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• Check For Duplicate Records VS try/catch Unique Key Constraint

  - by Jed

  I have a database table that has a Unique Key constraint defined to avoid duplicate records from occurring. I'm curious if it is bad practice to NOT manually check for duplicate records prior to running an INSERT statement on the table. In other words, should I run a SELECT statement using a WHERE clause that checks for duplicate values of the record that I am about to INSERT. If a record is found, then do not run the INSERT statement, otherwise go ahead and run the INSERT.... OR Just run the INSERT statement and try/catch the exception that may be thrown due to a Unique Key violation. I'm weighing the two perspectives and can't decide which is best- 1. Don't waste a SELECT call to check for duplicates when I can just trap for an exception VS 2. Don't be lazy by implementing ugly try/catch logic VS 3. ???Your thoughts here??? :)

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• Help with hash tables and quadratic probing in Java

  - by user313458

  I really need help with inserting into a hash table. I'm just not totally getting it right now. Could someone explain quadratic and linear probing in layman's terms? public void insert(String key) { int homeLocation = 0; int location = 0; int count = 0; if (find(key).getLocation() == -1) // make sure key is not already in the table { //****** ADD YOUR CODE HERE FOR QUADRATIC PROBING ******** } } This is the code I'm working on. I'm not asking anyone to do it, I just really need help with learning the whole concept Any help would be greatly appreciated.

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• SQL Alchemy related Objects Error

  - by alex

  from sqlalchemy.orm import relation, backref from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey, Date, Sequence from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class GUI_SCENARIO(Base): __tablename__ = 'GUI_SCENARIO' Scenario_ID = Column(Integer, primary_key=True) Definition_Date = Column(Date) guiScenarioDefinition = relation('GUI_SCENARIO_DEFINITION', order_by='GUI_SCENARIO_DEFINITION.Scenario_Definition_ID', backref='guiScenario') def __init__(self, Scenario_ID=None, Definition_Date=None): self.Scenario_ID = Scenario_ID self.Definition_Date = Definition_Date class GUI_SCENARIO_DEFINITION(Base): __tablename__='GUI_SCENARIO_DEFINITION' Scenario_Definition_ID = Column(Integer, Sequence('Scenario_Definition_ID_SEQ'), primary_key=True) Scenario_FK = Column(Integer, ForeignKey('GUI_SCENARIO.Scenario_ID')) Definition_Date=Column(Date) guiScenario = relation(GUI_SCENARIO, backref=backref('guiScenarioDefinition', order_by=Scenario_Definition_ID)) def __init__(self, Scenario_FK, Definition_Date): self.Scenario_FK = Scenario_FK self.Definition_Date = Definition_Date guiScenario = relation(GUI_SCENARIO, backref=backref('guiScenarioDefinition', order_by=Scenario_Definition_ID)) tableNameScenario = "GUI_SCENARIO" scenarioClass = getattr(MappingTablesScenario, tableNameScenario) tableScenario = Table(tableNameScenario, meta, autoload=True) mapper(scenarioClass, tableScenario) scenarioName = scenarioDefinition.name scenarioDefinitionDate = datetime.today() newScenario = MappingTablesScenario.GUI_SCENARIO(scenarioName, scenarioDefinitionDate) print newScenario.guiScenarioDefinition If I try to get the objects related to a scenarioObject, I always get this error: AttributeError: 'GUI_SCENARIO' object has no attribute 'guiScenarioDefinition' Does anyone know, why I get this error?

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• Finding gaps (missing records) in database records using SQL

  - by Tony_Henrich

  I have a table with records for every consecutive hour. Each hour has some value. I want a T-SQL query to retrieve the missing records (missing hours, the gaps). So for the DDL below, I should get a record for missing hour 04/01/2010 02:00 AM (assuming date range is between the first and last record). Using SQL Server 2005. Prefer a set based query. DDL: CREATE TABLE [Readings]( [StartDate] [datetime] NOT NULL, [SomeValue] [int] NOT NULL ) INSERT INTO [Readings]([StartDate], [SomeValue]) SELECT '20100401 00:00:00.000', 2 UNION ALL SELECT '20100401 01:00:00.000', 3 UNION ALL SELECT '20100401 03:00:00.000', 45

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• Why is my iPhone SDK 3.2 iPad code showing a white screen?

  - by Anthony Glyadchenko

  I'm trying to get a UISplitViewController working with an iPad app. I have the table view controller linked up under the Master pane and a plain UIView under the Detail view. I also have [window addSubview:splitView.view]; in my code. For some reason I just get a white screen even though the table view controller code is properly coded and linked under my nib. Any help would be great! Thanks! Here's where you can find the code: http://drop.io/s28bu4t/asset/mydevice-hd-zip

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• Enforcing a query in MySql to use a specific index

  - by Hossein

  Hi, I have large table. consisting of only 3 columns (id(INT),bookmarkID(INT),tagID(INT)).I have two BTREE indexes one for each bookmarkID and tagID columns.This table has about 21 Million records. I am trying to run this query: SELECT bookmarkID,COUNT(bookmarkID) AS count FROM bookmark_tag_map GROUP BY tagID,bookmarkID HAVING tagID IN (-----"tagIDList"-----) AND count >= N which takes ages to return the results.I read somewhere that if make an index in which it has tagID,bookmarkID together, i will get a much faster result. I created the index after some time. Tried the query again, but it seems that this query is not using the new index that I have made.I ran EXPLAIN and saw that it is actually true. My question now is that how I can enforce a query to use a specific index? also comments on other ways to make the query faster are welcome. Thanks

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• Using CSS, how can I make overflow:visible; contents overlap adjacent <td> cells?

  - by Structure

  I have the following CSS style code for my table: td { overflow: hidden; white-space:nowrap; } td:hover { overflow: visible; } However, when I hover over a <td> element whos contents (text) are hidden, the result is that the contents become visible but are behind the content of the adjacent cell (right side). I do not think that z-index can be applied to table cell elements, so is there a CSS attribute that I can specify within my td:hover style which will make the content of my <td> tag overlap the content in adjacent cells?

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• How can I edit a css rule in jQuery?

  - by chacham15

  The purpose is that rows are dynamically added to a table and it is not as nice (and slower) to apply the rule manually later. The specific example is that I am creating a tree table to represent a folder directory. Each folder is a div. In each div, there is a ul with an li for each columns' information. These li have a class name equivalent to the column name. This provides column width. I want to make the columns resizable however. I could do $('.className').css('width', newWidth) but then this wont apply to newly inserted items. Therefore, I want to modify the css rule. How do I do this?

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• Putting update logic in your migrations

  - by Daniel Abrahamsson

  A couple of times I've been in the situation where I've wanted to refactor the design of some model and have ended up putting update logic in migrations. However, as far as I've understood, this is not good practice (especially since you are encouraged to use your schema file for deployment, and not your migrations). How do you deal with these kind of problems? To clearify what I mean, say I have a User model. Since I thought there would only be two kinds of users, namely a "normal" user and an administrator, I chose to use a simple boolean field telling whether the user was an adminstrator or not. However, after I while I figured I needed some third kind of user, perhaps a moderator or something similar. In this case I add a UserType model (and the corresponding migration), and a second migration for removing the "admin" flag from the user table. And here comes the problem. In the "add_user_type_to_users" migration I have to map the admin flag value to a user type. Additionally, in order to do this, the user types have to exist, meaning I can not use the seeds file, but rather create the user types in the migration (also considered bad practice). Here comes some fictional code representing the situation: class CreateUserTypes < ActiveRecord::Migration def self.up create_table :user_types do |t| t.string :name, :nil => false, :unique => true end #Create basic types (can not put in seed, because of future migration dependency) UserType.create!(:name => "BASIC") UserType.create!(:name => "MODERATOR") UserType.create!(:name => "ADMINISTRATOR") end def self.down drop_table :user_types end end class AddTypeIdToUsers < ActiveRecord::Migration def self.up add_column :users, :type_id, :integer #Determine type via the admin flag basic = UserType.find_by_name("BASIC") admin = UserType.find_by_name("ADMINISTRATOR") User.all.each {|u| u.update_attribute(:type_id, (u.admin?) ? admin.id : basic.id)} #Remove the admin flag remove_column :users, :admin #Add foreign key execute "alter table users add constraint fk_user_type_id foreign key (type_id) references user_types (id)" end def self.down #Re-add the admin flag add_column :users, :admin, :boolean, :default => false #Reset the admin flag (this is the problematic update code) admin = UserType.find_by_name("ADMINISTRATOR") execute "update users set admin=true where type_id=#{admin.id}" #Remove foreign key constraint execute "alter table users drop foreign key fk_user_type_id" #Drop the type_id column remove_column :users, :type_id end end As you can see there are two problematic parts. First the row creation part in the first model, which is necessary if I would like to run all migrations in a row, then the "update" part in the second migration that maps the "admin" column to the "type_id" column. Any advice?

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• Function returns CSV File: How to go about checking it ?

  - by Rachel

  I am doing something like: $outputFile = getCurrentDBSnapshot($data); where $data is the resource stream that am passing in, basically from command prompt am passing an file and am opening it using fopen for writing with 'w+' permissions, now getCurrentDBSnapshot would get the current state of a table and would update the $data csv file, so basically $outputFile would be updated with the current state of database table, now I want to var_dump or print the value of $outputFile to see the data present into it. But when I do $this->fout = fopen($outputFile,'r') or die('Cannot open file'); $test = fgetcsv($outputFile,5000,":"); var_dump($test); It gives me an error saying that it expects parameter 1 to be a string type and am passing resource. My goal to see the contains of $outputFile and so my question is that How can I see the contains present in $outputFile or how can I see what getcurrentDBSnapshot function is returning me ?

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• ASP.NET membership spaces in username

  - by SaphuA

  Hi, We just came across a weird bug in our application that uses the asp.net membership. The administrator had created some users with spaces behind their name: 'My Username ' In the Users table this is saved normally, so without the spaces: 'My Username' The user can also login using the name without the spaces: 'My Username' When we use User.Identity.Name in our applicatie the result is the username WITH the spaces: 'My Username '. Where do these spaces come from? They aren't stored in the Users table so where does he get this from?! Thanks!

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• How to merge two tables based on common column and sort the results by date

  - by techiepark

  Hello friends, I have two mysql tables and i want to merge the results of these two tables based on the common column rev_id. The merged results should be sorted by the date of two tables. Please help me. CREATE TABLE `reply` ( `id` int(3) NOT NULL auto_increment, `name` varchar(25) NOT NULL default '', `member_id` varchar(45) NOT NULL, `rev_id` int(3) NOT NULL default '0', `description` text, `post_date` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP, `flag` char(2) NOT NULL default 'N', PRIMARY KEY (`id`), KEY `member_id` (`member_id`) ) ENGINE=MyISAM; CREATE TABLE `comment` ( `com_id` int(8) NOT NULL auto_increment, `rev_id` int(5) NOT NULL default '0', `member_id` varchar(50) NOT NULL, `comm_desc` text NOT NULL, `date_created` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP, PRIMARY KEY (`com_id`), KEY `member_id` (`member_id`) ) ENGINE=MyISAM;

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• Converting "is null" into a linq to sql statement

  - by Darryl Braaten

  I am having trouble replicating the following sql as a LINQ statement select TableA.* from TableA left outer join TableAinTableB on TableA.Id = TableAId where TableBId is null The following returns no lines from TableA in db.TableA join AinB in db.TableAinTableB on TableA.Id equals TableAId where AinB.TableBId == null select TableA Also tried and a few other things that didn't work. from TableA in db.TableA join AinB in db.TableAinTableB on TableA.Id equals TableAId where AinB == null select TableA TableAinTableB is a many to many table. The query I want will pull all the records from TableA that have no records in the middle table. My sql does what I want but I have no idea how to convert it to LINQ to SQL. I ended up working around it by just doing a db.ExecuteQuery("working sql"); But I would like to know if the query is possible in LINQ and how to write it, or a pointer to a document that covers this scenario. My searching did not uncover anything I found useful.

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• DataBinding a DropDownList in ASP.NET MVC 2

  - by Daniel Coffman

  I'm extremely frustrated trying to switch to MVC after a couple years of webforms development. Here's my extremely simple problem that I can't manage to solve: I have a list of States in a table called StateProvince. I have a DropDownList. I want the DropDownList to display all of the States in the StateProvince table and post the selected state back on HTTP PUT. This is what I'm doing: <%: Html.DropDownListFor(model = model.StateProvinceId, new SelectList(Model.StateProvinces, "StateProvinceId", "Name") )% I'm getting an Object reference not set to an instance of an object. Why? How can I make this work? Keep it simple, I know nothing about MVC.

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• Why index_merge is not used here?

  - by user198729

  Setup: mysql> create table t(a integer unsigned,b integer unsigned); mysql> insert into t(a,b) values (1,2),(1,3),(2,4); mysql> create index i_t_a on t(a); mysql> create index i_t_b on t(b); mysql> explain select * from t where a=1 or b=4; +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | t | ALL | i_t_a,i_t_b | NULL | NULL | NULL | 3 | Using where | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ Is there something I'm missing?

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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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• MySQL Select problems

  - by John Nuñez

  Table #1: qa_returns_items Table #2: qa_returns_residues I have a long time trying to get this Result: item_code - item_quantity 2 - 1 3 - 2 IF qa_returns_items.item_code = qa_returns_residues.item_code AND status_code = 11 THEN item_quantity = qa_returns_items.item_quantity - qa_returns_residues.item_quantity ELSEIF qa_returns_items.item_code = qa_returns_residues.item_code AND status_code = 12 THEN item_quantity = qa_returns_items.item_quantity + qa_returns_residues.item_quantity ELSE show diferendes END IF I tried this Query: select SubQueryAlias.item_code, total_ecuation, SubQueryAlias.item_unitprice, SubQueryAlias.item_unitprice * total_ecuation as item_subtotal, item_discount, (SubQueryAlias.item_unitprice * total_ecuation) - item_discount as item_total from ( select ri.item_code , case status_code when 11 then ri.item_quantity - rr.item_quantity when 12 then ri.item_quantity + rr.item_quantity end as total_ecuation , rr.item_unitprice , rr.item_quantity , rr.item_discount * rr.item_quantity as item_discount from qa_returns_residues rr left join qa_returns_items ri on ri.item_code = rr.item_code WHERE ri.returnlog_code = 1 ) as SubQueryAlias where total_ecuation > 0 GROUP BY (item_code); The query returns this result: item_code - item_quantity 1 - 2 2 - 2

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• Reading correctly alphanumeric fields into R

  - by gd047

  A tab-delimited text file, which is actually an export (using bcp) of a database table, is of that form: 102 1 01 e113c 3224.96 12 102 1 01 e185 101127.25 12 102 2 01 e185 176417.90 12 102A 3 01 e185 26261.03 12 I tried to import it in R with a command like data <- read.delim("C:\\test.txt", header = FALSE, sep = "\t") The problem is that the 3rd column which is actually a varchar field (alphanumeric) is mistakenly read as integer (as there are no letters in the entire column) and the leading zeros disappeared. The same thing happened when I imported the data directly from the database, using odbcConnect. Again that column was read as integer. str(data) $ code: int 1 1 1 1 1 1 6 1 1 8 ... How can I import such a dataset in R correctly, so as to be able to safely populate that db table again, after doing some data manipulations?

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• Help need to with MySQL query to join data spanning multiple tables and use data as column names

  - by gurun8

  I need a little help putting together a SQL query that will give me the following resultsets: and The data model looks like this: The tricky part for me is that the columns to the right of the "Product" in the resultset aren't really columns in the database but rather key/value pairs spanned across the data model. Table data is as follows: My apologies in advance for the image heavy question and the image quality. This just seemed like the easiest way to convey the information. It'll probably take someone less time to write the query statement to achieve the results than it did for me to assemble this question. By the way, the "product_option" table image is truncated but it illustrated the general idea of the data structure. The MySQL server version is 5.1.45.

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• Stop duplicate icmp echo replies when bridging to a dummy interface?

  - by mbrownnyc

  I recently configured a bridge br0 with members as eth0 (real if) and dummy0 (dummy.ko if). When I ping this machine, I receive duplicate replies as: # ping SERVERA PING SERVERA.domain.local (192.168.100.115) 56(84) bytes of data. 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=114 ms (DUP!) 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms (DUP!) Using tcpdump on SERVERA, I was able to see icmp echo replies being sent from eth0 and br0 itself as follows (oddly two echo request packets arrive "from" my Windows box myhost): 23:19:05.324192 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324212 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324217 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324221 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324264 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324272 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 It's worth noting, testing reveals that hosts on the same physical switch do not see DUP icmp echo responses (a host on the same VLAN on another switch does see a dup icmp echo response). I've read that this could be due to the ARP table of a switch, but I can't find any info directly related to bridges, just bonds. I have a feeling my problem lay in the stack on linux, not the switch, but am opened to any suggestions. The system is running centos6/el6 kernel 2.6.32-71.29.1.el6.i686. How do I stop ICMP echo replies from being sent in duplicate when dealing with a bridge interface/bridged interfaces? Thanks, Matt [edit] Quick note: It was recommended in #linux to: [08:53] == mbrownnyc [gateway/web/freenode/] has joined ##linux [08:57] <lkeijser> mbrownnyc: what happens if you set arp_ignore to 1 for the dummy interface? [08:59] <lkeijser> also set arp_announce to 2 for that interface [09:24] <mbrownnyc> lkeijser: I set arp_annouce to 2, arp_ignore to 2 in /etc/sysctl.conf and rebooted the machine... verifying that the bits are set after boot... the problem is still present I did this and came up empty. Same dup problem. I will be moving away from including the dummy interface in the bridge as: [09:31] == mbrownnyc [gateway/web/freenode/] has joined #Netfilter [09:31] <mbrownnyc> Hello all... I'm wondering, is it correct that even with an interface in PROMISC that the kernel will drop /some/ packets before they reach applications? [09:31] <whaffle> What would you make think so? [09:32] <mbrownnyc> I ask because I am receiving ICMP echo replies after configuring a bridge with a dummy interface in order for ipt_netflow to see all packets, only as reported in it's documentation: http://ipt-netflow.git.sourceforge.net/git/gitweb.cgi?p=ipt-netflow/ipt-netflow;a=blob;f=README.promisc [09:32] <mbrownnyc> but I do not know if PROMISC will do the same job [09:33] <mbrownnyc> I was referred here from #linux. any assistance is appreciated [09:33] <whaffle> The following conditions need to be met: PROMISC is enabled (bridges and applications like tcpdump will do this automatically, otherwise they won't function). [09:34] <whaffle> If an interface is part of a bridge, then all packets that enter the bridge should already be visible in the raw table. [09:35] <mbrownnyc> thanks whaffle PROMISC must be set manually for ipt_netflow to function, but [09:36] <whaffle> promisc does not need to be set manually, because the bridge will do it for you. [09:36] <whaffle> When you do not have a bridge, you can easily create one, thereby rendering any kernel patches moot. [09:36] <mbrownnyc> whaffle: I speak without the bridge [09:36] <whaffle> It is perfectly valid to have a "half-bridge" with only a single interface in it. [09:36] <mbrownnyc> whaffle: I am unfamiliar with the raw table, does this mean that PROMISC allows the raw table to be populated with packets the same as if the interface was part of a bridge? [09:37] <whaffle> Promisc mode will cause packets with {a dst MAC address that does not equal the interface's MAC address} to be delivered from the NIC into the kernel nevertheless. [09:37] <mbrownnyc> whaffle: I suppose I mean to clearly ask: what benefit would creating a bridge have over setting an interface PROMISC? [09:38] <mbrownnyc> whaffle: from your last answer I feel that the answer to my question is "none," is this correct? [09:39] <whaffle> Furthermore, the linux kernel itself has a check for {packets with a non-local MAC address}, so that packets that will not enter a bridge will be discarded as well, even in the face of PROMISC. [09:46] <mbrownnyc> whaffle: so, this last bit of information is quite clearly why I would need and want a bridge in my situation [09:46] <mbrownnyc> okay, the ICMP echo reply duplicate issue is likely out of the realm of this channel, but I sincerely appreciate the info on the kernels inner-workings [09:52] <whaffle> mbrownnyc: either the kernel patch, or a bridge with an interface. Since the latter is quicker, yes [09:54] <mbrownnyc> thanks whaffle [edit2] After removing the bridge, and removing the dummy kernel module, I only had a single interface chilling out, lonely. I still received duplicate icmp echo replies... in fact I received a random amount: http://pastebin.com/2LNs0GM8 The same thing doesn't happen on a few other hosts on the same switch, so it has to do with the linux box itself. I'll likely end up rebuilding it next week. Then... you know... this same thing will occur again. [edit3] Guess what? I rebuilt the box, and I'm still receiving duplicate ICMP echo replies. Must be the network infrastructure, although the ARP tables do not contain multiple entries. [edit4] How ridiculous. The machine was a network probe, so I was (ingress and egress) mirroring an uplink port to a node that was the NIC. So, the flow (must have) gone like this: ICMP echo request comes in through the mirrored uplink port. (the real) ICMP echo request is received by the NIC (the mirrored) ICMP echo request is received by the NIC ICMP echo reply is sent for both. I'm ashamed of myself, but now I know. It was suggested on #networking to either isolate the mirrored traffic to an interface that does not have IP enabled, or tag the mirrored packets with dot1q.

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• Two separate fields need to be grouped in one group

  - by Sigita

  I have two fields: Mother's employer and Father's employer, and I need to group on the employer. Could somebody help me combine the two above fields into one group? Both fields are in one table. FOr example a child named John Lewis is a record in a table and he has a father and a mother and Mother's employer is IBM and Father's employer is ISF. And so forth. I need to come up with a list By employer where it would show: Employer: IBM John Lewis Emplyer: ISF John Lewis Employer: .... Thank you, Sigita

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• How can i query for null values in entity framework?

  - by AZ

  I want to execute a query like this var result = from entry in table where entry.something == null select entry; and get an IS NULL generated. Edited: After the first two answers i feel the need to clarify that I'm using Entity Framework and not Linq to SQL. The object.Equals() method does not seem to work in EF. Edit no.2: The above query works as intended. It correctly generates IS NULL. My production code however was var value = null; var result = from entry in table where entry.something == value select entry; and the generated SQL was something = @p; @p = NULL. It seems that EF correctly translates the constant expression but if a variable is involved it treats it just like a normal comparison. Makes sense actually. I'll close this question

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• How to define one-to-many connection between a same model through another model

  - by Mekajiki

  I want to define one-to-many relationship as follows; User has one introducer User has many newcomers(who is introduced by the user) Use "Introduction" model instead of adding a column to users table. My table and model definition is as follows; DB Scheme: create_table "introductions", force: true do |t| t.integer "introducer_id" t.integer "newcomer_id" t.datetime "created_at" t.datetime "updated_at" User model: class User < ActiveRecord::Base has_many :introductions, foreign_key: :introducer_id has_many :newcomers, through: :introductions, source: :newcomer belongs_to :introduction, foreign_key: :newcomer_id belongs_to :introducer end Introduction model: class Introduction < ActiveRecord::Base belongs_to :introducer, class_name: 'User' belongs_to :newcomer, class_name: 'User' end This works fine: user1.newcomers.push user2 but, user2.introducer # => nil How can I define belongs_to relationship correctly?

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• MySQL top count({column}) with a limit

  - by Josh K

  I have a table with an ip address column. I would like to find the top five addresses which are listed. Right now I'm planning it out the following: Select all distinct ip addresses Loop through them all saying count(id) where IP='{ip}' and storing the count List the top five counts. Downsides include what if I have 500 ip addresses. That's 500 queries I have to run to figure out what are the top five. I'd like to build a query like so select ip from table where 1 order by count({distinct ip}) asc limit 5

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• Bind a users role to dropdown?

  - by Dynde

  Hi... I'm trying to bind a selected user's role to a dropdown-list. The purpose of this is to be able to change said user's role. I'm attempting this inside a formview hooked up to a linqdatasource which contains a row from the aspnet_User table. The dropdown list is hooked up to a linqdatasource of all the roles in the aspnet_Roles table (with DataValueField="RoleID", DataTextField="RoleName"). I figured it would be possible with something like: SelectedValue='<%# Bind("aspnet_UsersInRole[0].aspnet_Role.RoleID") %>' But this throws a parser exception, about the bind call not being correctly formatted. The roles are there, they show up when I remove the "SelectedValue" Can anyone point me in the right direction?

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