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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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• 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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• SQLite3 and "cascade" SELECTion

  - by SK9

  I have a parent table and a child table related to the parent table by some REFERENCE. Suppose I exec a SELECT statement on the child and that it returns the at least one result. Can I arrange for my search to automatically yield all the content of all related parents with this child too? Or must I always take the reference from the child and put this in a second SELECT statement and exec this myself?

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• Question on different ways to link tables

  - by dotnetdev

  What is the difference between linking two tables and then the PK is an FK in the other table, but the FK has not got the primary key option (so it does not have the gold key), and having the PK in one table as a PK in another table? Am I right to think that the second option is for a many-to-many relationship? Thanks

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• Data from two tables without repeating data from the first?

  - by Aran

  I have two tables. Users table and Users Meta Table I am looking for a way to get all the information out of both tables with one query. But without repeating the information from Users table. This is all information relating to the users id number as well. So for example user_id = 1. Is there a way to query the database and collect all the information I from both tables without repeating the information from the first?

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• update record only works when there is no auto_increment

  - by every_answer_gets_a_point

  i am accessing a mysql table through an odbc connection in excel here is how i am updating the table: With rs .AddNew ' create a new record ' add values to each field in the record .Fields("datapath") = dpath .Fields("analysistime") = atime .Fields("reporttime") = rtime .Fields("lastcalib") = lcalib .Fields("analystname") = aname .Fields("reportname") = rname .Fields("batchstate") = "bstate" .Fields("instrument") = "NA" .Update ' stores the new record End With when the schema of the table is this, updating it works: create table batchinfo(datapath text,analysistime text,reporttime text,lastcalib text,analystname text, reportname text, batchstate text, instrument text); but when i have auto_increment in there it does not work: CREATE TABLE batchinfo ( rowid int(11) NOT NULL AUTO_INCREMENT, datapath text, analysistime text, reporttime text, lastcalib text, analystname text, reportname text, batchstate text, instrument text, PRIMARY KEY (rowid) ) ENGINE=InnoDB AUTO_INCREMENT=67 DEFAULT CHARSET=latin1 has anyone experienced a problem like this where updating does not work when there is an auto_increment field involved? connection string: Private Sub ConnectDB() Set oConn = New ADODB.Connection oConn.Open "DRIVER={MySQL ODBC 5.1 Driver};" & _ "SERVER=localhost;" & _ "DATABASE=employees;" & _ "USER=root;" & _ "PASSWORD=pas;" & _ "Option=3" End Sub also here's the rs.open: rs.Open "batchinfo", oConn, adOpenKeyset, adLockOptimistic, adCmdTable

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• How to convet DataTable to List on runtype with out existin class property [closed]

  - by shamim

  Work on VS2010 C#,Have one DataTable ,want to convert this DataTable to List Suppose: Table dt; On run time want to create similar field from a datatable and fill fields in List.There is no existing class for list properties. ListName=TableName List property name=Table column name List Property type=Table column type List items=Table rows Note: Recently work on EF.To fullfill my project requirement, need to give flexibility to use to input and execute ESQL at runtime .I don’t want to put this execute result on datatable or List ,want to put this result on list. List has no existing class and property,don’t want to convert DataTable on list Type:DataRow If have any query please ask,Thanks in advanced.

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• Fluent Nhibernate mapping related items

  - by Josh

  I am trying to relate 2 items. I have a table that is simply an Id field, and then 2 columns for the Item Id's to relate. I want it to be a 2 way relationship - that is, if the items appear twice in the table, I only want one relationship connection back. So, here's my item: public class Item { public virtual Guid ItemId {get; set;} public virtual string Name {get; set;} public virtual IList<Item> RelatedItems {get; set;} } The table for relating the items looks like this: CREATE TABLE RelatedItems ( RelatedItemId uniqueidentifier NOT NULL, ItemId uniqueidentifier NOT NULL, RelatedId uniqueidentifier NOT NULL, CONSTRAINT PK_RelatedItems PRIMARY KEY CLUSTERED (RelatedItemId) ) What is the best way to map this connection?

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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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• continuously fetch data from database using JAVA

  - by deathcaller

  Hi all, I've a scenario where my java program has to continuously communicate with the database table, example my java program has to get the data of my table when new rows are added to it at runtime. There should be continuous communication between my program and database. if the table has 10 rows initially and 2 rows are added by the user, it must detect this and return the rows. My program shouldn't use AJAX and timers. Please Help.

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• Customers and suppliers database design issue

  - by hectorsq

  I am developing a web application in which I will have customers and suppliers. Initially I thought on using a Customers table and a Suppliers table. Then when I was thinking on bank transactions, I noticed that each transaction needs to refer to a customer or a supplier, so I thought on using a single table named Business in which I will save both customers and suppliers. If I use Customers and Suppliers tables when I want to list the bank transactions I will have to search in both tables to get the company name. If I use a Businesses table I will have to use a business type column, and have the union of possible fields for all businesses types. Any suggestions on the design?

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• LAbeling with Percentage in R plot

  - by Libo Cannici

  Hi I have made this function that takes a table and prepare the label for a barplot prepare_labels <- function(ft){ labs <- ft labs <- paste(labs, "\n", sep="") labs <- paste(labs, round(prop.table(ft)*100,2), sep="") labs <- paste(labs, "%", sep="") return(labs) } It actually works fine, but is there any better way to write that function, the above code looks ugly and I want to write beautiful code :-) ex: ft <- table(mydata$phone_partner_products) prepare_labels(ft) [1] "3752\n34.09%" "226\n2.05%" "2907\n26.41%" "1404\n12.76%" "1653\n15.02%" [6] "1065\n9.68%"

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• The right way to write "ID" in columns in SQL

  - by radbyx

  My first question in here. I like the site so much :) I've a SQL table called Product. In that table I want to make a column for the ID of the product, and I really like to now the right way of write ID because I make alot of ID columns in the long run. So is it: "ID" or "Id" ? And also a foreign key in another table, is that called ProductID or ProductId? Thx guys.

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• TableView on Tab Bar Application ? Application is crashing.

  - by Andrei

  Steps to reproduce: 1. Create a Tab Bar Application called "TestApp" 2. Add new file, a UIViewController subclass with a XIB user interface called "Table" 3. Open up MainWindows.xib, click on the Second tab bar item and in Inspector change the NIB Name from "SecondView" to "Table". Save and close. 4. Open up Table.xib and drag a TableView on top of the view. Now link the dataSource and delegate outlets of the TableView to the Table.xib File's Owner. 5. Add the following code to Table.m: - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { NSLog(@"Returning num sections"); return 1; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { NSLog(@"Returning num rows"); return 1; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { NSLog(@"Trying to return cell"); static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease]; } cell.text = @"Hello"; NSLog(@"Returning cell"); return cell; } 6.Run the application and select the Second tab bar item. If I start with a View-based application, add a TableView to it, link the outlets to the File's owner and add that piece of code it all works just fine. What am I doing wrong ? Why is the application crashing ?

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• Debugging (displaying) SQL command sent to the db by SQLAlchemy

  - by morpheous

  I have an ORM class called Person, which wraps around a person table: After setting up the connection to the db etc, I run the ff statement. people = session.query(Person).all() The person table does not contain any data (as yet), so when I print the variable people, I get an empty list. I renamed the table referred to in my ORM class People, to people_foo (which does not exist). I then run the script again. I was surprised that no exception was thrown when attempting to access a table that does not exist. I therefore have the following 2 questions: How may I setup SQLAlchemy so that it propagates db errors back to the script? How may I view (i.e. print) the SQL that is being sent to the db engine If it helps, I am using PostgreSQL as the db

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• SQL Select -> product -> comments -> user

  - by user1492716

  thanks for yout time helping on this ;) I'm new to SQL and wish to solve somethign in just one query and i dont know how to do it.- Basically I've a table of products, a table of users and a table of comments, linked by products.id - comments.pid and user.id - comments.uid , i wish to know what is the best practice to create just 1 query and get all products with child comments, including username.

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• How would you write this Clojure snippet in Ruby and/or Haskell?

  - by dnolen

  I was working on a Rails template and was trying to write a bit of code that allows me to populate a table or multiple columns of ul tags "top-to-bottom" and "left-to-right" across however many columns I specify. I'm just getting the hang of Ruby so I couldn't figure this out. I'm also curious about an idiomatic Haskell version for this useful snippet. Improvements to Clojure version appreciated: (defn table [xs & {:keys [cols direction] :or {cols 1 direction 'right}}] (into [] (condp = direction 'down (let [c (count xs) q (int (/ c cols)) n (if (> (mod c q) 0) (inc q) q)] (apply map vector (partition n n (repeat nil) xs))) 'right (map vec (partition cols cols (repeat nil) xs))))) With this bit of code I can then do the following: (table (range 10) :cols 3) Printed out this would look like so: 0 1 2 3 4 5 6 7 8 9 And the trickier one: (table (range 10) :cols 3 :direction 'down) Looks like so: 0 4 8 1 5 9 2 6 3 7

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• Mysql with innodb and serializable transaction does not (always) lock rows

  - by Tobias G.

  Hello, I have a transaction with a SELECT and possible INSERT. For concurrency reasons, I added FOR UPDATE to the SELECT. To prevent phantom rows, I'm using the SERIALIZABLE transaction isolation level. This all works fine when there are any rows in the table, but not if the table is empty. When the table is empty, the SELECT FOR UPDATE does not do any (exclusive) locking and a concurrent thread/process can issue the same SELECT FOR UPDATE without being locked. CREATE TABLE t ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, display_order INT ) ENGINE = InnoDB; SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; START TRANSACTION; SELECT COALESCE(MAX(display_order), 0) + 1 from t FOR UPDATE; .. This concept works as expected with SQL Server, but not with MySQL. Any ideas on what I'm doing wrong? EDIT Adding an index on display_order does not change the behavior.

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• dynamic SQL not working as expected

  - by christine33990

  create or replace procedure createtables Authid current_user as begin execute immediate 'create table newcustomer as select * from customer'; end; create or replace procedure e is begin createtables; select * from newcustomer; end; I got two procedures above. first one will create a new tables called newcustomer, second procedure will call the first procedure and query to the newcustomer table. when I try to compile this code, it says the table is not yet created, I don't really get it as I have called createtables procedure so I assume I have created the table. Any help will be appreciated. Thanks

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• Multiple column foreign key contraints

  - by eugene4968

  I want to setup table constraints for the following scenario and I’m not sure how to do it or if it’s even possible in SQL Server 2005. I have three tables A,B,C. C is a child of B. B will have a optional foreign key(may be null) referencing A. For performance reasons I also want table C to have the same foreign key reference to table A. The constraint on table C should be that C must reference its parent (B) and also have the same foreign key reference to A as its parent. Anyone have any thoughts on how to do this?

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• In Lua, can I easily select the Nth result without custom functions?

  - by romkyns

  Suppose I am inserting a string into a table as follows: table.insert(tbl, mystring) and that mystring is generated by replacing all occurrences of "a" with "b" in input: mystring = string.gsub(input, "a", "b") The obvious way to combine the two into one statement doesn't work, because gsub returns two results: table.insert(tbl, string.gsub(input, "a", "b")) -- error! -- (second result of gsub is passed into table.insert) which, I suppose, is the price paid for supporting multiple return values. The question is, is there a standard, built-in way to select just the first return value? When I found select I thought that was exactly what it did, but alas, it actually selects all results from N onwards, and so doesn't help in this scenario. Now I know I can define my own select as follows: function select1(n, ...) return arg[n] end table.insert(tbl, select1(1, string.gsub(input, "a", "b"))) but this doesn't look right, since I'd expect a built-in way of doing this. So, am I missing some built-in construct? If not, do Lua developers tend to use a separate variable to extract the correct argument or write their own select1 functions?

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• How do i get an instance of the entity type based on MetaTable

  - by dimak

  is there a way to go from a MetaTable to an instance of an entity type so it can be queried with LINQ? What I want to do is this: MetaTable table = GridDataSource.GetTable (); var entity = table.GetInstanceOfEntity(); var test = (from t in entity select t).ToList(); where table.GetInstanceOfEntity() is something that I'm not sure how to implement. Thank you

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• Best index(es) to use for an OR Statement in SQL Server

  - by Chuck Haines

  I have a table which has a bunch of columns but the two relevant ones are: Due_Amount MONEY Bounced_Due_Amount MONEY I have a SQL query like the following SELECT * FROM table WHERE (Due_Amount 0 OR Bounced_Due_Amount 0) Would the best index to put on this table for SQL Server 2008 be an index which includes both columns in the index, or should I put an separate index on each column?

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• What is the difference between check and foreign key?

  - by GigaPr

  Hi, i am quite confused about the difference between a FOREIGN KEY and CHECK constraint. they appear to me to achieve the same result. I mean I could create a table and enforce a Foreign key on another table, but i could create a CHECK to ensure the value in in another table. What is the difference and when to use the one or the other? thanks

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• Adding a Image to UITable View Cell

  - by Graeme

  Hi, I have a table in which I want a dynamic image to load in at the left-hand side. The table needs to use an IF statement to select the appropriate image from the "Resources" folder, and needs to be based upon [dog types]. The [dog types] is extracted from an RSS feed, and so the image in the table cell needs to match the each cell's [dog types] tag. I suspect I need to use - (UIImage *)imageForTypes:(NSString *)types { to do such a thing. Thanks.

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