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• DB optimization to use it as a queue

  - by anony

  We have a table called worktable which has some columns(key(primary key), ptime, aname, status, content) we have something called producer which puts in rows in this table and we have consumer which does an order-by on the key column and fetches the first row which has status as 'pending'. The consumer does some processing on this row: 1. updates status to "processing" 2. does some processing using content 3. deletes the row we are facing contention issues when we try to run multiple consumers(probably due to the order-by which does a full table scan)... using Advanced queues would be our next step but before we go there we want to check what is the max throughput we can achieve with multiple consumers and producer on the table. What are the optimizations we can do to get the best numbers possible? Can we do an in-memory processing where a consumer fetches 1000 rows at a time processes and deletes? will that improve? What are other possibilities? partitioning of table? parallelization? Index organized tables?...

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• nhibernate activerecord lazy collection with custom query

  - by George Polevoy

  What i'm trying to accomplish, is having a temporal soft delete table. table Project(ID int) table ProjectActual(ProjectID int, IsActual bit, ActualAt datetime) Now is it possible to map a collection of actual projects, where project is actual when there is no record in ProjectActual.ProjectID = ID, or the last record sorted by ActualAt descending has IsActual set to 1 (true)?

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• running a stored procedure inside a sql trigger

  - by Ying

  Hi all, the business logic in my application requires me to insert a row in table X when a row is inserted in table Y. Furthermore, it should only do it between specific times(which I have to query another table for). I have considered running a script every 5 minutes or so to check this, but I stumbled upon triggers and figured this might be a better way to do it. But I find the syntax for procedures a little bewildering and I keep getting an error I have no idea how to fix. Here is where I start: CREATE TRIGGER reservation_auto_reply AFTER INSERT ON reservation FOR EACH ROW BEGIN IF NEW.sent_type = 1 /* In-App */ THEN INSERT INTO `messagehistory` (`trip`, `fk`, `sent_time`, `status`, `message_type`, `message`) VALUES (NEW.trip, NEW.psk, 'NOW()', 'submitted', 4, 'This is an automated reply to reservation'); END; I get an error in the VALUES part of the statmenet but im not sure where. I still have to query the other table for the information I need, but I can't even get past this part. Any help is appreciated, including links to many examples..Thanks

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• % confuses python raw sql query

  - by Jonathan

  Following this SO question, I'm trying to "truncate" all tables related to a certain django application using the following raw sql commands in python: cursor.execute("set foreign_key_checks = 0") cursor.execute("select concat('truncate table ',table_schema,'.',table_name,';') as sql_stmt from information_schema.tables where table_schema = 'my_db' and table_type = 'base table' AND table_name LIKE 'some_prefix%'") for sql in [sql[0] for sql in cursor.fetchall()]: cursor.execute(sql) cursor.execute("set foreign_key_checks = 1") Alas I receive the following error: C:\dev\my_project>my_script.py Traceback (most recent call last): File "C:\dev\my_project\my_script.py", line 295, in <module> cursor.execute(r"select concat('truncate table ',table_schema,'.',table_name,';') as sql_stmt from information_schema.tables where table_schema = 'my_db' and table_type = 'base table' AND table_name LIKE 'some_prefix%'") File "C:\Python26\lib\site-packages\django\db\backends\util.py", line 18, in execute sql = self.db.ops.last_executed_query(self.cursor, sql, params) File "C:\Python26\lib\site-packages\django\db\backends\__init__.py", line 216, in last_executed_query return smart_unicode(sql) % u_params TypeError: not enough arguments for format string Is the % in the LIKE making trouble? How can I workaround it?

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• UITableViewCell select even doesn't work

  - by saimun

  I had a page control(UIPageControl) on a view (UIViewController) with table view (UITableView) on each page, each page have own table and can go to different view controller. i add the codes in "didSelectRowAtIndexPath" which can go to next level, is works perfect when i test it in a table view by itself, but it doesn't works when i have page controller with it. - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { [tableView deselectRowAtIndexPath:indexPath animated:YES]; if (pageNumber == 0) { PicturesViewController *picturesView = [[PicturesViewController alloc] init]; [self.navigationController pushViewController:picturesView animated:YES]; [picturesView release]; } else if (pageNumber == 1) { PictureDetailViewController *pictureDetailView = [[PictureDetailViewController alloc] init]; [self.navigationController pushViewController:pictureDetailView animated:YES]; [pictureDetailView release]; } else if (pageNumber == 2) { MessagesViewController *messagesView = [[MessagesViewController alloc] init]; [self.navigationController pushViewController:messagesView animated:YES]; [messagesView release]; } } here is the code, if view directly to this table view this code is work, how can i make it work under the pagecontrol??

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• Creating a join based on data from other tables...

  - by Workshop Alex

  I'm dealing with a database structure that can be defined as "illogical". It has about 100 different schema's with all different table structures per schema. Only one common factor is a "Version" table in each schema containing about 4 fields. (Thus, there are about 100 Version tables in the database.) There's also another table (view, actually) containing a list of all the schema's in the database that have a version table. I need a stored procedure that walks through all the schema's and selects all data from the Version table, adding the schema name as a fifth field to the result. Basically, this stored procedure is to return a list of all version records per schema. My idea: first walk through the schema list to create one new SQL statements that will JOIN all the schema.version tables into one SQL statement. Then I return the result of that query. How to do this? Or does anyone have a better suggestion? (No, redesigning the structure is NOT an option.)

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• Distributing players to tables

  - by IVlad

  Consider N = 4k players, k tables and a number of clans such that each member can belong to one clan. A clan can contain at most k players. We want to organize 3 rounds of a game such that, for each table that seats exactly 4 players, no 2 players sitting there are part of the same clan, and, for the later rounds, no 2 players sitting there have sat at the same table before. All players play all rounds. How can we do this efficiently if N can be about ~80 large? I thought of this: for each table T: repeat until 4 players have been seated at T: pick a random player X that is not currently seated anywhere if X has not sat at the same table as anyone currently at T AND X is not from the same clan as anyone currently at T seat X at T break I am not sure if this will always finish or if it can get stuck even if there is a valid assignment. Even if this works, is there a better way to do it?

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• Fluent NHibernate - Set reference key columns to null

  - by Matt

  Hi, I have a table of Appointments and a table of AppointmentOutcomes. On my Appointments table I have an OutcomeID field which has a foreign key to AppointmentOutcomes. My Fluent NHibernate mappings look as follows; Table("Appointments"); Not.LazyLoad(); Id(c => c.ID).GeneratedBy.Assigned(); Map(c => c.Subject); Map(c => c.StartTime); References(c => c.Outcome, "OutcomeID"); Table("AppointmentOutcomes"); Not.LazyLoad(); Id(c => c.ID).GeneratedBy.Assigned(); Map(c => c.Description); Using NHibernate, if I delete an AppointmentOutcome an exception is thrown because the foreign key is invalid. What I would like to happen is that deleting an AppointmentOutcome would automatically set the OutcomeID of any Appointments that reference the AppointmentOutcome to NULL. Is this possible using Fluent NHibernate?

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• Mass data store with SQL SERVER

  - by Leo

  We need management 10,000 GPS devices, each GPS device upload a GPS data every 30 seconds, these data need to store in the database(MS SQL Server 2005). Each GPS device daily data quantity is: 24 * 60 * 2 = 2,880 10 000 10,000 GPS devices daily data quantity is: 10000 * 2880 = 28,800,000 Each GPS data approximately 160Byte, the amount of data per day is: 28,800,000 * 160 = 4.29GB We need hold at least 3 months of GPS data in the database, My question is: 1, whether SQL Server 2005 can support such a large amount of data store? 2, How to plan data table? (all GPS data storage in one table? Daily table? Each GPS device with a GPS data table?) The GPS data: GPSID varchar(21), RecvTime datetime, GPSTime datetime, IsValid bit, IsNavi bit, Lng float, Lat float, Alt float, Spd smallint, Head smallint, PulseValue bigint, Oil float, TSW1 bigint, TSW1Mask bigint, TSW2 bigint, TSW2Mask, BSW bigint, StateText varchar(200), PosText varchar(200), UploadType tinyint

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• Fetching a result twice with deferend name

  - by user1799842

  I have 1 table with tasks named opentask:columns: id,title,description,expires,creator_id,creator_name, executer_id, executer_name, priority_id, status_id1 table with users named user: with columns: user_id, username What I want is to create a query where there will be all columns from opentask table where the executer_id will be equal to the user_id of user table AND the creator_id will be equal to the user_id again. This creates a confusion because the first equality excludes the second.So I need somehow to create a query where I will include the usernames for the executer with something like where "opentask.executer_id=user_user_id" and at the same time I will include the username again (as a differend name?) for the creator with something like "where opentask.executer_id=user_user_id"So I try this, which of course I know that is missing something, can you help? SELECT DISTINCT id, title, description, expires, creator_id, executer_id, oc_opentask.priority_id, oc_opentask.status_id, priority_name, status_name, user_id, username, (SELECT username FROM oc_opentask, oc_user WHERE oc_opentask.creator_id=oc_user.user_id) AS username2 FROM oc_opentask, oc_opentask_priority, oc_user, oc_opentask_status WHERE oc_opentask.priority_id=oc_opentask_priority.priority_id AND oc_opentask.executer_id=oc_user.user_id AND oc_opentask.status_id=oc_opentask_status.status_id ORDER BY oc_opentask.expires DESC

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• Logic: Best way to sample & count bytes of a 100MB+ file

  - by Jami

  Let's say I have this 170mb file (roughly 180 million bytes). What I need to do is to create a table that lists: all 4096 byte combinations found [column 'bytes'], and the number of times each byte combination appeared in it [column 'occurrences'] Assume two things: I can save data very fast, but I can update my saved data very slow. How should I sample the file and save the needed information? Here're some suggestions that are (extremely) slow: Go through each 4096 byte combinations in the file, save each data, but search the table first for existing combinations and update it's values. this is unbelievably slow Go through each 4096 byte combinations in the file, save until 1 million rows of data in a temporary table. Go through that table and fix the entries (combine repeating byte combinations), then copy to the big table. Repeat going through another 1 million rows of data and repeat the process. this is faster by a bit, but still unbelievably slow This is kind of like taking the statistics of the file. NOTE: I know that sampling the file can generate tons of data (around 22Gb from experience), and I know that any solution posted would take a bit of time to finish. I need the most efficient saving process

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• Is it possible to cache all the data in a SQL Server CE database using LinqToSql?

  - by DanM

  I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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• How to display mysql records as preselected checkboxes?

  - by Jennifer

  I have a table column called post_tags within a table called posts where assigned tags are stored separated by the @ symbol. I also have a table called tags where all tag names are stored. I would like to design my database in a more normalized way but for the purpose I am trying to achieve this is the easiest option. Anyway, I want to display on the screen all the entries from the tags table as checkboxes, so I do: $query = mysql_query("SELECT * FROM tags ORDER BY name"); while ($row = mysql_fetch_assoc($query)) { $tag = $row['name']; echo "<input type='checkbox' name='tags[]' value='$tag' />\n"; } Next I want to have the tags that are assigned to a particular post be preselected. For example, if I have a post with the following in it's post_tags column: party@beaches@dolphins@ I want the "party", "beaches" and "dolphin" checkboxes to be checked by default (while the checkboxes for the other options are unchecked). How can this be done?

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• NSTableView doesn't populate with array objects until a new object is added via the controller

  - by Luke

  I have an NSTableView and an array controller set up as shown here, using cocoa bindings: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/TableView/PopulatingViewTablesWithBindings/PopulatingView-TablesWithBindings.html#//apple_ref/doc/uid/10000026i-CH13-SW3 In my app delegate during applicationDidFinishLaunching I have the following snippet in here, initialising the array and filling it with objects array = [[NSMutableArray alloc] init]; SomeObject* foo = [[Object alloc] init]; foo.text = @"sup"; [array addObject:foo]; //Repeat this a few times However, when I build the app and run it I end up with an empty table. However, if I bind a button to the array controller's add: input and click it during runtime (this adds a new object to the array and table) then the table will show the new object first, with the objects added during applicationDidFinishLaunching following it. Why does this happen? And is there a way to make my table populate without having to add an element first?

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• [SQL] Getting the sum of several columns from two tables

  - by romaintaz

  I want to get the sum of several columns from 2 different tables (these tables share the same structure). If I only consider one table, I would write this kind of query: SELECT MONTH_REF, SUM(amount1), SUM(amount2) FROM T_FOO WHERE seller = XXX GROUP BY MONTH_REF; However, I would like to also work with the data from the table T_BAR, and then have a select query that return the following columns: MONTH_REF SUM(T_FOO.amount1) + SUM(T_BAR.amount1) SUM(T_FOO.amount2) + SUM(T_BAR.amount2) everything grouped by the value of MONTH_REF. Note that a record for a given MONTH_REF can be found in one table but not in the other table. In this case, I would like to get the sum of T_FOO.amount1 + 0 (or 0 + T_BAR.amount1). How can I write my SQL query to get this information? For information, my database is Oracle 10g.

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• MySQLi String comparisons using keys

  - by asdasd

  I have a table with lets say 2 columns. id number, and value. Value is a string (var char). Lets say i have a number x, and a list of numbers a1, a2, a3, a4, a5..... where x is not in the list. All of these numbers correspond to a unique row in the table. I want to know if the string value for x in the table is contained in one of the string values for any table entry for a1, a2, a3, a4... Lets say i have these rows: x, aaa a1, bbb a2, ccc a3, ddd a4, aaabbbcc then i want somehow a confirmation that yes, the value for x is included in one of the values in my list of numbers (a4 contains x). I know i can do this in a couple queries and shove it down some PHP and get my answer. But can i do this with one query?

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• 'cross-referencing' DataTable's

  - by Lee

  I have a DataGridView that is being filled with data from a table. Inside this table is a column called 'group' that has the ID of an individual group in another table. What I would like to do, is when the DataGridView is filled, instead of showing the ID contained in 'group', I'd like it to display the name of the group. Is there some type of VB.net 'magic' that can do this, or do I need to cross-reference the data myself? Here is a breakdown of what the 2 tables look like: table1 id group (this holds the value of column id in table 2) weight last_update table2 id description (this is what I would like to be displayed in the DGV.) BTW - I am using Visual Studio Express.

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• How to write query for remove and alter unique columns

  - by Shiny

  My scenario..Im using SqlCompactServer Edition .I'm creating table Create Table SSr( name nvarchar(400),id int unique).I need to alter table and make name as UNIQUE Column and remove unique from existing column. How to Achieve this.

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• Looking for nice Javascript/jQuery code for displaying large tables

  - by misha-moroshko

  I have an HTML table which may contain thousands of rows (number of columns is not a problem here). I would like to be able to browse this table easily and be able to do the following: Decide how many rows will be presented Jump to the next/previous X number of rows Scroll the table using the scroll bars to any desired line Be able to customize/extend easily this Javascript/jQuery code Has anyone seen something similar ? Thank you very much !

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• Mysql - wondering about scaling a twitter-like application ?

  - by user246114

  Hi, I'm developing an app that is vaguely similar to twitter, in that it allows users to follow one another. I wanted to do this using google app engine, for its scalability promises, but it's proving kind of difficult to get running for a few different reasons. I'd basically like to have a _users table, and a _followers table. Users go into the users table, follower relationships go into _followers. The problem is that each row in the users table will probably have like 100 corresponding records in the _followers table as users start following one another. So the number of rows is going to explode quickly. Using app engine, the volume [shouldn't] be a problem. If I go with mysql, and I do actually start to get some traction, how do I scale this up? Am I going to just end up moving to a distributed database in the end anyway? Should I fight it out with google app engine? I read that Twitter was using mysql, and they've run into this problem, and are now switching to cassandra. Thanks

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• Multiple ID's in database

  - by eric

  I have a database that contains a few tables such as person, staff, member, and supporter. The person table contains information about every staff, member, and supporter. The information it contains is name,address,email, and telephone. I also created an id that is the primary key. My issue is that I also have an primary key ID for staff, member, and supporter. For instance, in the person table is John with id 1. He is a supporter so in the supporter table is pID(for person id)to reference back to John with all his information and ID(for supporter ID). pID references to the person table and every person has an ID incremented by 1 starting at 1. supporter ID is for every supporter and also starts at 1 and is incremented by 1. Is it possible to have in the supporter table pID = 1 and supporter ID = 1? Another person may have a pID = 26 and supporter ID = 5. Or will supporter ID have to be different than the pID and be something like "sup"? So you would have pID = 1 and supporter ID = sup1 or pID = 26 and supporter ID = sup5

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• SQL: find entries in 1:n relation that don't comply with condition spanning multiple rows

  - by milianw

  I'm trying to optimize SQL queries in Akonadi and came across the following problem that is apparently not easy to solve with SQL, at least for me: Assume the following table structure (should work in SQLite, PostgreSQL, MySQL): CREATE TABLE a ( a_id INT PRIMARY KEY ); INSERT INTO a (a_id) VALUES (1), (2), (3), (4); CREATE TABLE b ( b_id INT PRIMARY KEY, a_id INT, name VARCHAR(255) NOT NULL ); INSERT INTO b (b_id, a_id, name) VALUES (1, 1, 'foo'), (2, 1, 'bar'), (3, 1, 'asdf'), (4, 2, 'foo'), (5, 2, 'bar'), (6, 3, 'foo'); Now my problem is to find entries in a that are missing name entries in table b. E.g. I need to make sure each entry in a has at least the name entries "foo" and "bar" in table b. Hence the query should return something similar to: a_id = 3 is missing name "bar" a_id = 4 is missing name "foo" and "bar" Since both tables are potentially huge in Akonadi, performance is of utmost importance. One solution in MySQL would be: SELECT a.a_id, CONCAT('|', GROUP_CONCAT(name ORDER BY NAME ASC SEPARATOR '|'), '|') as names FROM a LEFT JOIN b USING( a_id ) GROUP BY a.a_id HAVING names IS NULL OR names NOT LIKE '%|bar|foo|%'; I have yet to measure the performance tomorrow, but severly doubt it's any fast for tens of thousand of entries in a and thrice as many in b. Furthermore we want to support SQLite and PostgreSQL where to my knowledge the GROUP_CONCAT function is not available. Thanks, good night.

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• UITableView animations for a "lazy" UI design?

  - by donuts

  I have a UITableViewController that allows the user to perform editing tasks. Now, once a user has committed his change, the table view doesn't directly change the model and updates the table, rather "informs" the model what the user wants to do. The model in turn updates accordingly and then posts a notification that it has been changed. As far as I've seen, I need to begin/end updates on the tableview and in between change the model to its' final form. My changes though, are asynchronous and cannot guarantee to update the model before 'tableview endupdates' is called. Currently, each time I receive a 'model did change' notificaiton, I reload the entire table. So, how can I really make cell animations (delete/insert) work? Should the model fire a notification for each little change instead of the entire table?

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• How to save to two tables using one SQLAlchemy model

  - by Oatman

  I have an SQLAlchemy ORM class, linked to MySQL, which works great at saving the data I need down to the underlying table. However, I would like to also save the identical data to a second archive table. Here's some psudocode to try and explain what I mean my_data = Data() #An ORM Class my_data.name = "foo" #This saves just to the 'data' table session.add(my_data) #This will save it to the identical 'backup_data' table my_data_archive = my_data my_data_archive.__tablename__ = 'backup_data' session.add(my_data_archive) #And commits them both session.commit() Just a heads up, I am not interested in mapping a class to a JOIN, as in: http://www.sqlalchemy.org/docs/05/mappers.html#mapping-a-class-against-multiple-tables

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• How to import csv files

  - by Manoj Wadhwani

  How can I import CSV file data into SQL Server 2000 table? I need to insert data from CSV file to table twice a day. Table has more then 20 fields but I only need to insert value into 6 fields.

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