas down to the rest of the invoice item rows. We would probably “lock” the cells that contain our formulae (or rather unlock the other cells), and then protect the worksheet, in order to ensure that our carefully constructed formulae are not accidentally overwritten when someone comes to fill in the invoice. We would save the file as a template, so that it could be reused by everyone in our company If we were feeling really clever, we would create a database of all our customers in another worksheet, and then use the customer ID entered in cell F5 to automatically fill in the customer’s name and address in cells B6, B7 and B8. If you would like to practice with VLOOKUP, or simply see our resulting Invoice Template, it can be downloaded from here. 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  • How to HitTest in a WPF Grid Panel to find column index.

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    Hi. We need to create a "timeline" feature where a user is allowed to drag and draw "time spans" into a WPF grid (we thought this better than a Canvas since it has resizing capabilities). Each span spans multiple columns, but only one row. We utilize the PreviewMouseDown/Up/Move events to see when the user clicks, drags, and releases the mouse. On the "Down" we create a new rectangle and on the "Move" we resize the rectangle, settings its ColumnSpan property to the correct value every time the mouse enteres the next column. At this point the grid has 48 1-star-sized columns. How do we find out which column the user has clicked on? Right now we are unable to find the column using the VisualTreeHelper.HitTest function. We would like to position the rectangle correctly via Grid.SetColumn(rect, X) and then resize it as needed using Grid.SetColumnSpan(rect, Y) Has anyone done something like this before and can help us? Or, is there a better way to draw what we need? Thanks.

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