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  • Representing Sparse Data in PostgreSQL

    - by Chris S
    What's the best way to represent a sparse data matrix in PostgreSQL? The two obvious methods I see are: Store data in a single a table with a separate column for every conceivable feature (potentially millions), but with a default value of NULL for unused features. This is conceptually very simple, but I know that with most RDMS implementations, that this is typically very inefficient, since the NULL values ususually takes up some space. However, I read an article (can't find its link unfortunately) that claimed PG doesn't take up data for NULL values, making it better suited for storing sparse data. Create separate "row" and "column" tables, as well as an intermediate table to link them and store the value for the column at that row. I believe this is the more traditional RDMS solution, but there's more complexity and overhead associated with it. I also found PostgreDynamic, which claims to better support sparse data, but I don't want to switch my entire database server to a PG fork just for this feature. Are there any other solutions? Which one should I use?

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  • Testing the context in asp.net mvc

    - by user252160
    I got pretty experienced with testing controllers, my question here is though, aren't we supposed to test the data context as well, and how ? I mean, there are a lot of relationships and constraints coming from the DB that simply testing controllers does not cover. On the other hand, testing against the DB is not considered a good practice - what then ? Simply testing without db.SubmitChanges() or what ?

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  • Select number of rows for each group where two column values makes one group

    - by Fábio Antunes
    I have a two select statements joined by UNION ALL. In the first statement a where clause gathers only rows that have been shown previously to the user. The second statement gathers all rows that haven't been shown to the user, therefore I end up with the viewed results first and non-viewed results after. Of course this could simply be achieved with the same select statement using a simple ORDER BY, however the reason for two separate selects is simple after you realize what I hope to accomplish. Consider the following structure and data. +----+------+-----+--------+------+ | id | from | to | viewed | data | +----+------+-----+--------+------+ | 1 | 1 | 10 | true | .... | | 2 | 10 | 1 | true | .... | | 3 | 1 | 10 | true | .... | | 4 | 6 | 8 | true | .... | | 5 | 1 | 10 | true | .... | | 6 | 10 | 1 | true | .... | | 7 | 8 | 6 | true | .... | | 8 | 10 | 1 | true | .... | | 9 | 6 | 8 | true | .... | | 10 | 2 | 3 | true | .... | | 11 | 1 | 10 | true | .... | | 12 | 8 | 6 | true | .... | | 13 | 10 | 1 | false | .... | | 14 | 1 | 10 | false | .... | | 15 | 6 | 8 | false | .... | | 16 | 10 | 1 | false | .... | | 17 | 8 | 6 | false | .... | | 18 | 3 | 2 | false | .... | +----+------+-----+--------+------+ Basically I wish all non viewed rows to be selected by the statement, that is accomplished by checking weather the viewed column is true or false, pretty simple and straightforward, nothing to worry here. However when it comes to the rows already viewed, meaning the column viewed is TRUE, for those records I only want 3 rows to be returned for each group. The appropriate result in this instance should be the 3 most recent rows of each group. +----+------+-----+--------+------+ | id | from | to | viewed | data | +----+------+-----+--------+------+ | 6 | 10 | 1 | true | .... | | 7 | 8 | 6 | true | .... | | 8 | 10 | 1 | true | .... | | 9 | 6 | 8 | true | .... | | 10 | 2 | 3 | true | .... | | 11 | 1 | 10 | true | .... | | 12 | 8 | 6 | true | .... | +----+------+-----+--------+------+ As you see from the ideal result set we have three groups. Therefore the desired query for the viewed results should show a maximum of 3 rows for each grouping it finds. In this case these groupings were 10 with 1 and 8 with 6, both which had three rows to be shown, while the other group 2 with 3 only had one row to be shown. Please note that where from = x and to = y, makes the same grouping as if it was from = y and to = x. Therefore considering the first grouping (10 with 1), from = 10 and to = 1 is the same group if it was from = 1 and to = 10. However there are plenty of groups in the whole table that I only wish the 3 most recent of each to be returned in the select statement, and thats my problem, I not sure how that can be accomplished in the most efficient way possible considering the table will have hundreds if not thousands of records at some point. Thanks for your help. Note: The columns id, from, to and viewed are indexed, that should help with performance. PS: I'm unsure on how to name this question exactly, if you have a better idea, be my guest and edit the title.

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  • how to 'scale' these three tables?

    - by iddqd
    I have the following Tables: Players id playerName Weapons id type otherData Weapons2Player id playersID_reference weaponsID_reference That was nice and simple. Now I need to SELECT items from the Weapons table, according to some of their characteristics that i previously just packed into the otherData column (since it was only needed on the client side). The problem is, that the types have varying characteristics - but also a lot of similar data. So I'm trying to decide on the following possibilities, all of which have their pros and cons. Solution A Kill the Weapons table, and create a new table for each Weapon-Type: Weapons_Swords id bladeType damage otherData Weapons_Guns id accuracy damage ammoType otherData But how will i Link these to the Players ? create Weapons_Swords2Players, Weapons_Guns2Players for each weapon-type? (Will result in a lot more JOINS when loading the player with all his weapons...and it's also more complicated to insert a new player) or add another column to Weapons2Players called WeaponsTypeTable, then do sub-selects to the correct Weapons sub-table (seems easier, but not really right, slightly easier insert i guess) Solution B Keep the Weapons table, and add all the fields i need to it. The Problem is that then there will be NULL fields, since not all Weapon-Types use all fields (can't be right) Weapons id type accuracy damage ammoType bladeType otherData This seems to be pretty basic stuff, but i just can't decide what's best. Or is there a correct Solution C? many thanks.

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  • Foreign keys and pagination

    - by whitstone86
    This is my pagination script: <?php /*********************************** * PhpMyCoder Paginator * * Created By PhpMyCoder * * 2010 PhpMyCoder * * ------------------------------- * * You may use this code as long * * as this notice stays intact and * * the proper credit is given to * * the author. * ***********************************/ ?> <head> <title> Pagination Test - Created By PhpMyCoder</title> <style type="text/css"> #nav { font: normal 13px/14px Arial, Helvetica, sans-serif; margin: 2px 0; } #nav a { background: #EEE; border: 1px solid #DDD; color: #000080; padding: 1px 7px; text-decoration: none; } #nav strong { background: #000080; border: 1px solid #DDD; color: #FFF; font-weight: normal; padding: 1px 7px; } #nav span { background: #FFF; border: 1px solid #DDD; color: #999; padding: 1px 7px; } </style> </head> <?php //Require the file that contains the required classes include("pmcPagination.php"); //PhpMyCoder Paginator $paginator = new pmcPagination(20, "page"); //Connect to the database mysql_connect("localhost","root","PASSWORD"); //Select DB mysql_select_db("tvguide"); //Select only results for today and future $result = mysql_query("SELECT programme, channel, airdate, expiration, episode, setreminder FROM epdata1 where airdate >= now() order by expiration GROUP BY airdate"); //You can also add reuslts to paginate here mysql_data_seek($queryresult,0) ; while($row = mysql_fetch_array($result)) { $paginator->add(new paginationData($row['programme'], $row['channel'], $row['airdate'], $row['expiration'], $row['episode'], $row['setreminder'])); } ?> <?php //Show the paginated results $paginator->paginate (); ?><? include("pca-footer1.php"); ?> <?php //Show the navigation $paginator->navigation(); ?> However, I have two tables in this, and they are epdata1 (where the airtimes for my show House M.D. are) and housemdep plus the setreminder table. How can I use foreign keys in relation to this? I'm not sure if this will work for my script, but am willing to try. What I would like to do is to select certain episodes from the table housemdep (episodes of the show) and if any are selected it shows them as this: House M.D. showing on Channel 1 June 6th - 8:00pm "Wilson" Set Reminder House M.D. showing on Channel 1 June 7th - 1:30am "Wilson" Set Reminder House M.D. showing on Channel 1 June 7th - 12:55pm "House's Head" Set Reminder or like this, if I have not selected an episode from the row: House M.D. showing on Channel 1 June 7th - 8:00pm "House's Head" Set Reminder House M.D. showing on Channel 1 June 8th - 9:00pm Set Reminder House M.D. showing on Channel 1 June 9th - 2:30pm Set Reminder House M.D. showing on Channel 1 June 7th - 8:00pm "Que Sera Sera" Set Reminder Foreign keys and relationship of interlinked tables are new to me, if anyone could help I'd appreciate this. I've tried some of what Google suggested on foreign keys in another version of this script (this is a clone of the original on my localhost server running Apache and PHP 5.28/MySQL), but am not sure how to implement this. Thanks.

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  • filtering for multiple values on one column. All values must exist, else - return zero

    - by Andrew
    Hello All, I would like to filter one column in a table for couple values and show results only if all those values are there. If one or more is missing, then return zero results. example table +----+--------+----------+ | id | Fruit | Color | +----+--------+----------+ | 1 | apple | red | | 2 | mango | yellow | | 3 | banana | yellow | +----+--------+----------+ example "wrong" code: (this must return 3 rows) select Fruit FROM table WHERE Color = red AND Color = yellow but select Fruit FROM table WHERE Color = red AND Color = green must return 0 rows. (If i use select Fruit FROM table WHERE Color = red OR Color = green i get 1 row which is not what i need) I am using PHP with form where user checks different checkboxes that represent different values of the same column. So when he selects multiple checkboxes, all those values should be in the result set, otherwise no result should be given. Thank you, Andrew

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  • C# code for viewev tables

    - by simon
    Can somebody write me a code, how to view data from tables in c# (using select statement)? I tried it myself and posted the code here, but i didn't get it right. Please help!

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  • Java & Tomcat: SQL JDBC/JNDI Exceptions

    - by user267581
    I am deploying a webapp from eclipse to tomcat. I am having an issue with my application and JNDI lookups. When the app tries to load the JNDI resource I am this stacktrace: javax.naming.ServiceUnavailableException [Root exception is java.rmi.ConnectException: Connection refused to host: localhost; nested exception is: java.net.ConnectException: Connection refused: connect] at com.sun.jndi.rmi.registry.RegistryContext.lookup(RegistryContext.java:101) at javax.naming.InitialContext.lookup(InitialContext.java:396) at org.objectweb.carol.jndi.spi.AbsContext.lookup(AbsContext.java:134) at org.objectweb.carol.jndi.spi.AbsContext.lookup(AbsContext.java:144) at javax.naming.InitialContext.lookup(InitialContext.java:392) at org.objectweb.carol.jndi.spi.MultiContext.lookup(MultiContext.java:118) at javax.naming.InitialContext.lookup(InitialContext.java:392) at com.theriabook.daoflex.JDBCConnection.getDataSource(JDBCConnection.java:61) at com.theriabook.daoflex.JDBCConnection.getConnection(JDBCConnection.java:73) at com.aramark.data.UsersDAO.doLogin(UsersDAO.java:751) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at flex.messaging.services.remoting.adapters.JavaAdapter.invoke(JavaAdapter.java:406) at flex.messaging.services.RemotingService.serviceMessage(RemotingService.java:183) at flex.messaging.MessageBroker.routeMessageToService(MessageBroker.java:1417) at flex.messaging.endpoints.AbstractEndpoint.serviceMessage(AbstractEndpoint.java:878) at com.farata.remoting.CustomAMFEndpoint.serviceMessage(CustomAMFEndpoint.java:23) at flex.messaging.endpoints.amf.MessageBrokerFilter.invoke(MessageBrokerFilter.java:121) at flex.messaging.endpoints.amf.LegacyFilter.invoke(LegacyFilter.java:158) at flex.messaging.endpoints.amf.SessionFilter.invoke(SessionFilter.java:49) at flex.messaging.endpoints.amf.BatchProcessFilter.invoke(BatchProcessFilter.java:67) at flex.messaging.endpoints.amf.SerializationFilter.invoke(SerializationFilter.java:146) at flex.messaging.endpoints.BaseHTTPEndpoint.service(BaseHTTPEndpoint.java:274) at flex.messaging.MessageBrokerServlet.service(MessageBrokerServlet.java:377) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at com.cti.compiler.env.web.CompilerInvocationInterceptor.doFilter(CompilerInvocationInterceptor.java:25) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447) at java.lang.Thread.run(Thread.java:619) Caused by: java.rmi.ConnectException: Connection refused to host: localhost; nested exception is: java.net.ConnectException: Connection refused: connect at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:601) at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:198) at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:184) at sun.rmi.server.UnicastRef.newCall(UnicastRef.java:322) at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source) at com.sun.jndi.rmi.registry.RegistryContext.lookup(RegistryContext.java:97) ... 41 more Caused by: java.net.ConnectException: Connection refused: connect at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) at java.net.Socket.connect(Socket.java:525) at java.net.Socket.connect(Socket.java:475) at java.net.Socket.<init>(Socket.java:372) at java.net.Socket.<init>(Socket.java:186) at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:22) at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:128) at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:595) I am really stumped at this error. I am using a WinXP running on a Virtual Machine (VMWare) from a MAC. Any ideas? I have uninstalled/reinstalled tomcat multiple times.

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  • Why would I get a duplicate key error when updating a row?

    - by hdx
    I'm using postgres and I'm getting the duplicate key error when updating a row: cursor.execute("UPDATE jiveuser SET userenabled = 0 WHERE userid = %s" % str(userId)) psycopg2.IntegrityError: duplicate key value violates unique constraint "jiveuser_pk" I don't understand how updating a row can cause this error... any help will be much appreciated.

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  • SSRS report combine data sources and generate csv

    - by Nithin
    I am new to ssrs. I have a report that gets data from two databases. I can create two datasets that connect to two different databases. The databases are third party and I cannot create stored procedures on the databases. My issue is that I have to combine the data from the two queries. Please help me with this issue or point me to locations where I can find answers. Thanks in advance.

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  • LIKE operator with $variable

    - by skarama
    This is my first question here and I hope it is simple enough to get a quick answer! Basically, I have the following code: $variable = curPageURL(); $query = 'SELECT * FROM `tablename` WHERE `columnname` LIKE '$variable' ; If I echo the $variable, it prints the current page's url( which is a javascript on my page) Ultimately, what I want, is to be able to make a search for which the search-term is the current page's url, with wildcards before and after. I am not sure if this is possible at all, or if I simply have a syntax error, because I get no errors, simply no result! I tried : $query = 'SELECT * FROM `tablename` WHERE `columnname` LIKE '"echo $variable" ' ; But again, I'm probably missing or using a misplaced ' " ; etc. Please tell me what I'm doing wrong!

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  • How to call a scalar function in a stored procedure

    - by Luke101
    I am wacking y head over the problem with this code. DECLARE @root hierarchyid declare @lastchild hierarchyid SELECT @root = NodeHierarchyID from NodeHierarchy where ID = 1 set @lastchild = getlastchild(@root) it says it does not recognize getlastchild function. What am I doing wrong here

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  • How do I perform a batch insert in Django?

    - by Thierry Lam
    In mysql, you can insert multiple rows to a table in one query for n 0: INSERT INTO tbl_name (a,b,c) VALUES(1,2,3),(4,5,6),(7,8,9), ..., (n-2, n-1, n); Is there a way to achieve the above with Django queryset methods? Here's an example: values = [(1, 2, 3), (4, 5, 6), ...] for value in values: SomeModel.objects.create(first=value[0], second=value[1], third=value[2]) I believe the above is calling an insert query for each iteration of the for loop. I'm looking for a single query, is that possible in Django?

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  • Subquery max sequence number

    - by Andy Levesque
    I'm hesitant to ask because I'm sure it's out there, but I just can't seem to come up with the keywords to find the answer. I'm stepping outside my boundaries by starting with subqueries (normally an Access user). I have a query that has TECH_ID, SEQ_NBR, and PELL_FT_AWD_AMT SELECT ISRS_V_NEED_ANAL_RESULT_PARENT.TECH_ID, ISRS_V_NEED_ANAL_RESULT_PARENT.AWD_YR, ISRS_V_NEED_ANAL_RESULT_PARENT.PELL_FT_AWD_AMT, ISRS_V_NEED_ANAL_RESULT_PARENT.SEQ_NBR FROM ISRS_V_NEED_ANAL_RESULT_PARENT GROUP BY ISRS_V_NEED_ANAL_RESULT_PARENT.TECH_ID, ISRS_V_NEED_ANAL_RESULT_PARENT.AWD_YR, ISRS_V_NEED_ANAL_RESULT_PARENT.PELL_FT_AWD_AMT, ISRS_V_NEED_ANAL_RESULT_PARENT.SEQ_NBR HAVING (((ISRS_V_NEED_ANAL_RESULT_PARENT.AWD_YR)="2013")) ORDER BY ISRS_V_NEED_ANAL_RESULT_PARENT.TECH_ID; What I want to return is add a subquery that selects only the max SEQ_NUM for each record, but I can't seem to get the syntax right. In the past I would cheat and have a separate query that first gave me the TECH_ID and max SEQ_NUM, and then have a second query that use the original table and the first query in a join to get the rest. How can I do this in one query? Example: TECH_ID SEQ_NUM PELL 1 1 4000 1 2 4000 1 3 5000 Using just the max of the sequence number still returns: 1; 2; 4000 and 1; 3; 5000 when I'm only wanting the latter.

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  • Search select statement

    - by Nana
    I am creating a page which would have different field for the user to search from. e.g. search by: Grade: -dropdownlist1- Student name: -dropdownlist2- Student ID: -dropdownlist3- Lessons: -dropdownlist4- Year: -dropdownlist5- How do I write the select statement for this? Each dropdownlist would need a select statement which would extract out different data from the database. But, I want to write ONE select statement which can dynamically choose the dropdownlist options. Instead of writing many many select statement. Lets say; Grade: -dropdownlist1- ; default value(all) Student name: -dropdownlist2-; default value(all) Student ID: -dropdownlist3-; 0-100 is choosen Lessons: -dropdownlist4-; A-C is choosen Year: -dropdownlist5-; 2009 is choosen

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  • Sharepoint SSRS: Unexpected Error Encountered

    - by Nicholas
    We are running an intranet website hosted on Sharepoint 2007, serving reports to users via SSRS. Recently, our users are experiencing error when trying to access certain reports with the error message "An unexpected error has occurred". After trying many things, to cut a long story short we manage to temporarily solve the problem by manually running UPDATE STATISTICS on the tables in the database. However, this error will periodically crop up again and again, running UPDATE STATISTICS immediately solved it. I had suggested to run a daily job in the server to auto run UPDATE STATISTICS every few hours or so but was rejected by my team lead. Is there any other workaround for this error? Why does UPDATE STATISTICS solve the problem, I still not very understand?

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  • Date arithmetic using integer values

    - by Dave Jarvis
    Problem String concatenation is slowing down a query: date(extract(YEAR FROM m.taken)||'-1-1') d1, date(extract(YEAR FROM m.taken)||'-1-31') d2 This is realized in code as part of a string, which follows (where the p_ variables are integers): date(extract(YEAR FROM m.taken)||''-'||p_month1||'-'||p_day1||''') d1, date(extract(YEAR FROM m.taken)||''-'||p_month2||'-'||p_day2||''') d2 This part of the query runs in 3.2 seconds with the dates, and 1.5 seconds without, leading me to believe there is ample room for improvement. Question What is a better way to create the date (presumably without concatenation)? Many thanks!

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  • MySQL table data transformation -- how can I dis-aggregate MySQL time data?

    - by lighthouse65
    We are coding for a MySQL data warehousing application that stores descriptive data (User ID, Work ID, Machine ID, Start and End Time columns in the first table below) associated with time and production quantity data (Output and Time columns in the first table below) upon which aggregate (SUM, COUNT, AVG) functions are applied. We now wish to dis-aggregate time data for another type of analysis. Our current data table design: +---------+---------+------------+---------------------+---------------------+--------+------+ | User ID | Work ID | Machine ID | Event Start Time | Event End Time | Output | Time | +---------+---------+------------+---------------------+---------------------+--------+------+ | 080025 | ABC123 | M01 | 2008-01-24 16:19:15 | 2008-01-24 16:34:45 | 2120 | 930 | +---------+---------+------------+---------------------+---------------------+--------+------+ Reprocessing dis-aggregation that we would like to do would be to transform table content based on a granularity of minutes, rather than the current production event ("Event Start Time" and "Event End Time") granularity. The resulting reprocessing of existing table rows would look like: +---------+---------+------------+---------------------+--------+ | User ID | Work ID | Machine ID | Production Minute | Output | +---------+---------+------------+---------------------+--------+ | 080025 | ABC123 | M01 | 2010-01-24 16:19 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:20 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:21 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:22 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:23 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:24 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:25 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:26 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:27 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:28 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:29 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:30 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:31 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:22 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:33 | 133 | | 080025 | ABC123 | M01 | 2010-01-24 16:34 | 133 | +---------+---------+------------+---------------------+--------+ So the reprocessing would take an existing row of data created at the granularity of production event and modify the granularity to minutes, eliminating redundant (Event End Time, Time) columns while doing so. It assumes a constant rate of production and divides output by the difference in minutes plus one to populate the new table's Output column. I know this can be done in code...but can it be done entirely in a MySQL insert statement (or otherwise entirely in MySQL)? I am thinking of a INSERT ... INTO construction but keep getting stuck. An additional complexity is that there are hundreds of machines to include in the operation so there will be multiple rows (one for each machine) for each minute of the day. Any ideas would be much appreciated. Thanks.

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  • Get sum of two columns in one LINQ query

    - by Axarydax
    Hi, let's say that I have a table called Items (ID int, Done int, Total int) I can do it by two queries: int total = m.Items.Sum(p=>p.Total) int done = m.Items.Sum(p=>p.Done) But I'd like to do it in one query, something like this: var x = from p in m.Items select new { Sum(p.Total), Sum(p.Done)}; Surely there is a way to call aggregate functions from LINQ syntax...?

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  • Query not returning rows in a table that don't have corresponding values in another [associative] ta

    - by Obay
    I have Table: ARTICLES ID | CONTENT --------------- 1 | the quick 2 | brown fox 3 | jumps over 4 | the lazy Table: WRITERS ID | NAME ---------- 1 | paul 2 | mike 3 | andy Table: ARTICLES_TO_WRITERS ARTICLE_ID | WRITER_ID ----------------------- 1 | 1 2 | 2 3 | 3 To summarize, article 4 has no writer. So when I do a "search" for articles with the word "the": SELECT a.id, a.content, w.name FROM articles a, writers w, articles_to_writers atw WHERE a.id=atw.article_id AND w.id=atw.writer_id AND content LIKE '%the%' article 4 does not show up in the result: ID | CONTENT | NAME ----------------------- 1 | the quick | paul How do I make article 4 still appear in the results even though it has no writers?

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  • mysql query - blog posts and comments with limit

    - by Lemon
    Hi, I have 2 tables: comments and posts and I'd like to display a list of 15 posts and maximum 2 most recent comments under each blog post the database scheme looks like this posts_table: post_id, post_txt, post_timestamp comments_table: post_id, comment_txt, comment_timestamp how the mysql query should look like to select 15 posts and related comments (max 2 most recent ones per post) ??? thanks, Leo

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  • Python: Retrieve Image from MSSQL

    - by KoRkOnY
    Dear All, I'm working on a Python project that retrieves an image from MSSQL. My code is able to retrieve the images successfully but with a fixed size of 63KB. if the image is greater than that size, it just brings the first 63KB from the image! The following is my code: #!/usr/bin/python import _mssql mssql=_mssql.connect('<ServerIP>','<UserID>','<Password>') mssql.select_db('<Database>') x=1 while x==1: query="select TOP 1 * from table;" if mssql.query(query): rows=mssql.fetch_array() rowNumbers = rows[0][1] #print "Number of rows fetched: " + str(rowNumbers) for row in rows: for i in range(rowNumbers): FILE=open('/home/images/' + str(row[2][i][1]) + '-' + str(row[2][i][2]).strip() + ' (' + str(row[2][i][0]) + ').jpg','wb') FILE.write(row[2][i][4]) FILE.close() print 'Successfully downloaded image: ' + str(row[2][i][0]) + '\t' + str(row[2][i][2]).strip() + '\t' + str(row[2][i][1]) else: print mssql.errmsg() print mssql.stdmsg() mssql.close()

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  • MySQL MyISAM table performance... painfully, painfully slow

    - by Salman A
    I've got a table structure that can be summarized as follows: pagegroup * pagegroupid * name has 3600 rows page * pageid * pagegroupid * data references pagegroup; has 10000 rows; can have anything between 1-700 rows per pagegroup; the data column is of type mediumtext and the column contains 100k - 200kbytes data per row userdata * userdataid * pageid * column1 * column2 * column9 references page; has about 300,000 rows; can have about 1-50 rows per page The above structure is pretty straight forwad, the problem is that that a join from userdata to page group is terribly, terribly slow even though I have indexed all columns that should be indexed. The time needed to run a query for such a join (userdata inner_join page inner_join pagegroup) exceeds 3 minutes. This is terribly slow considering the fact that I am not selecting the data column at all. Example of the query that takes too long: SELECT userdata.column1, pagegroup.name FROM userdata INNER JOIN page USING( pageid ) INNER JOIN pagegroup USING( pagegroupid ) Please help by explaining why does it take so long and what can i do to make it faster. Edit #1 Explain returns following gibberish: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE userdata ALL pageid 372420 1 SIMPLE page eq_ref PRIMARY,pagegroupid PRIMARY 4 topsecret.userdata.pageid 1 1 SIMPLE pagegroup eq_ref PRIMARY PRIMARY 4 topsecret.page.pagegroupid 1 Edit #2 SELECT u.field2, p.pageid FROM userdata u INNER JOIN page p ON u.pageid = p.pageid; /* 0.07 sec execution, 6.05 sec fecth */ id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE u ALL pageid 372420 1 SIMPLE p eq_ref PRIMARY PRIMARY 4 topsecret.u.pageid 1 Using index SELECT p.pageid, g.pagegroupid FROM page p INNER JOIN pagegroup g ON p.pagegroupid = g.pagegroupid; /* 9.37 sec execution, 60.0 sec fetch */ id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE g index PRIMARY PRIMARY 4 3646 Using index 1 SIMPLE p ref pagegroupid pagegroupid 5 topsecret.g.pagegroupid 3 Using where Moral of the story Keep medium/long text columns in a separate table if you run into performance problems such as this one.

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