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  • Deleting partial data from a field in MySQL

    - by Graham
    I am trying to remove a specific set of data from a MySQL database field, however I am not sure what the best statement would be for this. For example, if I have a data in a field such as... The use of a secondary password will allow you to gain access to your account from a non-authenticated computer. A non-authenticated computer is any computer that is not your primary computer, an elected authenticated computer or a computer that automatically deletes cookies. <p>This is a test</p> ...and I want to remove <p>This is a test</p> from the field, what statement would be best?

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  • Does Table.InsertOnSubmit create a copy of the original table?

    - by Bryan
    Using InsertOnSubmit seems to have some memory overhead. I have a System.Data.Linq.Table<User> table. When I do table.InsertOnSubmit(user) and then int count = table.Count(), the memory usage of my application increases by roughly the size of the User table, but the count is the number of items before user was inserted. So I'm guess an enumeration after InsertOnSubmit will create a copy of the table. Is that true?

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  • Check for active connection in NHibernate

    - by Dofs
    I have a system with a few different databases, and I would like to check if a certain database is down, and if so display a message to the user. Is it possible in NHibernate to check if there is an active connection to the database, without having to request data and then catch the exception?

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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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  • sql data source

    - by George
    I have a table (EmployeeID,EmployeeName,ManagerID) How can I create a sqldatasource to include the ManagerName from the EmployeeName given EmployeeID = ManagerID? In my gridview after dragging a dropdownlist what bindings should I do to display the managerName? Is it possible to use it without writing custom select,insert,delete,update? If not what are the steps I need to do to write the whole thing i.e. custom grid and source? Thank you very much

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  • MySQL: Question about SELECT WHERE AND/OR

    - by Andrew
    I'm trying to write a query that returns the same result from three different events, but I think I am doing it wrong. I can run my query against one event ID and it works. How can I select all three? Here's what I have so far: SELECT * FROM `Registrations` WHERE `Role` = "Attendee" AND `RegistrationStatus_ID` = "1" AND `DigSignature` IS NULL AND `Event_ID` = "147" OR `Event_ID` = "155" OR `Event_ID` = "160"

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  • Table for each region in MySQL

    - by King Wu
    There are four regions with more than one million records total. Should I create a table with a region column or a table for each region and combine them to get the top ranks? If I combine all four regions, none of my columns will be unique so I will need to also add an id column for my primary key. Otherwise, name, accountId & characterId would be candidate keys or should I just add an id column anyways. Table: ---------------------------------------------------------------- | name | accountId | iconId | level | characterId | updateDate | ----------------------------------------------------------------

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  • Advice on Linq to SQL mapping object design

    - by fearofawhackplanet
    I hope the title and following text are clear, I'm not very familiar with the correct terms so please correct me if I get anything wrong. I'm using Linq ORM for the first time and am wondering how to address the following. Say I have two DB tables: User ---- Id Name Phone ----- Id UserId Model The Linq code generator produces a bunch of entity classes. I then write my own classes and interfaces which wrap these Linq classes: class DatabaseUser : IUser { public DatabaseUser(User user) { _user = user; } public Guid Id { get { return _user.Id; } } ... etc } so far so good. Now it's easy enough to find a users phones from Phones.Where(p => p.User = user) but surely comsumers of the API shouldn't need to be writing their own Linq queries to get at data, so I should wrap this query in a function or property somewhere. So the question is, in this example, would you add a Phones property to IUser or not? In other words, should my interface specifically be modelling my database objects (in which case Phones doesn't belong in IUser), or are they actually simply providing a set of functions and properties which are conceptually associated with a User (in which case it does)? There seems drawbacks to both views, but I'm wondering if there is a standard approach to the problem. Or just any general words of wisdom you could share. My first thought was to use extension methods but in fact that doesn't work in this case.

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  • Can MySQL reasonably perform queries on billions of rows?

    - by haxney
    I am planning on storing scans from a mass spectrometer in a MySQL database and would like to know whether storing and analyzing this amount of data is remotely feasible. I know performance varies wildly depending on the environment, but I'm looking for the rough order of magnitude: will queries take 5 days or 5 milliseconds? Input format Each input file contains a single run of the spectrometer; each run is comprised of a set of scans, and each scan has an ordered array of datapoints. There is a bit of metadata, but the majority of the file is comprised of arrays 32- or 64-bit ints or floats. Host system |----------------+-------------------------------| | OS | Windows 2008 64-bit | | MySQL version | 5.5.24 (x86_64) | | CPU | 2x Xeon E5420 (8 cores total) | | RAM | 8GB | | SSD filesystem | 500 GiB | | HDD RAID | 12 TiB | |----------------+-------------------------------| There are some other services running on the server using negligible processor time. File statistics |------------------+--------------| | number of files | ~16,000 | | total size | 1.3 TiB | | min size | 0 bytes | | max size | 12 GiB | | mean | 800 MiB | | median | 500 MiB | | total datapoints | ~200 billion | |------------------+--------------| The total number of datapoints is a very rough estimate. Proposed schema I'm planning on doing things "right" (i.e. normalizing the data like crazy) and so would have a runs table, a spectra table with a foreign key to runs, and a datapoints table with a foreign key to spectra. The 200 Billion datapoint question I am going to be analyzing across multiple spectra and possibly even multiple runs, resulting in queries which could touch millions of rows. Assuming I index everything properly (which is a topic for another question) and am not trying to shuffle hundreds of MiB across the network, is it remotely plausible for MySQL to handle this? UPDATE: additional info The scan data will be coming from files in the XML-based mzML format. The meat of this format is in the <binaryDataArrayList> elements where the data is stored. Each scan produces = 2 <binaryDataArray> elements which, taken together, form a 2-dimensional (or more) array of the form [[123.456, 234.567, ...], ...]. These data are write-once, so update performance and transaction safety are not concerns. My naïve plan for a database schema is: runs table | column name | type | |-------------+-------------| | id | PRIMARY KEY | | start_time | TIMESTAMP | | name | VARCHAR | |-------------+-------------| spectra table | column name | type | |----------------+-------------| | id | PRIMARY KEY | | name | VARCHAR | | index | INT | | spectrum_type | INT | | representation | INT | | run_id | FOREIGN KEY | |----------------+-------------| datapoints table | column name | type | |-------------+-------------| | id | PRIMARY KEY | | spectrum_id | FOREIGN KEY | | mz | DOUBLE | | num_counts | DOUBLE | | index | INT | |-------------+-------------| Is this reasonable?

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  • Password security; Is this safe?

    - by Camran
    I asked a question yesterday about password safety... I am new at security... I am using a mysql db, and need to store users passwords there. I have been told in answers that hashing and THEN saving the HASHED value of the password is the correct way of doing this. So basically I want to verify with you guys this is correct now. It is a classifieds website, and for each classified the user puts, he has to enter a password so that he/she can remove the classified using that password later on (when product is sold for example). In a file called "put_ad.php" I use the $_POST method to fetch the pass from a form. Then I hash it and put it into a mysql table. Then whenever the users wants to delete the ad, I check the entered password by hashing it and comparing the hashed value of the entered passw against the hashed value in the mysql db, right? BUT, what if I as an admin want to delete a classified, is there a method to "Unhash" the password easily? sha1 is used currently btw. some code is very much appreciated. Thanks

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  • How to 'insert if not exists' in MySQL?

    - by warren
    I started by googling, and found this article which talks about mutex tables. I have a table with ~14 million records. If I want to add more data in the same format, is there a way to ensure the record I want to insert does not already exist without using a pair of queries (ie, one query to check and one to insert is the result set is empty)? Does a unique constraint on a field guarantee the insert will fail if it's already there? It seems that with merely a constraint, when I issue the insert via php, the script croaks.

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  • mysql count rows and grop them by month

    - by user2661296
    I have a table called cc_calls and there I have many call records I want to count them and group them in months I have a timestamp called starttime and I can use that row to extract the month, also limit the count for 12 months the results should be like: Month Count January 768768 February 876786 March 987979 April 765765 May 898797 June 876876 July 786575 August 765765 September 689787 October 765879 November 897989 December 876876 Can anyone guide me or show me the mysql query that I need to get this result.

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  • Database concurrency issue in .NET application

    - by MC.
    If userA deleted OrderA while userB is modifying OrderA, then userB saves OrderA then there is no order in the database to be updated. My problem is there is no error! The SqlDataAdapter.Update succeeds and returns a "1" indicating a record was modified when this is not true. Does anybody know how this is supposed to work, thanks.

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  • Updating database row from model

    - by Jamie Dixon
    Hey everyone, I'm haing a few problems updating a row in my database using Linq2Sql. Inside of my model I have two methods for updating and saving from my controller, which in turn receives an updated model from my view. My model methods like like: public void Update(Activity activity) { _db.Activities.InsertOnSubmit(activity); } public void Save() { _db.SubmitChanges(); } and the code in my Controller likes like: [HttpPost] public ActionResult Edit(Activity activity) { if (ModelState.IsValid) { UpdateModel<Activity>(activity); _activitiesModel.Update(activity); _activitiesModel.Save(); } return View(activity); } The problem I'm having is that this code inserts a new entry into the database, even though the model item i'm inserting-on-submit contains a primary key field. I've also tried re-attaching the model object back to the data source but this throws an error because the item already exists. Any pointers in the right direction will be greatly appreciated. UPDATE: I'm using dependancy injection to instantiate my datacontext object as follows: IMyDataContext _db; public ActivitiesModel(IMyDataContext db) { _db = db; }

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  • (NOT) NULL for NVARCHAR columns

    - by Anders Abel
    Allowing NULL values on a column is normally done to allow the absense of a value to be represented. When using NVARCHAR there is aldready a possibility to have an empty string, without setting the column to NULL. In most cases I cannot see a semantical difference between an NVARCHAR with an empty string and a NULL value for such a column. Setting the column as NOT NULL saves me from having to deal with the possibility of NULL values in the code and it feels better to not have to different representations of "no value" (NULL or an empty string). Will I run into any other problems by setting my NVARCHAR columns to NOT NULL. Performance? Storage size? Anything I've overlooked on the usage of the values in the client code?

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  • slow record deletion with large ntext values

    - by asking
    I'm having trouble deleting some records via a stored procedure from a table in SQLServer 2008R2 that has ntext columns. The stored proc is timing out and running the query directly takes a very long time. The initial query was a straight "delete from y where x = z" and I've also tried running it in batches of 1000 with transactions but it is still slow and timing out in a stored proc. The majority of the records in the table will not be deleted each time (it's not just a once-off query but will be run other times). The ntext columns are not used in the where clause and I can't change the column types. Any suggestions on the quickest way to delete records with large ntext values? Thanks

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  • How to do this query?

    - by Damiano
    Hello everybody! I have a mysql table with these columns: ID (auto-increment) ID_BOOK (int) PRICE (double) DATA (date) I know two ID_BOOK values, example, 1 and 2. QUERY: I have to extract all the PRICE (of the ID_BOOK=1 and ID_BOOK=2) where DATA is the same! Table example: 1 1 10.00 2010-05-16 2 1 11.00 2010-05-15 3 1 12.00 2010-05-14 4 2 18.00 2010-05-16 5 2 11.50 2010-05-15 Result example: 1 1 10.00 2010-05-16 4 2 18.00 2010-05-16 2 1 11.00 2010-05-15 5 2 11.50 2010-05-15 ID_BOOK=2 hasn't 2010-05-14 so i jump it. Thank you so much!

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  • Can I have a CASE statement within a WHILE loop?

    - by John
    This is what I'm doing: while (@counter < 3 and @newBalance >0) begin CASE when @counter = 1 then ( @monFee1 = @monthlyFee, @newBalance = @newBalance-@fee) when @counter = 2 then ( @monFee2 = @monthlyFee, @newBalance = @newBalance-@fee) END @counter = @counter +1 end I get this error: Incorrect syntax near the keyword 'CASE'. No idea why. Please help!

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  • Select 2 Rows from Table when COUNT of another table

    - by Marcus
    Here is the code that I currently have: SELECT `A`.* FROM `A` LEFT JOIN `B` ON `A`.`A_id` = `B`.`value_1` WHERE `B`.`value_2` IS NULL AND `B`.`userid` IS NULL ORDER BY RAND() LIMIT 2 What it currently is supposed to do is select 2 rows from A when the 2 rows A_id being selected are not in value_1 or value_2 in B. And the rows in B are specific to individual users with userid. What I need to do is make it also so that also checks if there are already N rows in B matching a A_id (either in value_1, or value_2) and userid, and if there are more than N rows, it doesn't select the A row.

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