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  • How to write this Link2Sql select query

    - by RememberME
    I have 3 tables: subcontracts, companies and contacts. Each table has a active_status flags which shows that the item is still active (hasn't been deleted). Each contact has a company_id field which stores the id of the contact's company. Each subcontract has a company_id field which stores the subcontract's company. Each company has a company_id field which holds its guid and a primary_company field, b/c the company could be a subsidiary. If it's a subsidiary, the primary_company field holds the id of the primary company. I have a subcontract form. On the form, I have a drop-down of contacts which are stored in a contact table. Currently the drop-down lists all contacts. I would like to have the drop-down only list contacts which belong to the subcontract's company or any of that company's subsidiaries. I have the following query which I use elsewhere in the program to pass a company_id and get its subsidiaries. public IQueryable<company> GetSubsidiaryCompanies(Guid id) { return from c in db.companies where c.primary_company == id && c.active_status == true select c; } This is my current contact selection public IQueryable<contact> GetContacts() { return from c in db.contacts where c.active_status == true orderby c.contact_name select c; } What I need to do is pass it the subcontract.company_id and then only return the contacts where contact.company_id == subcontract.company_id or contact.company_id == one of the subsidiary ids.

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  • Fast way to code forms in C# which is bind to SQL data

    - by adopilot
    I am coming from MS-ACESS world and their programing habits, There was nice utility to make form from table, You can simply hit right click on table and make form for it. Now I looking for something similar for Visual Studio and WinForms. I am trying to develop simple application for which I need to have more then 30 forms for handling data, till now I designed database tables, keys and sprocs in SQL2008 and before I start coding forms for handling data, I asking You for main guidelines how to save my time while coding forms.

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  • Error invoking stored procedure with input parameter from ADO.Net

    - by George2
    Hello everyone, I am using VSTS 2008 + C# + .Net 3.5 + ADO.Net. Here is my code and related error message. The error message says, @Param1 is not supplied, but actually it is supplied in my code. Any ideas what is wrong? System.Data.SqlClient.SqlException: Procedure or function 'Pr_Foo' expects parameter '@Param1', which was not supplied. class Program { private static SqlCommand _command; private static SqlConnection connection; private static readonly string _storedProcedureName = "Pr_Foo"; private static readonly string connectionString = "server=.;integrated Security=sspi;initial catalog=FooDB"; public static void Prepare() { connection = new SqlConnection(connectionString); connection.Open(); _command = connection.CreateCommand(); _command.CommandText = _storedProcedureName; _command.CommandType = CommandType.StoredProcedure; } public static void Dispose() { connection.Close(); } public static void Run() { try { SqlParameter Param1 = _command.Parameters.Add("@Param1", SqlDbType.Int, 300101); Param1.Direction = ParameterDirection.Input; SqlParameter Param2 = _command.Parameters.Add("@Param2", SqlDbType.Int, 100); portal_SiteInfoID.Direction = ParameterDirection.Input; SqlParameter Param3 = _command.Parameters.Add("@Param3", SqlDbType.Int, 200); portal_RoleInfoID.Direction = ParameterDirection.Input; _command.ExecuteScalar(); } catch (Exception e) { Console.WriteLine(e); } } static void Main(string[] args) { try { Prepare(); Thread t1 = new Thread(Program.Run); t1.Start(); t1.Join(); Dispose(); } catch (Exception ex) { Console.WriteLine(ex.Message + "\t" + ex.StackTrace); } } } Thanks in advance, George

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  • mysql query for getting all messages that belong to user's contacts

    - by aharon
    So I have a database that is setup sort of like this (simplified, and in terms of the tables, all are InnoDBs): Users: contains based user authentication information (uid, username, encrypted password, et cetera) Contacts: contains two rows per relationship that exists between users as (uid1, uid2), (uid2, uid1) to allow for a good 1:1 relationship (must be mutual) between users Messages: has messages that consist of a blob, owner-id, message-id (auto_increment) So my question is, what's the best MySQL query to get all messages that belong to all the contacts of a specific user? Is there an efficient way to do this?

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  • Why would I do an inner join on a non-distinct field?

    - by froadie
    I just came across a query that does an inner join on a non-distinct field. I've never seen this before and I'm a little confused about this usage. Something like: SELECT distinct all, my, stuff FROM myTable INNER JOIN myOtherTable ON myTable.nonDistinctField = myOtherTable.nonDistinctField (WHERE some filters here...) I'm not quite sure what my question is or how to phrase it, or why exactly this confuses me, but I was wondering if anyone could explain why someone would need to do an inner join on a non-distinct field and then select only distinct values...? Is there ever a legitimate use of an inner join on a non-distinct field? What would be the purpose? And if there's is a legitimate reason for such a query, can you give examples of where it would be used?

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  • SQL query to get latest record for all distinct items in a table

    - by David Buckley
    I have a table of all sales defined like: mysql> describe saledata; +-------------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------------------+------+-----+---------+-------+ | SaleDate | datetime | NO | | NULL | | | StoreID | bigint(20) unsigned | NO | | NULL | | | Quantity | int(10) unsigned | NO | | NULL | | | Price | decimal(19,4) | NO | | NULL | | | ItemID | bigint(20) unsigned | NO | | NULL | | +-------------------+---------------------+------+-----+---------+-------+ I need to get the last sale price for all items (as the price may change). I know I can run a query like: SELECT price FROM saledata WHERE itemID = 1234 AND storeID = 111 ORDER BY saledate DESC LIMIT 1 However, I want to be able to get the last sale price for all items (the ItemIDs are stored in a separate item table) and insert them into a separate table. How can I get this data? I've tried queries like this: SELECT storeID, itemID, price FROM saledata WHERE itemID IN (SELECT itemID from itemmap) ORDER BY saledate DESC LIMIT 1 and then wrap that into an insert, but it's not getting the proper data. Is there one query I can run to get the last price for each item and insert that into a table defined like: mysql> describe lastsale; +-------------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------------------+------+-----+---------+-------+ | StoreID | bigint(20) unsigned | NO | | NULL | | | Price | decimal(19,4) | NO | | NULL | | | ItemID | bigint(20) unsigned | NO | | NULL | | +-------------------+---------------------+------+-----+---------+-------+

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  • Can't find which row is causing conversion error

    - by Marwan
    I have the following table: CREATE TABLE [dbo].[Accounts1]( [AccountId] [nvarchar](50) NULL, [ExpiryDate] [nvarchar](50) NULL ) I am trying to convert nvarchar to datetime using this query: select convert(datetime, expirydate) from accounts I get this error: Conversion failed when converting datetime from character string. The status bar says "2390 rows". I go to rows 2390, 2391 and 2392. There is nothing wrong with the data there. I even try to convert those particular rows and it works. How can I find out which row(s) is causing the conversion error?

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  • How To Find Reasons of Why Site Goes Online/Offline

    - by HollerTrain
    Seems today a website I manage has been going online and offline throughout the entire day. I have no idea what is causing the issue so I am seeking guidance on where to start. It is a Wordpress based site. So here is what I DO know: I use a program that pings the server every minute and when the server is not responding me it emails me, so I can know exactly when the site is online and offline. The site between 8pm to 12pm 12.28, and around the 1a hour early morning 12.29 (New York City timezone, and all times below are in same timezone). At the time of the ups/downs I see a lot of strain on the memory usage. Look at the load average when the site is going online/offline (http://screencast.com/t/BRlfXkqrbJII). Then I ran this command to restart http (http://screencast.com/t/usVtYWZ2Qi) and the memory usage then goes down to this (http://screencast.com/t/VdTIy3bgZiQB). An hour after I restarted http, the site then went offline/online so restarting the http didn't do much help. When the site is going offline/online, I ran the top command and get this (http://screencast.com/t/zEwr7YQj3). Here is a top command when the site is at it's lowest (http://screencast.com/t/eaMfha9lbT - so this would be dubbged "normal"). Here is a bandwidth report (http://screencast.com/t/AS0h2CH1Gypq). The traffic doesn't seem to be that much (http://screencast.com/t/s7hrWNNic1K), but looking at my times the site is going up/down this may be one of the reasons? I have the dvp Nitro package at Media Temple (http://mediatemple.net/webhosting/nitro/). So at this point I would request some help in trying to figure out what the cause of this is, and how I can go about pinpointing this issue. ANY HELP is greatly appreciated.

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  • Insert rownumber repeatedly in records in t-sql.

    - by jeff
    Hi, I want to insert a row number in a records like counting rows in a specific number of range. example output: RowNumber ID Name 1 20 a 2 21 b 3 22 c 1 23 d 2 24 e 3 25 f 1 26 g 2 27 h 3 28 i 1 29 j 2 30 k I rather to try using the rownumber() over (partition by order by column name) but my real records are not containing columns that will count into 1-3 rownumber. I already try to loop each of record to insert a row count 1-3 but this loop affects the performance of the query. The query will use for the RDL report, that is why as much as possible the performance of the query must be good. any suggestions are welcome. Thanks

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  • Using PHP variables inside SQL statements?

    - by Homer
    For some reason I can't pass a var inside a mysql statement. I have a function that can be used for multiple tables. So instead of repeating the code I want to change the table that is selected from like so, function show_all_records($table_name) { mysql_query("SELECT * FROM $table_name"); etc, etc... } And to call the function I use show_all_records("some_table") or show_all_records("some_other_table") depending on which table I want to select from at the moment. But it's not working, is this because variables can't be passed through mysql statements?

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  • comparing data via a function

    - by tigermain
    I have two sets of data (locations) in seperate tables and I need to compare if they match or not. I have a UDF which performs a calculation based upon 5 values from each table. How do I perform a select with a join using this udf? my udf is basically defined by.... ALTER FUNCTION [dbo].[MatchRanking] ( @Latitude FLOAT , @Longitude FLOAT , @Postcode VARCHAR(16) , @CompanyName VARCHAR(256) , @TelephoneNumber VARCHAR(32) , @Latitude2 FLOAT , @Longitude2 FLOAT , @Postcode2 VARCHAR(16) , @CompanyName2 VARCHAR(256) , @TelephoneNumber2 VARCHAR(32) ) RETURNS INT

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  • Can I serialize an object if I didn't write the class used to instantiate that object?

    - by Richard77
    Hello, I've a simple class [Serializable] public class MyClass { public String FirstName { get; set: } public String LastName { get; set: } //Bellow is what I would like to do //But, it's not working //I get an exception ContactDataContext db = new ContactDataContext(); public void Save() { Contact contact = new Contact(); contact.FirstName = FirstName; contact.LastName = LastName; db.Contacts.InsertOnSubmit(contact); db.SubmitChanges(); } } I wanted to attach a Save method to the class so that I could call it on each object. When I introduced the above statement which contains ContactDataContext, I got the following error "In assembly ... PublicKeyToken=null' is not marked as serializable" It's clear that the DataContext class is generated by the framework (). I checked and did not see where that class was marked serialize. What can I do to overcome that? What's the rule when I'm not the author of a class? Just go ahead and mark the DataContext class as serializable, and pretend that everything will work? Thanks for helping

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  • php using wamp server start up error

    - by mathirengasamy
    i try to install moodle web software...i m using wamp server and sqlserver 2005 version. i install php driver for php5.3.0 thread safe version..i just paste that php_sqlsrv_ts.dll driver file into my php ext directory...i include this line extension=php_sqlsrv_ts.dll in my php.ini file... now i restart my wampserver...i m getting this error... PHP Startup: sqlsrv: Unable to initialize module Module compiled with module API=20060613 PHP compiled with module API=20090626 These options need to match get this error also in my apache log file ADODB Error: [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified please anybody help me..

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  • Two different tables or just one with bool column?

    - by Aidas
    We have two tables: OriginalDocument and ProcessedDocument. In the first one we put an original, not processed document. After it's validated and processed (converted to our xml format and parsed), it's put into Document table. Processed document can be valid or invalid. Which makes more sense: have two different tables for valid and invalid documents or just have one with 'Valid' column? Some of the columns (~5-7) are irrelevant for invalid document. Storing both invalid and valid documents would also make Document table filled with 'NULL' columns (if document is invalid, information like document number, receiver can be unknown). What else should we consider and weigh, when making this decision?

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  • Linq2SQL vs NHibernate performance (have I gone mad?)

    - by HeavyWave
    I have written the following tests to compare performance of Linq2SQL and NHibernate and I find results to be somewhat strange. Mappings are straight forward and identical for both. Both are running against a live DB. Although I'm not deleting Campaigns in case of Linq, but that shouldn't affect performance by more than 10 ms. Linq: [Test] public void Test1000ReadsWritesToAgentStateLinqPrecompiled() { Stopwatch sw = new Stopwatch(); Stopwatch swIn = new Stopwatch(); sw.Start(); for (int i = 0; i < 1000; i++) { swIn.Reset(); swIn.Start(); ReadWriteAndDeleteAgentStateWithLinqPrecompiled(); swIn.Stop(); Console.WriteLine("Run ReadWriteAndDeleteAgentState: " + swIn.ElapsedMilliseconds + " ms"); } sw.Stop(); Console.WriteLine("Total Time: " + sw.ElapsedMilliseconds + " ms"); Console.WriteLine("Average time to execute queries: " + sw.ElapsedMilliseconds / 1000 + " ms"); } private static readonly Func<AgentDesktop3DataContext, int, EntityModel.CampaignDetail> GetCampaignById = CompiledQuery.Compile<AgentDesktop3DataContext, int, EntityModel.CampaignDetail>( (ctx, sessionId) => (from cd in ctx.CampaignDetails join a in ctx.AgentCampaigns on cd.CampaignDetailId equals a.CampaignDetailId where a.AgentStateId == sessionId select cd).FirstOrDefault()); private void ReadWriteAndDeleteAgentStateWithLinqPrecompiled() { int id = 0; using (var ctx = new AgentDesktop3DataContext()) { EntityModel.AgentState agentState = new EntityModel.AgentState(); var campaign = new EntityModel.CampaignDetail { CampaignName = "Test" }; var campaignDisposition = new EntityModel.CampaignDisposition { Code = "123" }; campaignDisposition.Description = "abc"; campaign.CampaignDispositions.Add(campaignDisposition); agentState.CallState = 3; campaign.AgentCampaigns.Add(new AgentCampaign { AgentState = agentState }); ctx.CampaignDetails.InsertOnSubmit(campaign); ctx.AgentStates.InsertOnSubmit(agentState); ctx.SubmitChanges(); id = agentState.AgentStateId; } using (var ctx = new AgentDesktop3DataContext()) { var dbAgentState = ctx.GetAgentStateById(id); Assert.IsNotNull(dbAgentState); Assert.AreEqual(dbAgentState.CallState, 3); var campaignDetails = GetCampaignById(ctx, id); Assert.AreEqual(campaignDetails.CampaignDispositions[0].Description, "abc"); } using (var ctx = new AgentDesktop3DataContext()) { ctx.DeleteSessionById(id); } } NHibernate (the loop is the same): private void ReadWriteAndDeleteAgentState() { var id = WriteAgentState().Id; StartNewTransaction(); var dbAgentState = agentStateRepository.Get(id); Assert.IsNotNull(dbAgentState); Assert.AreEqual(dbAgentState.CallState, 3); Assert.AreEqual(dbAgentState.Campaigns[0].Dispositions[0].Description, "abc"); var campaignId = dbAgentState.Campaigns[0].Id; agentStateRepository.Delete(dbAgentState); NHibernateSession.Current.Transaction.Commit(); Cleanup(campaignId); NHibernateSession.Current.BeginTransaction(); } Results: NHibernate: Total Time: 9469 ms Average time to execute 13 queries: 9 ms Linq: Total Time: 127200 ms Average time to execute 13 queries: 127 ms Linq lost by 13.5 times! Event with precompiled queries (both read queries are precompiled). This can't be right, although I expected NHibernate to be faster, this is just too big of a difference, considering mappings are identical and NHibernate actually executes more queries against the DB.

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  • Should I include user_id in multiple tables?

    - by Drarok
    I'm at the planning stages of a multi-user application where each user will only have access their own data. There'll be a few tables that relate to each other, so I could use JOINs to ensure they're accessing only their data, but should I include user_id in each table? Would this be faster? It would certainly make some of the queries easier in the long run. Thanks!

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  • Help on understanding multiple columns on an index?

    - by Xaisoft
    Assume I have a table called "table" and I have 3 columns, a, b, and c. What does it mean to have a non-clustered index on columns a,b? Is a nonclustered index on columns a,b the same as a nonclustered index on columns b,a? (Note the order). Also, Is a nonclustered index on column a the same as a nonclustered index on a,c? I was looking at the website sqlserver performance and they had these dmv scripts where it would tell you if you had overlapping indexes and I believe it was saying that having an index on a is the same as a,b, so it is redundant. Is this true about indexes? One last question is why is the clustered index put on the primary key. Most of the time the primary key is not queried against, so shouldn't the clustered index be on the most queried column. I am probably missing something here like having it on the primary key speeds up joins? Great explanations. Should I turn this into a wiki and change the title index explanation?

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  • Stored Procedure in Entity Framework

    - by kamal
    Hi I had added the Stored procedure in my Entity framework and i also imported the functions in the edmx. Is it must to add all the three functions insert, update, and delete functions to a table. I had tried with insert alone and also with all, but why can't i get the name of the stored procedure in the connection string. Let me know what i done clearly. I had added the sp i had imported the functions in the model browser. i had also mapped the insert, update and delete function to the table with return type only for insert and update. Still i can't get the name of SP in the connection string. Please let me know how could i resolve this issue. Thanks in Advance, Kamal.

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  • Should I commit or rollback a transaction that creates a temp table, reads, then deletes it?

    - by Triynko
    To select information related to a list of hundreds of IDs... rather than make a huge select statement, I create temp table, insert the ids into it, join it with a table to select the rows matching the IDs, then delete the temp table. So this is essentially a read operation, with no permanent changes made to any persistent database tables. I do this in a transaction, to ensure the temp table is deleted when I'm finished. My question is... what happens when I commit such a transaction vs. let it roll it back? Performance-wise... does the DB engine have to do more work to roll back the transaction vs committing it? Is there even a difference since the only modifications are done to a temp table? Related question here, but doesn't answer my specific case involving temp tables: http://stackoverflow.com/questions/309834/should-i-commit-or-rollback-a-read-transaction

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  • What resources will help me understand the fundamentals of Relational Database Systems.

    - by Rachel
    This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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  • ASP.NET GridView Sort?

    - by Curtis White
    I'm performing a query with a sort in the Selecting event of the LinqDataSource. I'm then casting my query to a list and assigning it to the result. I'm using this data source in an ASP.NET gridview. I can see the list is sorted but when the ASP.NET gridview does not seem to be respecting the sort order. How can I get the gridview to respect my default sort order?

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  • Bulk inserting and updating with Entity Framework (Probably a better alternative?)

    - by Dave
    I have a data set of devices, addresses, and companies that I need to import into our database, with the catch that our database may already include a specific device/address/company that is included in the new data set. If that is the case, I need to update that entry with the new information in the data set, excluding addresses. We check if an exact copy of that address exists, otherwise we make a new entry. My issue is that it is very slow to attempt to grab a device/company in EF and if it exist updated it, otherwise insert it. To fix this I tried to get all the companies, devices, and addresses and insert them into respective hashmaps, and check if the identifier of the new data exists in the hashmap. This hasn't led to any performance increases. I've included my code below. Typically I would do a batch insert, I'm not sure what I would do for a batch update though. Can someone advise a different route? var context = ObjectContextHelper.CurrentObjectContext; var oldDevices = context.Devices; var companies = context.Companies; var addresses = context.Addresses; Dictionary<string, Company> companyMap = new Dictionary<string, Company>(StringComparer.OrdinalIgnoreCase); Dictionary<string, Device> deviceMap = new Dictionary<string, Device>(StringComparer.OrdinalIgnoreCase); Dictionary<string, Address> addressMap = new Dictionary<string, Address>(StringComparer.OrdinalIgnoreCase); foreach (Company c in companies) { if (c.CompanyAccountID != null && !companyMap.ContainsKey(c.CompanyAccountID)) companyMap.Add(c.CompanyAccountID, c); } foreach (Device d in oldDevices) { if (d.SerialNumber != null && !deviceMap.ContainsKey(d.SerialNumber)) deviceMap.Add(d.SerialNumber, d); } foreach (Address a in addresses) { string identifier = GetAddressIdentifier(a); if (!addressMap.ContainsKey(identifier)) addressMap.Add(identifier, a); } foreach (DeviceData.TabsDevice device in devices) { // update a device Company tempCompany; Address tempAddress; Device currentDevice; if (deviceMap.ContainsKey(device.SerialNumber)) //update a device deviceMap.TryGetValue(device.SerialNumber, out currentDevice); else // insert a new device currentDevice = new Device(); currentDevice.SerialNumber = device.SerialNumber; currentDevice.SerialNumberTABS = device.SerialNumberTabs; currentDevice.Model = device.Model; if (device.CustomerAccountID != null && device.CustomerAccountID != "") { companyMap.TryGetValue(device.CustomerAccountID, out tempCompany); currentDevice.CustomerID = tempCompany.CompanyID; currentDevice.CustomerName = tempCompany.CompanyName; } if (companyMap.TryGetValue(device.ServicingDealerAccountID, out tempCompany)) currentDevice.CompanyID = tempCompany.CompanyID; currentDevice.StatusID = 1; currentDevice.Retries = 0; currentDevice.ControllerFamilyID = 1; if (currentDevice.EWBFrontPanelMsgOption == null) // set the Panel option to the default if it isn't set already currentDevice.EWBFrontPanelMsgOption = context.EWBFrontPanelMsgOptions.Where( i => i.OptionDescription.Contains("default")).Single(); // link the device to the existing address as long as it is actually an address if (addressMap.TryGetValue(GetAddressIdentifier(device.address), out tempAddress)) { if (GetAddressIdentifier(device.address) != "") currentDevice.Address = tempAddress; else currentDevice.Address = null; } else // insert a new Address and link the device to it (if not null) { if (GetAddressIdentifier(device.address) == "") currentDevice.Address = null; else { tempAddress = new Address(); tempAddress.Address1 = device.address.Address1; tempAddress.Address2 = device.address.Address2; tempAddress.Address3 = device.address.Address3; tempAddress.Address4 = device.address.Address4; tempAddress.City = device.address.City; tempAddress.Country = device.address.Country; tempAddress.PostalCode = device.address.PostalCode; tempAddress.State = device.address.State; addresses.AddObject(tempAddress); addressMap.Add(GetAddressIdentifier(tempAddress), tempAddress); currentDevice.Address = tempAddress; } } if (!deviceMap.ContainsKey(device.SerialNumber)) // if inserting, add to context { oldDevices.AddObject(currentDevice); deviceMap.Add(device.SerialNumber, currentDevice); } } context.SaveChanges();

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  • PostgreSQL - fetch the row which has the Max value for a column

    - by Joshua Berry
    I'm dealing with a Postgres table (called "lives") that contains records with columns for time_stamp, usr_id, transaction_id, and lives_remaining. I need a query that will give me the most recent lives_remaining total for each usr_id There are multiple users (distinct usr_id's) time_stamp is not a unique identifier: sometimes user events (one by row in the table) will occur with the same time_stamp. trans_id is unique only for very small time ranges: over time it repeats remaining_lives (for a given user) can both increase and decrease over time example: time_stamp|lives_remaining|usr_id|trans_id ----------------------------------------- 07:00 | 1 | 1 | 1 09:00 | 4 | 2 | 2 10:00 | 2 | 3 | 3 10:00 | 1 | 2 | 4 11:00 | 4 | 1 | 5 11:00 | 3 | 1 | 6 13:00 | 3 | 3 | 1 As I will need to access other columns of the row with the latest data for each given usr_id, I need a query that gives a result like this: time_stamp|lives_remaining|usr_id|trans_id ----------------------------------------- 11:00 | 3 | 1 | 6 10:00 | 1 | 2 | 4 13:00 | 3 | 3 | 1 As mentioned, each usr_id can gain or lose lives, and sometimes these timestamped events occur so close together that they have the same timestamp! Therefore this query won't work: SELECT b.time_stamp,b.lives_remaining,b.usr_id,b.trans_id FROM (SELECT usr_id, max(time_stamp) AS max_timestamp FROM lives GROUP BY usr_id ORDER BY usr_id) a JOIN lives b ON a.max_timestamp = b.time_stamp Instead, I need to use both time_stamp (first) and trans_id (second) to identify the correct row. I also then need to pass that information from the subquery to the main query that will provide the data for the other columns of the appropriate rows. This is the hacked up query that I've gotten to work: SELECT b.time_stamp,b.lives_remaining,b.usr_id,b.trans_id FROM (SELECT usr_id, max(time_stamp || '*' || trans_id) AS max_timestamp_transid FROM lives GROUP BY usr_id ORDER BY usr_id) a JOIN lives b ON a.max_timestamp_transid = b.time_stamp || '*' || b.trans_id ORDER BY b.usr_id Okay, so this works, but I don't like it. It requires a query within a query, a self join, and it seems to me that it could be much simpler by grabbing the row that MAX found to have the largest timestamp and trans_id. The table "lives" has tens of millions of rows to parse, so I'd like this query to be as fast and efficient as possible. I'm new to RDBM and Postgres in particular, so I know that I need to make effective use of the proper indexes. I'm a bit lost on how to optimize. I found a similar discussion here. Can I perform some type of Postgres equivalent to an Oracle analytic function? Any advice on accessing related column information used by an aggregate function (like MAX), creating indexes, and creating better queries would be much appreciated! P.S. You can use the following to create my example case: create TABLE lives (time_stamp timestamp, lives_remaining integer, usr_id integer, trans_id integer); insert into lives values ('2000-01-01 07:00', 1, 1, 1); insert into lives values ('2000-01-01 09:00', 4, 2, 2); insert into lives values ('2000-01-01 10:00', 2, 3, 3); insert into lives values ('2000-01-01 10:00', 1, 2, 4); insert into lives values ('2000-01-01 11:00', 4, 1, 5); insert into lives values ('2000-01-01 11:00', 3, 1, 6); insert into lives values ('2000-01-01 13:00', 3, 3, 1);

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  • Autoincrement uniqueidentifier in C#

    - by drasto
    Basically I want to use uniqueidentifier in similar way as identity. I don't want to insert values into it, It should just insert values automatically, different value for each row. I'm not able to set autoincrement on columns of type uniqueidentifier(the property 'autoincrement' is set to false and is not editable).

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