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  • Can in-memory SQLite databases scale with concurrency?

    - by Kent Boogaart
    In order to prevent a SQLite in-memory database from being cleaned up, one must use the same connection to access the database. However, using the same connection causes SQLite to synchronize access to the database. Thus, if I have many threads performing reads against an in-memory database, it is slower on a multi-core machine than the exact same code running against a file-backed database. Is there any way to get the best of both worlds? That is, an in-memory database that permits multiple, concurrent calls to the database?

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  • Is there an alternative to Microsoft.SqlServer.Management.Smo.SqlDataType that includes a value for

    - by Daniel Schaffer
    The Microsoft.SqlServer.Management.Smo.SqlDataType enum has a value for the timestamp type but not rowversion. I'm looking for an updated version of the assembly or an alternate enum type that supports it. The existing enum has a value for Timestamp, but according to the rowversion documentation, timestamp is "deprecated and will be removed in a future version". I prefer to avoid using deprecated things :)

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  • Parse both symbols . and , as decimal digits delimiter in ASP.NET

    - by abatishchev
    I'm writing a banking system and my customer wants support both Russian and American numeric standards in decimal digits delimiter. Respectively . and ,. Now only , works properly. Perhaps because of web server's OS format (Russian is set). String like 2000.00 throws a FormatException: Input string was not in a correct format. How to fix that? Are there any other ideas except String.Replace('.', ',') on FormView.ItemInserting event?

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  • alter mysqldump file before import

    - by julio
    Hi-- I have a mysqldump file created from an earlier version of a product that can't be imported into a new version of the product, since the db structure has changed slightly (mainly altering a column that was NOT NULL DEFAULT 0 to UNIQUE KEY DEFAULT NULL). If I just import the old dump file, it will error out since the column that has default values of 0 now breaks the UNIQUE constraint. It would be easy enough to either manually alter the mysqldump file, or import into a temp table and change it, then copy to the new table. However, is there a way to do this programatically, so it will be repeatable and not manual? (this will need to happen for many instances of this product). I'm thinking something like disabling key constraints for the import, then setting all values that = 0 to NULL, then re-enabling the key constraints? Is this possible? Any help appreciated.

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  • MySQL: Efficient Blobbing?

    - by feklee
    I'm dealing with blobs of up to - I estimate - about 100 kilo bytes in size. The data is compressed already. Storage engine: InnoDB on MySQL 5.1 Frontend: PHP (Symfony with Propel ORM) Some questions: I've read somewhere that it's not good to update blobs, because it leads to reallocation, fragmentation, and thus bad performance. Is that true? Any reference on this? Initially the blobs get constructed by appending data chunks. Each chunk is up to 16 kilo bytes in size. Is it more efficient to use a separate chunk table instead, for example with fields as below? parent_id, position, chunk Then, to get the entire blob, one would do something like: SELECT GROUP_CONCAT(chunk ORDER BY position) FROM chunks WHERE parent_id = 187 The result would be used in a PHP script. Is there any difference between the types of blobs, aside from the size needed for meta data, which should be negligible.

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  • T-SQL Query, combine columns from multiple rows into single column

    - by Shayne
    I have seeen some examples of what I am trying to do using COALESCE and FOR XML (seems like the better solution). I just can't quite get the syntax right. Here is what I have (I will shorten the fields to only the key ones): Table Fields ------ ------------------------------- Requisition ID, Number IssuedPO ID, Number Job ID, Number Job_Activity ID, JobID (fkey) RequisitionItems ID, RequisitionID(fkey), IssuedPOID(fkey), Job_ActivityID (fkey) I need a query that will list ONE Requisition per line with its associated Jobs and IssuedPOs. (The requisition number start with "R-" and the Job Number start with "J-"). Example: R-123 | "PO1; PO2; PO3" | "J-12345; J-6780" Sure thing Adam! Here is a query that returns multiple rows. I have to use outer joins, since not all Requisitions have RequisitionItems that are assigned to Jobs and/or IssuedPOs (in that case their fkey IDs would just be null of course). SELECT DISTINCT Requisition.Number, IssuedPO.Number, Job.Number FROM Requisition INNER JOIN RequisitionItem on RequisitionItem.RequisitionID = Requisition.ID LEFT OUTER JOIN Job_Activity on RequisitionItem.JobActivityID = Job_Activity.ID LEFT OUTER JOIN Job on Job_Activity.JobID = Job.ID LEFT OUTER JOIN IssuedPO on RequisitionItem.IssuedPOID = IssuedPO.ID

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  • Why are joins bad when considering scalability?

    - by acidzombie24
    Why are joins bad or 'slow'. I know i heard this more then once. I found this quote The problem is joins are relatively slow, especially over very large data sets, and if they are slow your website is slow. It takes a long time to get all those separate bits of information off disk and put them all together again. source I always thought they were fast especially when looking up a PK. Why are they 'slow'?

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  • Conditional SELECT MySQL

    - by user188693
    Don't know if this is possible, but I'd like to select records based on the field value of recur_type, where the 'm' is the day of the week. If it's a weekly recurring event, I need to make sure this is a day it recurs on, otherwise, I want to return all days. however, I'm getting an empty result set: SELECT * FROM wp_fun_bec_events WHERE start_date <= '2009-10-12' AND ( end_date >= '2009-10-12' OR (recur_end > '0' AND recur_end >= '2009-10-12' ) ) AND ('m' IN ( CASE WHEN 'recur_type' = 'weekly' THEN recur_days ELSE 's/m/t/w/r/f/a' END ) ) ORDER BY start_date, start_time Any ideas??

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  • Proper way to structure a Sync Framework DAL

    - by Refracted Paladin
    I am creating a WPF app that needs to allow users to work in a temporary disconnected state and I plan to use a Local Database Cache. My question's are about my data access layer. Do you typically create the whole DAL to point at the Cache or both and create a switching mechanism? Is Entity's a good way to go for my DAL against the Cache? I am used to L2S but my understanding is that I can't use that against SQLCE, correct? Thanks! PS: Any good resources out there for using Sync, Linq, and WPF ALL TOGETHER? Tutorials, videos, etc?

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  • How to apply GROUP_CONCAT in mysql Query

    - by Query Master
    How to apply GROUP_CONCAT in this Query if you guys have any idea or any alternate solution about this please share me. Helps are definitely appreciated also (see Query or result required) Query SELECT WEEK(cpd.added_date) AS week_no,COUNT(cpd.result) AS death_count FROM cron_players_data cpd WHERE cpd.player_id = 81 AND cpd.result = 2 AND cpd.status = 1 GROUP BY WEEK(cpd.added_date); Query output result screen Result Required 23,24,25 AS week_no 2,3,1 AS death_count

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  • Listing issue, GROUP mysql

    - by SethCodes
    Here is a mock-up example of Mysql table: | ID | Country | City | ________________________________ | 1 | Sweden | Stockholm | | 2 | Sweden | Stockholm | | 3 | Sweden | Lund | | 4 | Sweden | Lund | | 5 | Germany | Berlin | | 6 | Germany | Berlin | | 7 | Germany | Hamburg | | 8 | Germany | Hamburg | Notice how both rows Country and city have repeated values inside them. Using GROUP BY country, city in my PDO query, the values will not repeat while in loop. Here is PDO for this: $query = "SELECT id, city, country FROM table GROUP BY country, city"; $stmt = $db->query($query); while($row = $stmt->fetch(PDO::FETCH_ASSOC)) : The above code will result in an output like this (some editing in-between). GROUP BY works but the country repeats: Sweden - Stockholm Sweden - Lund Germany - Berlin Germany - Hamburg Using bootstrap collapse and above code, I separate the country from the city with a simple drop down collopase. Here is code: <li> <a data-toggle="collapse" data-target="#<?= $row['id']; ?>" href="search.php?country=<?= $row['country']; ?>"> <?= $row['country']; ?> </a> <div id ="<?= $row['id']; ?>" class="collapse in"> //collapse div here <a href="search.php?city=<?= $row['city']; ?>"> <?= $row['city']; ?><br></a> </div> //end </li> It then looks something like this (once collapse is initiated): Sweden > Stockholm Sweden > Lund Germany >Berlin Germany >Hamburg Here is where I face the problem. The above lists the values Sweden and Germany 2 times. I want Sweden and Germany to only list one time, and the cities listed below, so the desired look is to be this: Sweden // Lists one time > Stockholm > Lund Germany // Lists one time >Berlin >Hamburg I have tried using DISTINCT, GROUP_CONTACT and other methods, yet none get my desired output (above). Suggestions? Below is my current full code in action: <? $query = "SELECT id, city, country FROM table GROUP BY country, city"; $stmt = $db->query($query); while($row = $stmt->fetch(PDO::FETCH_ASSOC)) : ?> <li> <a data-toggle="collapse" data-target="#<?= $row['id']; ?>" href="search.php?country=<?= $row['country']; ?>"> <?= $row['country']; ?> </a> <div id ="<?= $row['id']; ?>" class="collapse in"> //collapse div here <a href="search.php?city=<?= $row['city']; ?>"> <?= $row['city']; ?><br></a> </div> //end </li> <? endwhile ?>

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  • Calculate open timeslots given availability and existing appointments - by day

    - by Andre
    Overview: I have a table which stores a persons "availability" for a current day, e.g. Mon - 8:00am - 11:30am Mon - 1:30pm - 6:00pm A second table stores appointments that this person already has for the same day, e.g. Mon - 8:30am - 11:00am Mon - 2:30pm - 4pm Desired result: Doing calculationsI'd like to have the following result - e.g. "this person has availability on the given day": Mon - 8:00am - 8:30am Mon - 11:00am - 11:30am Mon - 1:30pm - 2:30pm Mon - 4:00pm - 6:00pm Any ideas on how to calculate the output given the two inputs (e.g. availability, existing appointments) would be greatly appreciated. Preferably I'd use javascript on the client to do the calculating as I would believe that doing it within the DB (I'm using MSSQL) would be slow for many records, persons, etc. Hope this is enough information to illustrate the problem at hand - Many thanks in advance.

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  • How to retrieve last primary Id from mdb's table?

    - by William
    I got table with next columns: Id, Name, Age, Class I am trying to insert new row in db like this: INSERT INTO MyTable (Name, Age, Class) VALUES (@name, @age, @class) And get an exeption: "Index or primary key cannot contain a Null value." The question is how to add a new row without knowing next primary Id, or maybe there is a way to get this Id from the table with the help of another query ?

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  • Right way to implement a n-to-m related

    - by ThreeFingerMark
    Hello, this is a part from my database structure: Table: Item Columns: ItemID, Title, Content, Price Table: Tag Columns: TagID, Title Table: ItemTag Columns: ItemID, TagID Table: Image Columns: ImageID, Path, Size, UploadDate Table: ItemImage Columns: ItemID, ImageID The items can have more than one image so i have a extra table "Image" and map this images to an items. I see now a problem with this structure. Before i can add Images i must enter an item. My question is now. Is this structure a good way to solve my problem with many images / tags for one item? Thank you

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  • Data historian queries

    - by Scott Dennis
    Hi, I have a table that contains data for electric motors the format is: DATE(DateTime) | TagName(VarChar(50) | Val(Float) | 2009-11-03 17:44:13.000 | Motor_1 | 123.45 2009-11-04 17:44:13.000 | Motor_1 | 124.45 2009-11-05 17:44:13.000 | Motor_1 | 125.45 2009-11-03 17:44:13.000 | Motor_2 | 223.45 2009-11-04 17:44:13.000 | Motor_2 | 224.45 Data for each motor is inserted daily, so there would be 31 Motor_1s and 31 Motor_2s etc. We do this so we can trend it on our control system displays. I am using views to extract last months max val and last months min val. Same for this months data. Then I join the two and calculate the difference to get the actual run hours for that month. The "Val" is a nonresetable Accumulation from a PLC(Controller). This is my query for Last months Max Value: SELECT TagName, Val AS Hours FROM dbo.All_Data_From_Last_Mon AS cur WHERE (NOT EXISTS (SELECT TagName, Val FROM dbo.All_Data_From_Last_Mon AS high WHERE (TagName = cur.TagName) AND (Val > cur.Val))) This is my query for Last months Max Value: SELECT TagName, Val AS Hours FROM dbo.All_Data_From_Last_Mon AS cur WHERE (NOT EXISTS (SELECT TagName, Val FROM dbo.All_Data_From_Last_Mon AS high WHERE (TagName = cur.TagName) AND (Val < cur.Val))) This is the query that calculates the difference and runs a bit slow: SELECT dbo.Motors_Last_Mon_Max.TagName, STR(dbo.Motors_Last_Mon_Max.Hours - dbo.Motors_Last_Mon_Min.Hours, 12, 2) AS Hours FROM dbo.Motors_Last_Mon_Min RIGHT OUTER JOIN dbo.Motors_Last_Mon_Max ON dbo.Motors_Last_Mon_Min.TagName = dbo.Motors_Last_Mon_Max.TagName I know there is a better way. Ultimately I just need last months total and this months total. Any help would be appreciated. Thanks in advance

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  • oracle search word in string

    - by Atul
    I want to search a word in string in ORACLE in which string is comma separated. Eg. String is ('MF1,MF2,MF3') and now I want to search whether 'MF' exists in that or not. If I am using instr('MF1,MF2,MF3','MF') it will give wrong result since I want to search Full MF in MF1 or MF2 or MF3.

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  • mysql replace matching but not changing

    - by alex
    I've used mysql's update replace function before, but even though I think I'm following the same syntax, I can't get this to work-it matches the rows, but doesn't replace. Here's what I'm trying to do: mysql> update contained_widgets set preference_values = replace(preference_values, '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li>', '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li> <li> <a_href="/projects"><span class="not-tc">Projects</span></a></li>'); Query OK, 0 rows affected (0.00 sec) Rows matched: 77 Changed: 0 Warnings: 0 I don't see what I'm missing. Any help is appreciated. I edited "a " to "a_" because the site thinks I'm posting spam links otherwise.

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  • Android quotes within an sql query string

    - by miannelle
    I want to perform a query like the following: uvalue = EditText( some user value ); p_query = "select * from mytable where name_field = '" + uvalue + "'" ; mDb.rawQuery( p_query, null ); if the user enters a single quote in their input it crashes. If you change it to: p_query = "select * from mytable where name_field = \"" + uvalue + "\"" ; it crashes if the user enters a double quote in their input. and of course they could always enter both single and double quotes.

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  • Advanced queries in HBase

    - by Teflon Ted
    Given the following HBase schema scenario (from the official FAQ)... How would you design an Hbase table for many-to-many association between two entities, for example Student and Course? I would define two tables: Student: student id student data (name, address, ...) courses (use course ids as column qualifiers here) Course: course id course data (name, syllabus, ...) students (use student ids as column qualifiers here) This schema gives you fast access to the queries, show all classes for a student (student table, courses family), or all students for a class (courses table, students family). How would you satisfy the request: "Give me all the students that share at least two courses in common"? Can you build a "query" in HBase that will return that set, or do you have to retrieve all the pertinent data and crunch it yourself in code?

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