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• which is better, creating a view or a new table?

  - by Carson

  I have some demanding mysql queries that are needed to grap same datasets from several mysql tables. I am thinking of creating a table or view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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• How to Audit Database Activity without Performance and Scalability Issues?

  - by GotoError

  I have a need to do auditing all database activity regardless of whether it came from application or someone issuing some sql via other means. So the auditing must be done at the database level. The database in question is Oracle. I looked at doing it via Triggers and also via something called Fine Grained Auditing that Oracle provides. In both cases, we turned on auditing on specific tables and specific columns. However, we found that Performance really sucks when we use either of these methods. Since auditing is an absolute must due to regulations placed around data privacy, I am wondering what is best way to do this without significant performance degradations. If someone has Oracle specific experience with this, it will be helpful but if not just general practices around database activity auditing will be okay as well.

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• How do I pass references as method parameters across AppDomains?

  - by Thiado de Arruda

  I have been trying to get the following code to work(everything is defined in the same assembly) : namespace SomeApp{ public class A : MarshalByRefObject { public byte[] GetSomeData() { // } } public class B : MarshalByRefObject { private A remoteObj; public void SetA(A remoteObj) { this.remoteObj = remoteObj; } } public class C { A someA = new A(); public void Init() { AppDomain domain = AppDomain.CreateDomain("ChildDomain"); string currentAssemblyPath = Assembly.GetExecutingAssembly().Location; B remoteB = domain.domain.CreateInstanceFromAndUnwrap(currentAssemblyPath,"SomeApp.B") as B; remoteB.SetA(someA); // this throws an ArgumentException "Object type cannot be converted to target type." } } } What I'm trying to do is pass a reference of an 'A' instance created in the first AppDomain to the child domain and have the child domain execute a method on the first domain. In some point on 'B' code I'm going to call 'remoteObj.GetSomeData()'. This has to be done because the 'byte[]' from 'GetSomeData' method must be 'calculated' on the first appdomain. What should I do to avoid the exception, or what can I do to achieve the same result?

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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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• ggplot: showing % instead of counts in charts of categorical variables

  - by wishihadabettername

  I'm plotting a categorical variable and instead of showing the counts for each category value, I'm looking for a way to get ggplot to display the percentage of values in that category. Of course, it is possible to create another variable with the calculated percentage and plot that one, but I have to do it several dozens of times and I hope to achieve that in one command. I was experimenting with something like qplot (mydataf) + stat_bin(aes(n=nrow(mydataf), y=..count../n)) + scale_y_continuous(formatter="percent") but I must be using it incorrectly, as I got errors. To easily reproduce the setup, here's a simplified example: mydata <- c ("aa", "bb", null, "bb", "cc", "aa", "aa", "aa", "ee", null, "cc"); mydataf <- factor(mydata); qplot (mydataf); #this shows the count, I'm looking to see % displayed. In the real case I'll probably use ggplot instead of qplot, but the right way to use stat_bin still eludes me. Thank you. UPDATE: I've also tried these four approaches: ggplot(mydataf, aes(y = (..count..)/sum(..count..))) + scale_y_continuous(formatter = 'percent'); ggplot(mydataf, aes(y = (..count..)/sum(..count..))) + scale_y_continuous(formatter = 'percent') + geom_bar(); ggplot(mydataf, aes(x = levels(mydataf), y = (..count..)/sum(..count..))) + scale_y_continuous(formatter = 'percent'); ggplot(mydataf, aes(x = levels(mydataf), y = (..count..)/sum(..count..))) + scale_y_continuous(formatter = 'percent') + geom_bar(); but all 4 give: Error: ggplot2 doesn't know how to deal with data of class factor The same error appears for the simple case of ggplot (data=mydataf, aes(levels(mydataf))) + geom_bar() so it's clearly something about how ggplot interacts with a single vector. I'm scratching my head, googling for that error gives a single result.

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• Return cell reference as result of if statement with vlookups.

  - by EMJ

  I have two sets of data in excel. One contains a set of data which represents the initial step of a process. The other set of data represents the additional steps which take place after the first step is completed. Each of the data records in the "additional step data" has an id in a column. I need to find the identifying codes of the "additional step data" which correspond with the initial step data records. The problem is that I have to match the data in 4 columns between the two data sets and return the id of the "additional step data". I started by doing a combination of an if and vlookup functions, but I got stuck when I tried to figure out how to get the if statement to reference the id of the matching "additional step data". Basically I am trying to avoid having to search by manually filtering between two sets of data and finding corresponding records. Does anyone have any idea about how to do this?

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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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• Insert consecutive numbers

  - by Markus

  Hi. I have a table A (Acons, A1, A2, A3) in which I should insert information from another table B with columns (B1, B2, B3). The Acons is a column in which should contain some consecutive numbers (it is not an identity and I cannot make it identity). I know xmin - starting the from number the sequence has to be computed. How can I insert the rows into the table A, using a single Insert statement? I tried like the following, but it didn't work: DECLARE @i AS INT; SET @i = xmin; INSERT INTO A(Acons, A1, A2, A3) SELECT @i = (Bcons = (@i + 1)), B1, B2, B3 FROM B Unfortunatelly, the above solution does not work;

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• Breaking up large DataGridView for printing

  - by Hal

  Hey, I've got a single-row, 40 column-long DataGridView that i need to print. Since i can neither print it directly (because A4 sheets won't cut it ;)) nor adjust its width to the width of the page itself (because the headers look terrible), i wanted to break the DataGridView to 4 separate pieces and display 10 columns per row (imagine: column 1 to 10 in the first line, column 11 to 21 four or five lines below, etc...). Is there an easy way to do this? I was leaning towards a more manual approach (using fors), but i'd love to know if there's a more elegant way. Cheers

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• Conditional PIVOT/transform problem

  - by IanC

  Hi folks I have a table with three columns, which we'll call ID1, ID2, and Value. Sample data: ID ID1 Value 1 1 0 1 2 1 1 3 1 1 3 2 1 4 0 1 4 1 1 5 0 1 5 2 2 1 2 Value is limited to 0, 1, or 2. What I need to do is pivot/transform this data into a column-based count of how many times each possible Value appears, grouped by ID, ID1. The output of the above should be: ID ID1 Val0 Val1 Val2 1 1 1 0 0 1 2 0 2 0 1 3 0 1 1 1 4 1 1 0 1 5 1 0 1 2 1 0 0 1 I'm using SQL Server 2008. How do I do this?

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• Rendering field data as a link in Ruby on Rails...

  - by bgadoci

  Ok, I think this is probably an easy question but for the life of my I can't figure it out. I have created a table called ugtags and in that table I have two columns (beyond the basics), 'name' and 'link'. I am trying to allow a user to add a link to a page. Ideally they would enter the link title (name) and the url (link) and in the view it would display the title as a link to the url that was entered in the link column. I there a way to do it by simply affecting the <%= link_to h(ugtag.name) %> code?

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• C# MVVM Calculating Total

  - by LnDCobra

  I need to calculate a trade value based on the selected price and quantity. How can The following is my ViewModel: class ViewModel : ViewModelBase { public Trade Trade { get { return _trade; } set { SetField(ref _trade, value, () => Trade); } } private Trade _trade; public decimal TradeValue { get { return Trade.Amount * Trade.Price; } } } ViewModelBase inherits INotifyPropertyChanged and contains SetField() The Following is the Trade class: public class Trade : INotifyPropertyChaged { public virtual Decimal Amount { get { return _amount; } set { SetField(ref _amount, value, () => Amount); } } private Decimal _amount; public virtual Decimal Price { get { return _price; } set { SetField(ref _price, value, () => Price); } } private Decimal _price; ...... } I know due to the design my TradeValue only gets calculated once (when its first requested) and UI doesn't get updated when amount/price changes. What is the best way of achieving this? Any help greatly appreciated.

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• How to parse mathematical expressions involving parentheses

  - by Rob P.

  Please forgive my title, I really don't know how to phrase it better. This isn't a school assignment or anything, but I realize it's a mostly academic question. But, what I've been struggling to do is parse 'math' text and come up with an answer. For Example - I can figure out how to parse '5 + 5' or '3 * 5' - but I fail when I try to correctly chain operations together. (5 + 5) * 3 It's mostly just bugging me that I can't figure it out. If anyone can point me in a direction, I'd really appreciate it. EDIT Thanks for all of the quick responses. I'm sorry I didn't do a better job of explaining. First - I'm not using regular expressions. I also know there are already libraries available that will take, as a string, a mathematical expression and return the correct value. So, I'm mostly looking at this because, sadly, I don't "get it". Second - What I've tried doing (is probably misguided) but I was counting '(' and ')' and evaluating the deepest items first. In simple examples, this worked; but my code is not pretty and more complicated stuff crashes. When I 'calculated' the lowest level, I was modifying the string. So... (5 + 5) * 3 Would turn into 10 * 3 Which would then evaluate to 30 But it just felt 'wrong'. I hope that helps clarify things. I'll certainly check out the links provided.

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• Subquery vs Traditional join with WHERE clause?

  - by BradC

  When joining to a subset of a table, any reason to prefer one of these formats over the other? Subquery version: SELECT ... FROM Customers AS c INNER JOIN (SELECT * FROM Classification WHERE CustomerType = 'Standard') AS cf ON c.TypeCode = cf.Code INNER JOIN SalesReps s ON cf.SalesRepID = s.SalesRepID vs the WHERE clause at the end: SELECT ... FROM Customers AS c INNER JOIN Classification AS cf ON c.TypeCode = cf.Code INNER JOIN SalesReps AS s ON cf.SalesRepID = s.SalesRepID WHERE cf.CustomerType = 'Standard' The WHERE clause at the end feels more "traditional", but the first is arguably more clear, especially as the joins get increasingly complex. Only other reason I can think of to prefer the second is that the "SELECT *" on the first might be returning columns that aren't used later (In this case, I'd probably only need to return cf.Code and Cf.SalesRepID)

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• How to use SqlDataSource for filling combobox as well as datatable or Dataset

  - by Shantanu Gupta

  I am trying to fetch a column value from a datasource when some value is selected from a dropdownlist on its change event. <asp:DropDownList ID="ddlCityName" runat="server" DataSourceID="dsCity" DataTextField="CityName" DataValueField="CityID" AutoPostBack="True" OnTextChanged="CityName_OnTextChanged"> </asp:DropDownList> <asp:SqlDataSource ID="dsCity" runat="server" ConnectionString="<%$ ConnectionStrings:GmapConnectionString %>" SelectCommand="SELECT * FROM [vcity]" ></asp:SqlDataSource> Here I want to fetch any other column's value that is not binded to a ddlCityName from sqldatasource. I have four columns in datasource i.e. name, id, address, phno. I want to fetch an address of a person who selects some value from ddl.

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• In which document do file specifications belong?

  - by Andrew

  In which document would a file specification belong? Perhaps this file is used as an input to a third-party system. Would it belong in its own document? Or would it be better to put it in the functional or design spec? Or somewhere else? When I say file specification, I mean a description of what format the file is (CSV, fixed width, etc), columns, data types, etc. Also, where should you document how the file is generated? i.e. business rules/algorithms which are used to generate the file.

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• SQL Query, return value from table with no join

  - by jdenomme19

  I'm hoping for an idea on the best way to approach what I'm trying to do. I have a table with a list of transactions. Each transactions has a PostDate in DateTime format. I have another table holding the fiscal period values. This table has the following columns; FiscalYear, FiscalMonth, StartDate, EndDate. I'm trying to write a query that will return all values from my transactions table, along with the FiscalYear and FiscalMonth of the PostDate. So I guess I'm just trying to return the FiscalYear and FiscalMonth values when the PostDate falls between the StartDate and EndDate. I've tried using a Subbuery, but I have little experience with them and kept returning an error message that the subquery was returning more than 1 value. Help would be appreciated SELECT Transactions.PostDate, Transactions.TranKey, Transactions.CustKey, (SELECT FiscalPeriod.FiscPer FROM FiscalPeriod WHERE (Transactions.PostDate > CONVERT(Datetime, FiscalPeriod.StartDate, 102)) AND (Transactions.PostDate < CONVERT(DATETIME, FiscalPeriod.EndDate, 102))) AS FisPer FROM Transactions

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• read text files containing binary data as a single matrix in matlab

  - by user1716595

  I have a text file which contains binary data in the following manner: 00000000000000000000000000000000001011111111111111111111111111111111111111111111111111111111110000000000000000000000000000000 00000000000000000000000000000000000000011111111111111111111111111111111111111111111111000111100000000000000000000000000000000 00000000000000000000000000000000000011111111111111111111111111111111111111111111111111111111100000000000000000000000000000000 00000000000000000000000000000000000111111111111111111111111111111111111111111111111111111111100000000000000000000000000000000 00000000000000000000000000000000000011111111111111111111111111111111111111111111111111111111100000000000000000000000000000000 00000000000000000000000000000000000000011111111111111111111111111111111111111111111111111111100000000000000000000000000000000 00000000000000000000000000000000000000011111111111111111111111111111111111111111111111000111110000000000000000000000000000000 00000000000000000000000000000000000000111111111111111111111111111111111111111111111111111111110000000000000000000000000000000 00000000000000000000000000000000000000000000111111111111111111111111111111111111110000000011100000000000000000000000000000000 00000000000000000000000000000000000000011111111111111111111111111111111111111111111111100111110000000000000000000000000000000 00000000000000000000000000000000000111111111111111111111111111111111111111111111111111110111110000000000000000000000000000000 00000000000000000000000000000000001111111111111111111111111111111111111111111111111111111111100000000000000000000000000000000 00000000000000000000000000000000000000001111111111111111111111111111111111111111111111000011100000000000000000000000000000000 00000000000000000000000000000000000000001111111111111111111111111111111111111111111111000011100000000000000000000000000000000 00000000000000000000000000000000000001111111111111111111111111111111111111111111111111111111000000000000000000000000000000000 00000000000000000000000000000000000000011111111111111111111111111111111111111111111110000011100000000000000000000000000000000 00000000000000000000000000000000000000000000011111111111111111111111111111111111100000000011100000000000000000000000000000000 00000000000000000000000000000000000000111111111111111111111111111111111111111111111111110111100000000000000000000000000000000 Plz note that each 1 or 0 is independent i.e the values are not decimal.I need to find the column wise sum of the file.There are 125 columns in all (here it is jumping onto the next line) and there are 840946 rows. I have tried textread,fscanf and a few other matlab commands but the result is that they all read each row in decimal format and create a 840946*1 array.I want to create a 840946*125 array to compute a column wise sum. Kindly help, Thanks!

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• How do you calculate expanding mean on time series using pandas?

  - by mlo

  How would you create a column(s) in the below pandas DataFrame where the new columns are the expanding mean/median of 'val' for each 'Mod_ID_x'. Imagine this as if were time series data and 'ID' 1-2 was on Day 1 and 'ID' 3-4 was on Day 2. I have tried every way I could think of but just can't seem to get it right. left4 = pd.DataFrame({'ID': [1,2,3,4],'val': [10000, 25000, 20000, 40000],'Mod_ID': [15, 35, 15, 42], 'car': ['ford','honda', 'ford', 'lexus']}) right4 = pd.DataFrame({'ID': [3,1,2,4],'color': ['red', 'green', 'blue', 'grey'], 'wheel': ['4wheel','4wheel', '2wheel', '2wheel'], 'Mod_ID': [15, 15, 35, 42]}) df1 = pd.merge(left4, right4, on='ID').drop('Mod_ID_y', axis=1)

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• Using Rails, how can I set my primary key to not be an integer-typed column?

  - by Rudd Zwolinski

  I'm using Rails migrations to manage a database schema, and I'm creating a simple table where I'd like to use a non-integer value as the primary key (in particular, a string). To abstract away from my problem, let's say there's a table employees where employees are identified by an alphanumeric string, e.g. "134SNW". I've tried creating the table in a migration like this: create_table :employees, {:primary_key => :emp_id} do |t| t.string :emp_id t.string :first_name t.string :last_name end What this gives me is what seems like it completely ignored the line t.string :emp_id and went ahead and made it an integer column. Is there some other way to have rails generate the PRIMARY_KEY constraint (I'm using PostgreSQL) for me, without having to write the SQL in an execute call? NOTE: I know it's not best to use string columns as primary keys, so please no answers just saying to add an integer primary key. I may add one anyway, but this question is still valid.

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• How can I neatly clean my R workspace while preserving certain objects?

  - by briandk

  Suppose I'm messing about with some data by binding vectors together, as I'm wont to do on a lazy sunday afternoon. x <- rnorm(25, mean = 65, sd = 10) y <- rnorm(25, mean = 75, sd = 7) z <- 1:25 dd <- data.frame(mscore = x, vscore = y, caseid = z) I've now got my new dataframe dd, which is wonderful. But there's also still the detritus from my prior slicings and dicings: > ls() [1] "dd" "x" "y" "z" What's a simple way to clean up my workspace if I no longer need my "source" columns, but I want to keep the dataframe? That is, now that I'm done manipulating data I'd like to just have dd and none of the smaller variables that might inadvertently mask further analysis: > ls() [1] "dd" I feel like the solution must be of the form rm(ls[ -(dd) ]) or something, but I can't quite figure out how to say "please clean up everything BUT the following objects."

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• How do I select from a stored procedure in Sybase?

  - by Nick Fortescue

  My DBA has constructed me a stored procedure in a Sybase database, for which I don't have the definition. If I run it, it returns a resultset with a set of columns and values. I would like to SELECT further to reduce the rows in the result set. Is this possible? From this question it seems like I could insert the results into a temporary table, but I'm not sure I've got permissions to do this. Is there any way I can SELECT certain rows, or if not, can someone give me example code for simulating with a temporary table?

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• GWT HTMLTable colaspan feature

  - by Sanjay

  Hello all I am using HTMLTable of import com.google.gwt.user.client.ui.HTMLTable I instantiated it like below: HTMLTable table = new Grid(rows, col); Number of rows and columns are decided by the user input. Now I want to used colspan for the specific rows of the table. One way to this is apply css to the that specific row.But problem with this is that Number of column to span are decided by the user input, i.e It may vary every time. So by using css it is something like making it static. So I want to know the way through which I can do colspan on the rows of the table. and Number of column to span is different every time. Thanks in advance

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• Example of user-defined integrity rule in database systems?

  - by Pavel

  Hey everyone. I'm currently preparing for my exams and would like to know some examples of user-defined integrity rule in database systems. As far as I understand, it means that I can set up certain conditions for the columns and when data is inserted it needs to fulfill these conditions. For example: if I set up a rule that an ID needs to consist of 5 integers ONLY then when I insert a row with ID which is made up of integers and some chars then it won't accept it and return an error. Could someone confirm and give me some opinion on that? Thank you very much in advance!

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• Getting started with MIT Proto

  - by Charles

  MIT Proto lacks a basic getting started guide. How do I find a shell that accepts commands like (def foo...) and proto -n 1000 -l -m ...? http://groups.csail.mit.edu/stpg/proto.html I can run in my bash shell: ./proto -n 1000 -s 0.1 -T -l "(red (gradient (= (mid) 0)))" I can't figure out how to run e.g. channel.proto: (def channel (src dst width) (let* ((d (distance src dst)) (trail (<= (+ (gradient src) (gradient dst)) (+ d 0.01))) ;; float error ;; (trail (= (+ (gradient src) (gradient dst)) d)) ) (dilate trail width))) ;; To see a channel calculated from geometric primitives, run: ;; proto -n 1000 -l -m -s 0.5 "(blue (channel (sense 1) (sense 2) 10))" ;; click on a device and hit 't' to set up the source, then click on ;; another device and hit 'y' to designate the destination. At first ;; every device will be blue, but then it should clear and you should ;; see a thick blue path connecting the two devices you selected. Thanks! P.S. Somebody please tag this mit-proto. I can't.

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