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  • How to get top 3 frequencies in MySQL?

    - by Amenhotep
    Hello, In MySQL I have a table called "meanings" with three columns: "person" (int), "word" (byte, 16 possible values) "meaning" (byte, 26 possible values). A person assigns one or more meanings to each word: person word meaning ------------------- 1 1 4 1 2 19 1 2 7 <-- second meaning for word 2 1 3 5 ... 1 16 2 Then another person, and so on. There will be thousands of persons. I need to find for each of the 16 words the top three meanings (with their frequencies). Something like: word 1: meaning 5 (35% of people), meaning 19 (22% of people), meaning 2 (13% of people) word 2: meaning 8 (57%), meaning 1 (18%), meaning 22 (7%) ... Is it possible to solve this with a single MySQL query? (If this problem is a classic one and has been answered elsewhere, I would appreciate if you could give me a link to the solution.) Thank you very much, ve

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  • Is closing/disposing an SqlDataReader needed if you are already closing the sqlconnection?

    - by Brian
    I noticed This question, but my question is a bit more specific. Is there any advantage to using using (SqlConnection conn = new SqlConnection(conStr)) { using (SqlCommand command = new SqlCommand()) { // dostuff } } instead of using (SqlConnection conn = new SqlConnection(conStr)) { SqlCommand command = new SqlCommand(); // dostuff } Obviously it does matter run more than one command with the same connection, since closing an SqlDataReader is more efficient than closing and reopening a connection (calling conn.Close();conn.Open(); will also free up the connection). I see many people insist that failure to close the DataReader means leaving open connection resources around, but doesn't that only apply if you don't close the connection?

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  • LINQtoSQL: Query to return List<String>

    - by ctrlShiftBryan
    I have a LINQ query that returns some object like this... var query = from c in db.Customers where ... select c; Then I do this List<String> list = new List<String>(); foreach (ProgramLanguage c in query) { //GetUL returns a String list.Add(GetUL(c.Property,c.Property2)); } Is there a way to combine into something list this? var query = from c in db.Customers where ... select new { GetUL(c.Property,c.Property2) }).ToList<String>();

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  • how do i connect to MSSQL 2008 database in JAVA with jbbc

    - by shuxer
    Hello I have MSSQL 2008 installed on my local PC, and my java application needs to connect to a mssql database. I am a new to MSSQL and i would like get some help on creating user login for my java application and getting connection via jdbc. So far i tried to create a user login for my app and used following connection string, but i doest work at all. Any help and hint will be appreciated. jdbc:jtds:sqlserver://127.0.0.1:1433/dotcms username="shuxer" password="itarator" Thanks in advance.

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  • Subquery works in 9i but not in 11g

    - by Zsuetam
    Statement below is working on Oracle 9i but not on Oracle 11g SELECT * FROM ( SELECT 0 scrnfail_rate, '9' zz, 7 hh FROM DUAL UNION ALL SELECT 0 scrnfail_rate, '9' zz, 7 hh FROM DUAL ) WHERE zz IS NOT NULL AND TO_CHAR (hh) NOT IN ( SELECT DECODE ( scrnfail_rate, 0, -1, ROUND (LEVEL * 1 / (scrnfail_rate / 100)) - ROUND (1 / (2 * (scrnfail_rate / 100))) ) AS nno FROM DUAL WHERE NVL (scrnfail_rate, 0) > 0 CONNECT BY LEVEL <= ROUND(9 * scrnfail_rate / 100) ) It looks like Oracle 11g is ignoring where decode or even where clause in the subquery. This query should return two rows as it does on Oracle 9i, but results ORA-01476: divisor is equal to zero on Oracle 11g EE 11.2.0.1.0 - 64bit. Can anyone help? Thanks!

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  • Thinking of an Inner Join as a Cross Join and then satisfying some condition(s)?

    - by Jian Lin
    It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then satisfying some condition(s)? Because the equi-join can be obvious, but the non-equi-join can be a bit confusing. But if we always use the Cross Join, and then filter out the ones satisfying the condition, then we get the resulting table. In other words, we can always analyze it by using the first record on the left table, and then go through every single records on the right, and then repeat that for 2nd record on the left, and for the 3rd, 4th, ... etc. So in our mind, we can analyze it using this way, and it is like O(n^2), although what happens in the DBMS maybe that it is a lot faster (when an index is present). Is there another good way to think of it besides this method?

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  • Better way to do SELECT with GROUP BY

    - by Luca Romagnoli
    Hi i've wrote a query that works: SELECT `comments`.* FROM `comments` RIGHT JOIN (SELECT MAX( id ) AS id, core_id, topic_id FROM comments GROUP BY core_id, topic_id order by id desc) comm ON comm.id = comments.id LIMIT 10 I want know if it is possible (and how) to rewrite it to get better performance. Thanks

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  • The Next-gen Databases

    - by Randin
    I'm learning traditional Relational Databases (with PostgreSQL) and doing some research I've come across some new types of databases. CouchDB, Drizzle, and Scalaris to name a few, what is going to be the next database technologies to deal with?

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  • radgridview delete update in asp.net

    - by abhi
    i have written the follwing to display data from the datagrid and den insert new rows but how do i perform update and delete plss help here's my code using System; using System.Data; using System.Configuration; using System.Collections; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; using Telerik.Web.UI; using System.Data.SqlClient; public partial class Default6 : System.Web.UI.Page { string strQry, strCon; SqlDataAdapter da; SqlConnection con; DataSet ds; protected void Page_Load(object sender, EventArgs e) { strCon = "Data Source=MINETDEVDATA; Initial Catalog=ML_SuppliersProd; User Id=sa; Password=@MinetApps7;"; con = new SqlConnection(strCon); strQry = "SELECT * FROM table1"; da = new SqlDataAdapter(strQry, con); SqlCommandBuilder cmdbuild = new SqlCommandBuilder(da); ds = new DataSet(); da.Fill(ds, "table1"); RadGrid1.DataSource = ds.Tables["table1"]; RadGrid1.DataBind(); Label3.Visible = false; Label4.Visible = false; Label5.Visible = false; txtFname.Visible = false; txtLname.Visible = false; txtDesignation.Visible = false; } protected void Submit_Click(object sender, EventArgs e) { Label3.Visible = true; Label4.Visible = true; Label5.Visible = true; txtFname.Visible = true; txtLname.Visible = true; txtDesignation.Visible = true; } protected void Button2_Click(object sender, EventArgs e) { DataSet ds = new DataSet("EmployeeSet"); da.Fill(ds, "table1"); DataTable EmployeeTable = ds.Tables["table1"]; DataRow row = EmployeeTable.NewRow(); row["Fname"] = txtFname.Text.ToString(); row["Lname"] = txtLname.Text.ToString(); row["Designation"] = txtDesignation.Text.ToString(); EmployeeTable.Rows.Add(row); da.Update(ds, "table1"); //RadGrid1.DataSource = ds.Tables["table1"]; //RadGrid1.DataBind(); txtFname.Text = ""; txtLname.Text = ""; txtDesignation.Text = ""; } protected void RadGrid1_DeleteCommand(object source, GridCommandEventArgs e) { } } }

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  • How to use a getter with a nullable?

    - by Desmond Lost
    I am reading a bunch of queries from a database. I had an issue with the queries not closing, so I added a CommandTimeout. Now, the individual queries read from the config file each time they are run. How would I make the code cache the int from the config file only once using a static nullable and getter. I was thinking of doing something along the lines of: static int? var; get{ var = null; if (var.HasValue) ...(i dont know how to complete the rest) My actual code: private object ExecuteQuery(string dbConnStr, bool fixIt) { object result = false; using (SqlConnection connection = new SqlConnection(dbConnStr)) { connection.Open(); using (SqlCommand sqlCmd = new SqlCommand()) { AddSQLParms(sqlCmd); sqlCmd.CommandTimeout = 30; sqlCmd.CommandText = _cmdText; sqlCmd.Connection = connection; sqlCmd.CommandType = System.Data.CommandType.Text; sqlCmd.ExecuteNonQuery(); } connection.Close(); } return result; }}

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  • Cassandra Production ready on Windows?

    - by BlackTea
    Question anyone know of any success stories of Cassandra running on windows in a production environment? I'm doing some work on Cassandra and trying to find the correct platform for it currently the platform is windows running MS-SQLas the data store. what are the dis-advantages if any when running Cassandra on a windows environment.

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  • rookie MySql question about paging; Is one query enough?

    - by Camran
    I have managed to get paging to work, almost. I want to display to the user, total nr of records found, and the currently displayed records. Ex: 4000 found, displaying 0-100. I am testing this with the nr 2 (because I don't have that many records, have like 20). So I am using LIMIT $start, $nr_results; Do I have to make two queries in order to display the results the way I want, one query fetching all records and then make a mysql_num_rows to get all records, then the one with the LIMIT ? I have this: mysql_num_rows($qry_result); $total_pages = ceil($num_total / $res_per_page); //$res_per_page==2 and $num_total = 2 if ($p - 10 < 1) { $pagemin=1; } else { $pagemin = $p - 10; } if ($p + 10 $total_pages) { $pagemax = $total_pages; } else { $pagemax = $p + 10; } Here is the query: SELECT mt.*, fordon.*, boende.*, elektronik.*, business.*, hem_inredning.*, hobby.* FROM classified mt LEFT JOIN fordon ON fordon.classified_id = mt.classified_id LEFT JOIN boende ON boende.classified_id = mt.classified_id LEFT JOIN elektronik ON elektronik.classified_id = mt.classified_id LEFT JOIN business ON business.classified_id = mt.classified_id LEFT JOIN hem_inredning ON hem_inredning.classified_id = mt.classified_id LEFT JOIN hobby ON hobby.classified_id = mt.classified_id ORDER BY modify_date DESC LIMIT 0, 2 Thanks, if you need more input let me know. Basically Q is, do I have to make two queries?

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  • Insert multiple records from a XML string differing on one parameter in SQL SERVER 2008

    - by Rohit
    Below in a query which inserts records to SimpleDictationProfileMapping table after reading it from a XML string. Now this query inserts a single record in which DictationCaptureProfileID is @dictationCaptureProfileId . Now i want to insert multiple rows in which @dictationCaptureProfileId is different and other 2 values are same. What i want to achieve by this is in case parent changes all child values should also change. INSERT INTO SimpleDictationProfileMapping ( DictationCaptureProfileID, DictationProfileMappingAttributeID, DictationProfileMappingAttributeValue ) SELECT @dictationCaptureProfileId, row.value('@attrId','varchar(max)'), row.value('@value', 'varchar(max)') FROM @simpleDictationCaptureProfileMappings.nodes('/simpleMappingAtribute/attribute') AS d ( row ) ; I want INSERT INTO SimpleDictationProfileMapping ( DictationCaptureProfileID OR (SELECT DictationCaptureProfileID FROM DictationCaptureProfile WHERE SystemDictationCaptureProfileID = @systemDictationCaptureProfileID), DictationProfileMappingAttributeID, DictationProfileMappingAttributeValue ) SELECT @dictationCaptureProfileId , row.value('@attrId','varchar(max)'), row.value('@value', 'varchar(max)') FROM @simpleDictationCaptureProfileMappings.nodes ('/simpleMappingAtribute/attribute') AS d ( row ) ; Please tell how to achieve this.

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  • IN statement performance in PostgreSQL (and in general)

    - by Vasil
    I know this has probably been asked before, but I can't find it with SO's search. Lets say i've TABLE1 and TABLE2, who should I expect the performance of a query such as this: SELECT * FROM TABLE1 WHERE id IN SUBQUERY_ON_TABLE2; as the number of rows in TABLE1 and TABLE2 grow and id is a primary key on TABLE1. Yes, I know using IN is such a n00b mistake, but TABLE2 has a generic relation (django generic relation) to multiple other tables so I can't think of another way to filter the data. At what (aproximate) ammount of rows in TABLE1 and TABLE2 should I expect to notice performance issues because of this? Will performance degrade linearly, exponentially etc. depending on the number of rows?

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  • Delete a Row from a DataGridView given its index

    - by Ruben Trancoso
    My DataGridView is a single line selection and theres a rowEnter Event where I get the line index every time the selected line changes. private void rowEnter(object sender, DataGridViewCellEventArgs e) { currentRowIndex = e.RowIndex; } when I press a delete button I use the same index to delete the row myDataSet.Avaliado.Rows[currentRowIndex].Delete(); avaliadoTableAdapter.Update(myDataSet.Avaliado); it works fine if no column in the DataGridView is sorted, otherwise a get an error. What should be the way to know the row index in the dataset that corresponds to the rowindex from the DataGridView?

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  • Copying Some from a PostgreSQL Server to Another

    - by whollychao
    I am in need of an application that can periodically transmit select rows from a PostgreSQL database across a network to a second PostgreSQL server. Typically these will be the most recent row added, pulled and transmitted every 10-30 seconds. The primary servers run in a MS Windows environment with a high-latency, and occasionally intermittent, network connection. Therefore, any application would have to be tolerant of this and ideally automatically reconnect / resend data that could not be transmitted. Due to the environment and the requirements, a full-blown replication package would be unnecessary. I appreciate any help anyone has with this problem.

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  • Speeding up PostgreSQL query where data is between two dates

    - by Roger
    I have a large table ( 50m rows) which has some data with an ID and timestamp. I need to query the table to select all rows with a certain ID where the timestamp is between two dates, but it currently takes over 2 minutes on a high end machine. I'd really like to speed it up. I have found this tip which recommends using a spatial index, but the example it gives is for IP addresses. However, the speed increase (436s to 3s) is impressive. How can I use this with timestamps?

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  • Put logic behind generated LinqToSql fields

    - by boris callens
    In a database I use throughout several projects, there is a field that should actually be a boolean but is for reasons nobody can explain to me a field duplicated over two tables where one time it is a char ('Y'/'N') and one time an int (1/0). When I generate a datacontext with LinqToSql the fields off course gets these datatypes. It would be nice if I don't have to drag this stupid choice of datatype throughout the rest of my application. Is there a way to give the generated classes a little bit of logic that just return me return this.equals('Y'); and return this==1; Preferably without having to make an EXTRA field in my partial class. It would be a solution to give the generated field a totally different name that can only be accessed through the partial class and then generate the extra field with the original name with my custom logic in the partial class. I don't know how to alter the accesibility level in my generated class though.. Any suggestions?

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  • Avoiding Nested Queries

    - by Midhat
    How Important is it to avoid nested queries. I have always learnt to avoid them like a plague. But they are the most natural thing to me. When I am designing a query, the first thing I write is a nested query. Then I convert it to joins, which sometimes takes a lot of time to get right. And rarely gives a big performance improvement (sometimes it does) So are they really so bad. Is there a way to use nested queries without temp tables and filesort

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  • Database design - alternatives for Entity Attribute Value (AEV)

    - by Bob
    Hi, see http://stackoverflow.com/questions/695752/product-table-many-kinds-of-product-each-product-has-many-parameters for similar topic. My question: i want to design a database, that will be used for a production facility of different types of products where each product has its own (number of) parameters. because i want the serial numbers to be in one tabel for overview purposes i have a problem with these different paraeters . One solution could be AEV, but it has its downsides, certainly because we have +- 5 products with every product +- 20.000 serial numbers (records). it looks a bit overkill to me... I just don't know how one could design a database so that you have an attribute in a mastertable that says: 'hey, you could find details of this record in THAT detail-table". 'in a way that you qould easely query the results) currenty i am using Visual Basic & Acces 2007. but i'm going to Visual Basic & MySQL. thanks for your help. Bob

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