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  • Best practice for avoiding locks on a heavily read table?

    - by Luiggi
    Hi, I have a big database (~4GB), with 2 large tables (~3M records) having ~180K SELECTs/hour, ~2k UPDATEs/hour and ~1k INSERTs+DELETEs/hour. What would be the best practice to guarantee no locks for the reading tasks while inserting/updating/deleting? I was thinking about using a NOLOCK hint, but there is so much discussed about this (is good, is bad, it depends) that I'm a bit lost. I must say I've tried this in a dev environment and I didn't find any problems, but I don't want to put it on production until I get some feedback... Thank you! Luiggi

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  • An attempt to attach an auto-named database for file failed in Vb.Net

    - by user2454135
    I am Trying to connect database for first time , and I am getting this error : An attempt to attach an auto-named database for file VBTestDB.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share. and getting error on myconnect.Open() Heres my code : Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim myconnect As New SqlClient.SqlConnection myconnect.ConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=VBTestDB.mdf;Integrated Security=True;User Instance=True;" Dim mycommand As SqlClient.SqlCommand = New SqlClient.SqlCommand() mycommand.Connection = myconnect mycommand.CommandText = "INSERT INTO Card (CardNo,Name) VALUES (@cardno,@name)" myconnect.Open() Try mycommand.Parameters.Add("@cardno", SqlDbType.Int).Value = TextBox1.Text mycommand.Parameters.Add("@name", SqlDbType.NVarChar).Value = TextBox2.Text mycommand.ExecuteNonQuery() MsgBox("Success") Catch ex As System.Data.SqlClient.SqlException MsgBox(ex.Message) End Try myconnect.Close() End Sub

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  • Speeding up a group by date query on a big table in postgres

    - by zaius
    I've got a table with around 20 million rows. For arguments sake, lets say there are two columns in the table - an id and a timestamp. I'm trying to get a count of the number of items per day. Here's what I have at the moment. SELECT DATE(timestamp) AS day, COUNT(*) FROM actions WHERE DATE(timestamp) >= '20100101' AND DATE(timestamp) < '20110101' GROUP BY day; Without any indices, this takes about a 30s to run on my machine. Here's the explain analyze output: GroupAggregate (cost=675462.78..676813.42 rows=46532 width=8) (actual time=24467.404..32417.643 rows=346 loops=1) -> Sort (cost=675462.78..675680.34 rows=87021 width=8) (actual time=24466.730..29071.438 rows=17321121 loops=1) Sort Key: (date("timestamp")) Sort Method: external merge Disk: 372496kB -> Seq Scan on actions (cost=0.00..667133.11 rows=87021 width=8) (actual time=1.981..12368.186 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 32447.762 ms Since I'm seeing a sequential scan, I tried to index on the date aggregate CREATE INDEX ON actions (DATE(timestamp)); Which cuts the speed by about 50%. HashAggregate (cost=796710.64..796716.19 rows=370 width=8) (actual time=17038.503..17038.590 rows=346 loops=1) -> Seq Scan on actions (cost=0.00..710202.27 rows=17301674 width=8) (actual time=1.745..12080.877 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 17038.663 ms I'm new to this whole query-optimization business, and I have no idea what to do next. Any clues how I could get this query running faster?

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  • Join using combined conditions on one join table

    - by Nathan Wienert
    I have join a table joining songs to genres. The table has a 'source' column that's used to identify where the genre was found. Genres are found from blogs, artists, tags, and posts. So, songs | song_genre | genres id | song_id, source, genre_id | id What I want to build is a song SELECT query that works something like this, given I already have a genre_id: IF exists song_genre with source='artist' AND a song_genre with source='blog' OR exists song_genre with source='artist' AND a song_genre with source='post' OR exists song_genre with source='tag' I'm was going to do it by doing a bunch of joins, but am sure I'm not doing it very well. Using Postgres 9.1.

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  • LINQ - 'Could not translate expression' with previously used and proven query condition

    - by tomfumb
    I am fairly new to LINQ and can't get my head around some inconsistency in behaviour. Any knowledgeable input would be much appreciated. I see similar issues on SO and elsewhere but they don't seem to help. I have a very simple setup - a company table and an addresses table. Each company can have 0 or more addresses, and if 0 one must be specified as the main address. I'm trying to handle the cases where there are 0 addresses, using an outer join and altering the select statement accordingly. Please note I'm currently binding the output straight to a GridView so I would like to keep all processing within the query. The following DOES work IQueryable query = from comp in context.Companies join addr in context.Addresses on comp.CompanyID equals addr.CompanyID into outer // outer join companies to addresses table to include companies with no address from addr in outer.DefaultIfEmpty() where (addr.IsMain == null ? true : addr.IsMain) == true // if a company has no address ensure it is not ruled out by the IsMain condition - default to true if null select new { comp.CompanyID, comp.Name, AddressID = (addr.AddressID == null ? -1 : addr.AddressID), // use -1 to represent a company that has no addresses MainAddress = String.Format("{0}, {1}, {2} {3} ({4})", addr.Address1, addr.City, addr.Region, addr.PostalCode, addr.Country) }; but this displays an empty address in the GridView as ", , ()" So I updated the MainAddress field to be MainAddress = (addr.AddressID == null ? "" : String.Format("{0}, {1}, {2} {3} ({4})", addr.Address1, addr.City, addr.Region, addr.PostalCode, addr.Country)) and now I'm getting the Could not translate expression error and a bunch of spewey auto-generated code in the error which means very little to me. The condition I added to MainAddress is no different to the working condition on AddressID, so can anybody tell me what's going on here? Any help greatly appreciated.

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  • Problem with DB2 Over clause

    - by silent1mezzo
    I'm trying to do pagination with a very old version of DB2 and the only way I could figure out selecting a range of rows was to use the OVER command. This query provide's the correct results (the results that I want to paginate over). select MIN(REFID) as REFID, REFGROUPID from ARMS_REFERRAL where REFERRAL_ID<>'Draft' and REFERRAL_ID not like 'Demo%' group by REFGROUPID order by REFID desc Results: REFID REFGROUPID 302 242 301 241 281 221 261 201 225 142 221 161 ... ... SELECT * FROM ( SELECT row_number() OVER () AS rid, MIN(REFID) AS REFID, REFGROUPID FROM arms_referral where REFERRAL_ID<>'Draft' and REFERRAL_ID not like 'Demo%' group by REFGROUPID order by REFID desc ) AS t WHERE t.rid BETWEEN 1 and 5 Results: REFID REFGROUPID 26 12 22 11 14 8 11 7 6 4 As you can see, it does select the first five rows, but it's obviously not selecting the latest. If I add a Order By clause to the OVER() it gets closer, but still not totally correct. SELECT * FROM ( SELECT row_number() OVER (ORDER BY REFGROUPID desc) AS rid, MIN(REFID) AS REFID, REFGROUPID FROM arms_referral where REFERRAL_ID<>'Draft' and REFERRAL_ID not like 'Demo%' group by REFGROUPID order by REFID desc ) AS t WHERE t.rid BETWEEN 1 and 5 REFID REFGROUPID 302 242 301 241 281 221 261 201 221 161 It's really close but the 5th result isn't correct (actually the 6th result). How do I make this query correct so it can group by a REFGROUPID and then order by the REFID?

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  • How to differenciate two tables

    - by Nemat
    Hi friends.... I have two tables.I want to get all records from one table that are different from the records in second table. For eg. if we have four records in first table like A,B,C,D and three records in second table thats A,B,C then the answer of query should be D. I have tried "EXCEPT" operator but it doesnt work fine.Kindly help me in writing correct query for the given problem. Any help is appreciated.... Thanks in Advance Nemat

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  • Insert or update when product is present using mysql

    - by Aryan
    main_product table productid outward shopid 333 2 44//present 343 4 44//present 353 5 44//present 363 1 44//present 373 2 44//not present min_product table productid outward shopid 333 1 44 343 1 44 353 1 44 363 1 44 SELECT DISTINCT (A.productid),A.outward, B.productid,B.outward FROM main_product A INNER JOIN min_product B on B.productid=A.product_id where A.shopid='44' and B.shopid='44' my question how can i INSERT OR UPDATE in one query using mysql by checking if it is present or not if present update else insert something like this? INSERT INTO mytable (key, value) VALUES ($newkey, $newvalue) ON DUPLICATE KEY UPDATE SET value = $newvalue

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  • Consolidating separate Loan, Purchase & Sales tables into one transaction table.

    - by Frank Computer
    INFORMIX-SE with ISQL 7.3: I have separate tables for Loan, Purchase & Sales transactions. Each tables rows are joined to their respective customer rows by: customer.id [serial] = loan.foreign_id [integer]; = purchase.foreign_id [integer]; = sale.foreign_id [integer]; I would like to consolidate the three tables into one table called "transaction", where a column "transaction.trx_type" [char(1)] {L=Loan, P=Purchase, S=Sale} identifies the transaction type. Is this a good idea or is it better to keep them in separate tables? Storage space is not a concern, I think it would be easier programming & user=wise to have all types of transactions under one table.

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  • mysql join table - selecting the newest row

    - by cmancre
    Hi, I have the following two MySQL tables TABLE NAMES NAME_ID NAME 1 name1 2 name2 3 name3 TABLE STATUS STATUS_ID NAME_ID TIMESTAMP 1 1 2010-12-20 12:00 2 2 2010-12-20 10:00 3 3 2010-12-20 10:30 4 3 2010-12-20 14:00 I would like to select all info from table NAMES and add most recent correspondent TIMESTAMP column from table STATUS RESULT NAME_ID NAME TIMESTAMP 1 name1 2010-12-20 12:00 2 name2 2010-12-20 10:00 3 name3 2010-12-20 14:00 Am stuck on this one. How do I left join only on the newer timestamp?

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  • Doubt in stored procedure in asp.net

    - by Surya sasidhar
    hi, i am writing a sotreprocedure displaying month and year it is working but it is not coming in a order descending order can u help me my procedure like below... ALTER procedure [dbo].[audioblog_getarchivedates] as begin select DateName(Month,a.createddate) + ' ' + DateName(Year,a.createddate) as ArchiveDate from audio_blog a group by DateName(Month,a.createddate) + ' ' + DateName(Year,a.createddate) order by DateName(Month,a.createddate) + ' ' + DateName(Year,a.createddate) desc end result will come like this March 2010 January 2010 February 2010 but it is not in a order (desc) can u help me

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  • Index View Index Creation Failing

    - by aBetterGamer
    I'm trying to create an index on a view and it keeps failing, I'm pretty sure its b/c I'm using an alias for the column. Not sure how or if I can do it this way. Below is a simplified scenario. CREATE VIEW v_contracts WITH SCHEMABINDING AS SELECT t1.contractid as 'Contract.ContractID' t2.name as 'Customer.Name' FROM contract t1 JOIN customer t2 ON t1.contractid = t2.contractid GO CREATE UNIQUE CLUSTERED INDEX v_contracts_idx ON v_contracts(t1.contractid) GO --------------------------- Incorrect syntax near '.'. CREATE UNIQUE CLUSTERED INDEX v_contracts_idx ON v_contracts(contractid) GO --------------------------- Column name 'contractid' does not exist in the target table or view. CREATE UNIQUE CLUSTERED INDEX v_contracts_idx ON v_contracts(Contract.ContractID) GO --------------------------- Incorrect syntax near '.'. Anyone know how to create an indexed view using aliased columns please let me know.

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  • How to use php variables (arrays) in mysql select statements?

    - by davidconn
    Hi everybody, How do you use a php variable (array) inside a mysql select statement? I am designing an auction site and currently working on a page that lets people view a list of all the current bids for an item. I want to display 3 columns: amountbid - the amount each bidder has bid for the item (held in tblbid) bidderid - the id of each bidder who has bid (found in tbluser) total_positivity_feedback - how many users have left positive feedback for the bidder (calculated from tblfeedback) To find the 'amount' and the 'bidderid' columns i pass the essayid URL parameter from the previous page. This works fine. Despite this, i can't display the total_positivity_feedback column for the various users who have made each bid. My mysql query looks like this: select tblbid.bidderid, tblbid.amount, (select count(tblfeedback.feedbackid) from tblfeedback WHERE tblfeedback.writerid = "ARRAY VARIABLE GOES HERE") AS total_positivity_feedback FROM tblbid WHERE tblbid.essayid = $essayid_bids I assume that the only way to accomplish this is to make the variable contain the bidderid's of those people who bid for that particular essay? I can't seem to work out how to do this tho?!? Many thanks for your help

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  • self join table

    - by San82moon
    HI, i have a table, new_id----old_id----created_on 1234------5678------20100912 5678------3456------20100808 etc. i wrote this query, $q = "select event1.new_id, event1.old_id, event1.created_on,event2.new_id, event2.old_id, event2.created_on FROM replaced_isbns event1 JOIN replaced_isbns event2 ON event2.new_id = event1.old_id WHERE event1.new_id='$id'"; but i get result as 5678 - 1234, ie only one row, i want all rows... plz help me. Thanks, SLC

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  • Why is it possible to enumerate a LinqToSql query after calling Dispose() on the DataContext?

    - by DanM
    I'm using the Repository Pattern with some LinqToSql objects. My repository objects all implement IDisposable, and the Dispose() method does only thing--calls Dispose() on the DataContext. Whenever I use a repository, I wrap it in a using person, like this: public IEnumerable<Person> SelectPersons() { using (var repository = _repositorySource.GetNew<Person>(dc => dc.Person)) { return repository.GetAll(); } } This method returns an IEnumerable<Person>, so if my understanding is correct, no querying of the database actually takes place until Enumerable<Person> is traversed (e.g., by converting it to a list or array or by using it in a foreach loop), as in this example: var persons = gateway.SelectPersons(); // Dispose() is fired here var personViewModels = ( from b in persons select new PersonViewModel { Id = b.Id, Name = b.Name, Age = b.Age, OrdersCount = b.Order.Count() }).ToList(); // executes queries In this example, Dispose() gets called immediately after setting persons, which is an IEnumerable<Person>, and that's the only time it gets called. So, a couple questions: How does this work? How can a disposed DataContext still query the database for results when I walk the IEnumerable<Person>? What does Dispose() actually do? I've heard that it is not necessary (e.g., see this question) to dispose of a DataContext, but my impression was that it's not a bad idea. Is there any reason not to dispose of it?

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  • LinqtoSql Pre-compile Query problem with Count() on a group by

    - by Joe Pitz
    Have a LinqtoSql query that I now want to precompile. var unorderedc = from insp in sq.Inspections where insp.TestTimeStamp > dStartTime && insp.TestTimeStamp < dEndTime && insp.Model == "EP" && insp.TestResults != "P" group insp by new { insp.TestResults, insp.FailStep } into grp select new { FailedCount = (grp.Key.TestResults == "F" ? grp.Count() : 0), CancelCount = (grp.Key.TestResults == "C" ? grp.Count() : 0), grp.Key.TestResults, grp.Key.FailStep, PercentFailed = Convert.ToDecimal(1.0 * grp.Count() / tcount * 100) }; I have created this delegate: public static readonly Funct<SQLDataDataContext, int, string, string, DateTime, DateTime, IQueryable<CalcFailedTestResult>> GetInspData = CompiledQuery.Compile((SQLDataDataContext sq, int tcount, string strModel, string strTest, DateTime dStartTime, DateTime dEndTime, IQueryable<CalcFailedTestResult> CalcFailed) => from insp in sq.Inspections where insp.TestTimeStamp > dStartTime && insp.TestTimeStamp < dEndTime && insp.Model == strModel && insp.TestResults != strTest group insp by new { insp.TestResults, insp.FailStep } into grp select new { FailedCount = (grp.Key.TestResults == "F" ? grp.Count() : 0), CancelCount = (grp.Key.TestResults == "C" ? grp.Count() : 0), grp.Key.TestResults, grp.Key.FailStep, PercentFailed = Convert.ToDecimal(1.0 * grp.Count() / tcount * 100) }); The syntax error is on the CompileQuery.Compile() statement It appears to be related to the use of the select new {} syntax. In other pre-compiled queries I have written I have had to just use the select projection by it self. In this case I need to perform the grp.count() and the immediate if logic. I have searched SO and other references but cannot find the answer.

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