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• MySQL indexes - what are the best practises?

  - by Haroldo

  I've been using indexes on my mysql databases for a while now but never properly learnt about them. Generally I put an index on any fields that i will be searching or selecting using a WHERE clause but sometimes it doesn't seem so black and white. What are the best practises for mysql indexes? example situations/dilemas: If a table has six columns and all of them are searchable, should i index all of them or none of them? . What are the negetive performance impacts of indexing? . If i have a VARCHAR 2500 column which is searchable from parts of my site, should i index it?

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• Copy a Table's data from a Stored Procedure

  - by Niike2

  I am learning how to use SQL and Stored Procedures. I know the syntax is incorrect: Copy data from one table into another table on another Database with a Stored Procedure. The problem is I don't know what table or what database to copy to. I want it to use parameters and not specify the columns specifically. I have 2 Databases (Master_db and Master_copy) and the same table structure on each DB. I want to quickly select a table in Master_db and copy that table's data into Master_copy table with same name. I have come up with something like this: USE Master_DB CREATE PROCEDURE TransferData DEFINE @tableFrom, @tableTo, @databaseTo; INSERT INTO @databaseTo.dbo.@databaseTo SELECT * FROM Master_DB.dbo.@tableFrom GO;

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• I Need Help Fixing My Small Time Sheet Table - Relational DB - SQL Server

  - by user327387

  I have a TimeSheet table as: CREATE TABLE TimeSheet ( timeSheetID employeeID setDate timeIn outToLunch returnFromLunch timeOut ); Employee will set his/her time sheet daily, i want to ensure that he/she doesn't cheat. What should i do? Should i create a column that gets date/time of the system when insertion/update happens to the table and then compare the created date/time with the time employee's specified - If so in this case i will have to create date/time column for timeIn, outToLunch, returnFromLunch and timeOut. I don't know, what do you suggest? Note: i'm concerned about tracking these 4 columns timeIn, outToLunch, returnFromLunch and timeOut

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• Changing the value of datagridComboBoxColumn on checking/unchecking of check boxes in datagridcheckb

  - by MD

  I have a wpf data grid,where there are two data template columns One of which ahs check box as the data template adn teh other has combo box as the data template. Now my requirement is,i need to disable few of the options in the combo boxes depending on the check box checked or unchecked for each individual rows... With the cod etaht i ahve tried,i am able to change teh values of teh combo boxes,but it changes for the whole column and not fro individual rows.. Please let me kneo how to determine the combo boxes for the corresponding check boxes in a particular row.

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• python how to put data on y-axis when plotting histogram

  - by user3041107

  I don't quite understand how to control y - axis when using plt.hist plot in python. I read my .txt data file - it contains 10 columns with various data. If I want to plot distribution of strain on x axis I take column n.5. But what kind of value appears on y axis ??? Don't understand that. here is the code: import numpy import matplotlib.pyplot as plt from pylab import * from scipy.stats import norm import sys strain = [] infile = sys.argv[1] for line in infile: ret = numpy.loadtxt(infile) strain += list(ret[:,5]) fig = plt.figure() plt.hist(strain, bins = 20) plt.show() Thanks for help!

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• Copy new records from datatable and identify changes in old records

  - by Betite

  Assume there are two tables: Remote_table and My_table. Remote_table has 6 columns: **PROJECT JOB_TYPE MONTH YEAR** HOURS IS_DELETED 134393 70 1 2013 30 0 134393 70 2 2013 50 0 134393 70 3 2013 80 0 134393 70 10 2012 10 0 134393 70 11 2012 0 0 134393 70 12 2012 15 0 My_table is a copy of remote_table. I tried to copy only the new records from the remote_table by this query: SELECT * FROM [remote_DB].[LudanProjectManager].[dbo].Remote_table EXCEPT SELECT * FROM My_table It works OK but I get a duplicate primary key exception when changes have been made on the remote_table on the hours column. Can anyone think of a way to copy only the new records from remote_table and if changes has been made on old records, to identify them and update the my_table to correspond?

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• Java. Writing a matrix in a file using column information. ( matrix transposition )

  - by Dmitry

  Hello, everybody! I have a file in which a matrix is stored. This file has a RandomAccessFile type. This matrix is stored by columns. I mean that in an i-th row of this matrix an i-th column (of a real matrix) is stored. There is an example: i-th row: 1 2 3 4 (in the file). That means that the real matrix has an i-th column: (1 2 3 4)(is transposed). I need to save this matrix in a natural way (by rows) in a new file, which I will then open with FileReader and display with TextArea. Do you know, how to do that? If so, please help =)

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• How to prevent CAST errors on SSIS ?

  - by manitra

  Hello, The question Is it possible to ask SSIS to cast a value and return NULL in case the cast is not allowed instead of throwing an error ? My environment I'm using Visual Studio 2005 and Sql Server 2005 on Windows Server 2003. The general context Just in case you're curious, here is my use case. I have to store data coming from somewhere in a generic table (key/value structure with history) witch contains some sort of value that can be strings, numbers or dates. The structure is something like this : table Values { Id int, Date datetime, -- for history Key nvarchar(50) not null, Value nvarchar(50), DateValue datetime, NumberValue numeric(19,9) } I want to put the raw value in the Value column and try to put the same value in the DateValue column when i'm able to cast it to Datetime in the NumberValue column when i'm able to cast it to a number Those two typed columns would make all sort of aggregation and manipulation much easier and faster later. That's it, now you know why i'm asking this strange question. ============ Thanks in advance for your help.

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• T-SQL Getting duplicate rows returned

  - by cBlaine

  The following code section is returning multiple columns for a few records. SELECT a.ClientID,ltrim(rtrim(c.FirstName)) + ' ' + case when c.MiddleName <> '' then ltrim(rtrim(c.MiddleName)) + '. ' else '' end + ltrim(rtrim(c.LastName)) as ClientName, a.MISCode, b.Address, b.City, dbo.ClientGetEnrolledPrograms(CONVERT(int,a.ClientID)) as Abbreviation FROM ClientDetail a JOIN Address b on(a.PersonID = b.PersonID) JOIN Person c on(a.PersonID = c.PersonID) LEFT JOIN ProgramEnrollments d on(d.ClientID = a.ClientID and d.Status = 'Enrolled' and d.HistoricalPKID is null) LEFT JOIN Program e on(d.ProgramID = e.ProgramID and e.HistoricalPKID is null) WHERE a.MichiganWorksData=1 I've isolated the issue to the ProgramEnrollments table. This table holds one-to-many relationships where each ClientID can be enrolled in many programs. So for each program a client is enrolled in, there is a record in the table. The final result set is therefore returning a row for each row in the ProgramEnrollments table based on these joins. I presume my join is the issue but I don't see the problem. Thoughts/Suggestions? Thanks, Chuck

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• Ideas on limiting content to single printed page?

  - by James Skidmore

  I have 5-6 text areas that users fill out in a template (a couple of columns, basically a newsletter format). I'm needing to limit their content to one printed page, but I'm having a hard time coming up with practical solutions. The printed format (margin, font size, etc.) will be the same for all users, as it's printed from a central source. I've had a couple of ideas, but all of them seem rather unreliable and difficult to implement: Determine height of content using JavaScript and estimate the number of printed pages from that. The problem with this is that browser font sizes can vary, it's only a rough estimate (pixels to inches), etc. Limit the number of characters. This is problematic because there are various text fields, certain characters (like M) take up more space than others (like I), and line breaks obviously count for much more. What ideas do you all have? I appreciate your help!

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• How to get out information from a DataGridView?

  - by ghost_j1

  I am working on program that calculate the GPAs for university students in C#. I have made a gridview that contains columns for each subject. Its mark as letter and number. After the user "student" insert his/her subject I want to let the user click a button that will get the mark and the number of the credit hours of each subject. Calculate the GPA for the student and put the result in a textbox. I am having trouble getting started. Any advice for a good place to start?

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• ASP.NET GridView - how to enable validation declaratively

  - by Joe

  It it possible to enable validation in an ASP.NET GridView purely declaratively? What I've tried: A GridView bound to an ObjectDataSource with SelectMethod and UpdateMethod defined The GridView contains some ReadOnly BoundField columns and a TemplateField whose EditTemplate contains a TextBox and a RegularExpressionValidator that only allows numeric input in the TextBox. The GridView also contains a CommandField with ShowEditButton=true and CausesValidation=true. If I click on Edit, enter an invalid value, then click on Save, there is a PostBack, and an exception is thrown in the server (Input string was not in a correct format). I can of course avoid this by adding validation code to the RowUpdating event handler on the server (see below), but is there any declarative way to force the validation to be done without adding this code? protected void MyGridView_RowUpdating(object sender, GridViewUpdateEventArgs e) { Page.Validate("MyValidationGroup"); if (!Page.IsValid) { e.Cancel = true; } }

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• Best .NET Solution for Frequently Changed Database

  - by sestocker

  I am currently architecting a small CRUD applicaton. Their database is a huge mess and will be changing frequently over the course of the next 6 months to a year. What would you recommend for my data layer: 1) ORM (if so, which one?) 2) Linq2Sql 3) Stored Procedures 4) Parametrized Queries I really need a solution that will be dynamic enough (both fast and easy) where I can replace tables and add/delete columns frequently. Note: I do not have much experience with ORM (only a little SubSonic) and generally tend to use stored procedures so maybe that would be the way to go. I would love to learn Ling2Sql or NHibernate if either would allow for the situation I've described above.

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• Automatically Add a Prefix to Column Names for @Embeddable Classes

  - by VeeArr

  I am developing a project in which I am persisting some POJOs by adding Hibernate annotations. One problem I am running into is that code like this fails, as Hibernate tries to map the sub-fields within the Time_T onto the same column (i.e. startTime.sec and stopTime.sec both try to map to the colum sec, causing an error). @Entity public class ExampleClass { @Id long eventId; Time_T startTime; Time_T stopTime; } @Embeddable public class Time_T { int sec; int nsec; } As there will be many occurrences like this throughout the system, it would be nice if there was an option to automatically append a prefix to the column name (e.g. make the columns be startTime_sec, startTime_nsec, stopTime_sec, stopTime_nsec), without having to apply overrides on a per-field basis. Does Hibernate have this capability, or is there any other reasonable work-around?

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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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• Can I force MySQL to output results before query is completed?

  - by Gordon Royle

  I have a large MySQL table (about 750 million rows) and I just want to extract a couple of columns. SELECT id, delid FROM tbl_name; No joins or selection criteria or anything. There is an index on both fields (separately). In principle, it could just start reading the table and spitting out the values immediately, but in practice the whole system just chews up memory and basically grinds to a halt. It seems like the entire query is being executed and the output stored somewhere before ANY output is produced... I've searched on unbuffering, turning off caches etc, but just cannot find the answer. (mysqldump is almost what I want except it dumps the whole table - but at least it just starts producing output immediately)

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• Store the day of the week and time

  - by bsiddiqui

  I have a two part question about storing day(s) of the week and time in a database. I'm using Rails 4.0, ruby 2.0.0, and postgres. I have certain events and those events have a schedule. For the event Skydiving for example, for example, I might have Tuesday and Wednesday and 3 pm. 1) Is there a way for me to store the the record for Tuesday and Wednesday in one row or do should I have two records? 2) What is the best way to store the day and time? Is there a way to store day of week and time (not datetime) or should these be separate columns? If they should be separate, how would you store day of week? I was thinking of storing them as integer values (0 for Sunday, 1 for Monday, etc) since that's how wday method for the Time class does it. Any suggestions would be super helpful. Thanks!

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• Sum of distinc rows after a 1-many table join

  - by Lock

  I have 2 tables that I am joining. Table 1 has 1-many relationship with table 2. That is, table 2 can return multiple rows for a single row of table 1. Because of this, the records of table 1 is duplicated for as many rows as are on table 2.. which is expected. Now, I have a sum on one of the columns from table 1, but because of the multiple rows that get returned on the join, the sum is obviously multiplying. Is there a way to get this number back to its original number? I tried dividing by the count of rows from table 2 but this didnt quite give me the expected result. Are there any analytical functions that could do this? I almost want something like "if this row has not yet been counted in the sum, add it to the sum"

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• Reasons for sticking with TEXT, NTEXT and IMAGE instead of (N)VARCHAR(max) and VARBINARY(max)

  - by John Assymptoth

  TEXT, NTEXT and IMAGE have been deprecated a long time ago and will, eventually, be removed from SQL Server. However, they are not going to be discontinued right away, not even in the next version of SQL Server, so it's not convenient for my enterprise to transform thousands of columns right away, even if it is using SQL Server 2012. What arguments can I use to postpone this migration? I know there are some advantages in using the new types. But I'm strictly looking for reasons not to migrate my data that is already functioning pretty well in the old types.

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• How can I efficiently retrieve a large number of database settings as PHP variables?

  - by Steven

  Currently all of my script's settings are located in a PHP file which I 'include'. I'm in the process of moving these settings (about 100) to a database table called 'settings'. However I'm struggling to find an efficient way of retrieving all of them into the file. The settings table has 3 columns: ID (autoincrements) name value Two example rows might be: 1 admin_user john 2 admin_email_address [email protected] The only way I can think of retrieving each setting is like this: $result = mysql_query("SELECT value FROM settings WHERE name = 'admin_user'"); $row = mysql_fetch_array($result); $admin_user = $row['value']; $result = mysql_query("SELECT value FROM settings WHERE name = 'admin_email_address'"); $row = mysql_fetch_array($result); $admin_email_address = $row['value']; etc etc Doing it this way will take up a lot of code and will likely be slow. Is there a better way? Thanks.

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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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• how do I integrate the aspnet_users table (asp.net membership) into my existing database

  - by ooo

  i have a database that already has a users table COLUMNS: userID - int loginName - string First - string Last - string i just installed the asp.net membership table. Right now all of my tables are joined into my users table foreign keyed into the "userId" field How do i integrate asp.net_users table into my schema? here are the ideas i thought of: Add a membership_id field to my users table and on new inserts, include that new field in my users table. This seems like the cleanest way as i dont need to break any existing relationships. break all existing relationship and move all of the fields in my user table into the asp.net_users table. This seems like a pain but ultimately will lead to the most simple, normalized solution any thoughts?

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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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• Database migration

  - by graham.reeds

  We are migrating a client's own database schema to our own (both SQL-Server). Most of the mappings from their schema to ours have been indentified and rules been agreed on if the columns don't exactly align (default values etc.) Previously, depending on who was assigned the task, this has been done either with a mixture of sql scripts or one-off vb apps. I was thinking there must be a application (commercial or otherwise) where you can assign these mappings/rules and have it stream the data across. Surely the setting up and configuration of this tool would be less than the creation of ad-hoc scripts... Is there an app? Apart from the obvious 'be careful' any tips to mitigate the stress of a non-DBA porting one schema to another?

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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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