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• How does linq decide between inner & outer joins

  - by user287795

  Hi Usually linq is using an left outer join for its queries but on some cases it decides to use inner join instead. I have a situation where that decision results in wrong results since the second table doesn't always have suitable records and that removes the records from the first table. I'm using a linqdatasource over a dbml where the relevant tables are identical but one holds historical records removed from the first. both have the same primary key. and I'm using a dataloadoption to load both tables at once with out round trips. Would you explain why linq decided to use an inner join here? Thanks

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• select records from table in the order in which i inserted

  - by echo

  consider a tale is as follows, EmployeeId | Name | Phone_Number Now, i insert 10 records... When i query them back, select * from myTable they are not selected in the order i inserted. I can obviously keep an autoincrement index and ORDER BY index. But i dont want to alter the table. How can i do this without altering the table?

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• How can I synchronize one set of data with another?

  - by RenderIn

  I have an old database and a new database. The old records were converted to the new database recently. All our old applications continue to point to the old database, but the new applications point to the new database. Currently the old database is the only one being updated, so throughout the day the new database becomes out of sync. It is acceptable for the new database to be out of sync for a day, so until all our applications are pointed to the new database I just need to write a nightly cron job that will bring it up to date. I do not want to purge the new database and run the complete conversion script each night, as that would reduce uptime and would create a mess in our auditing of that table. I'm thinking about selecting all the data from the old database, converting it to the new database structure in memory, and then checking for the existence of each record before inserting it in the new database. After that's done, I'd select everything from the new database and check if it exists in the old one, and if not delete it. Is this the simplest way to do this?

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• Select where a value present

  - by Roy

  First a database example: id, product_id, cat, name, value -------------------------------- 1,1,Algemeen,Processor,2 Ghz 2,1,Algemeen,Geheugen,4 GB 3,2,Algemeen,Processor,3 Ghz 4,2,Algemeen,Geheugen,4 GB 5,3,Beeldscherm,Inch,22" 6,3,Beeldscherm,Kleur,Zwart 7,3,Algemeen,Geheugen,3 GB 8,3,Algemeen,Processor,3 Ghz I want with one query to select the follow id's: 1,2,3,4,7,8 Because the cat = algemeen and the name = processor by these products. ID 5,6 are only present by product 3. So, the entry's (cat and name) which are present by all products (product_id) have to be selected. The database contains 80.000 entry's with a lot of diffrent cat's, name's and value's. Is this possible with one query or is some php necessary? How do I do this? My apologies for the bad English.

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• Combine First, Middle Initial, Last name and Suffix in T-SQL (No extra spaces)

  - by Paul

  I'm trying not to reinvent the wheel here...I have these four fields [tbl_Contacts].[FirstName], [tbl_Contacts].[MiddleInitial], [tbl_Contacts].[LastName], [tbl_Contacts].[Suffix] And I want to create a FullName field in a view, but I can't have extra spaces if fields are blank...So I can't do FirstName + ' ' + MiddleInitial + ' ' + LastName + ' ' + Suffix...Because if there is no middle initial or suffix I'd have 2 extra spaces in the field. I think I need a Case statement, but I thought someone would have a handy method for this...Also, the middleinitial and suffix may be null.

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• Database table schema design - varchar(n). Suitable choice of N

  - by morpheous

  Coming from a C background, I may be getting too anal about this and worrying unnecessarily about bits and bytes here. Still, I cant help thinking how the data is actually stored and that if I choose an N which is easily factorizable into a power of 2, the database will be more effecient in how it packs data etc. Using this "logic", I have a string field in a table which is a variable length up to 21 chars. I am tempted to use 32 instead of 21, for the reason given above - however now I am thinking that I am wasting disk space because there will be space allocated for 11 extra chars that are guaranteed to be never used. Since I envisage storing several tens of thousands of rows a day, it all adds up. Question: Mindful of all of the above, Should I declare varchar(21) or varchar(32) and why?

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• PHP, MySQL - would results-array shuffle be quicker than "select... order by rand()"?

  - by sombe

  I've been reading a lot about the disadvantages of using "order by rand" so I don't need update on that. I was thinking, since I only need a limited amount of rows retrieved from the db to be randomized, maybe I should do: $r = $db->query("select * from table limit 500"); for($i;$i<500;$i++) $arr[$i]=mysqli_fetch_assoc($r); shuffle($arr); (i know this only randomizes the 500 first rows, be it). would that be faster than $r = $db->("select * from table order by rand() limit 500"); let me just mention, say the db tables were packed with more than...10,000 rows. why don't you do it yourself?!? - well, i have, but i'm looking for your experienced opinion. thanks!

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• select distinct over specific columns

  - by Midhat

  A query in a system I maintain returns QID AID DATA 1 2 x 1 2 y 5 6 t As per a new requirement, I do not want the (QID, AID)=(1,2) pair to be repeated. We also dont care what value is selected from "data" column. either x or y will do. What I have done is to enclose the original query like this SELECT * FROM (<original query text>) Results group by QID,AID Is there a better way to go about this? The original query uses multiple joins and unions and what not, So I would prefer not to touch it unless its absolutely necesary

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• what is the 'extra' mean in this django code..

  - by zjm1126

  TOPIC_COUNT_SQL = """ SELECT COUNT(*) FROM topics_topic WHERE topics_topic.object_id = maps_map.id AND topics_topic.content_type_id = %s """ MEMBER_COUNT_SQL = """ SELECT COUNT(*) FROM maps_map_members WHERE maps_map_members.map_id = maps_map.id """ maps = maps.extra(select=SortedDict([ ('member_count', MEMBER_COUNT_SQL), ('topic_count', TOPIC_COUNT_SQL), ]), select_params=(content_type.id,)) i don't know this mean, thanks

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• need to read data from oracle database with many conditions

  - by randeepsp

  hi! i have 3 tables A,B and C. table A has column employee_name,id table B is the main table and has columns id,os version. table c has the columns id,package id and package version. i want to query the count of employee_name where the id of table a and c are matched with id of table b(which is the main table). i should also get the names of employees grouped by the os version they have and also the package version.

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• Desgining a database with flexible user profile

  - by Mughrabi

  Hi, Am working on a design where I can have flexible attributes for a user & am confused how to continue the design of the schema. I made a table where I kept system needed information called users id username password Now, I wish to create a profile table and have one to one relation where all the other attributes in profile table such as email, first name, last name..etc. My question is, is there a way to add a third table in which even profile will be flexible if my clients need to create a new attribute he/she won't need any customization to the code? Regards,

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• Copying Primary key to another field in Access.

  - by BashLover

  Hey, I'm struggling to copy the Primary Key to another field in Access. This is irrelevant , but clarifying on what I'm comparing. ... WHERE Tunniste=" & [Tarkiste] & "" Tunniste = Primary Key , Autonumber , ID (Generated by Access.) Tarkiste = This is the field I want to copy it to compare it. I'm open to suggestions, I've already try'ed with Form_Load, using the following code. Private Sub Form_Load() DoCmd.RunSQL "UPDATE Korut SET [Tarkiste]=('" & Tunniste & "');" End Sub But this copied the same key to all the entries in "Tarkiste" field. In simplicity I want 1:1 copy of field "Tunniste" to "Tarkiste" , whichever method it takes. Started from this question. File Picker Replaces All Rows With The Same Choice.

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• Greatest not null column

  - by Álvaro G. Vicario

  I need to update a row with a formula based on the largest value of two DATETIME columns. I would normally do this: GREATEST(date_one, date_two) However, both columns are allowed to be NULL. I need the greatest date even when the other is NULL (of course, I expect NULL when both are NULL) and GREATEST() returns NULL when one of the columns is NULL. This seems to work: GREATEST(COALESCE(date_one, date_two), COALESCE(date_two, date_one)) But I wonder... am I missing a more straightforward method?

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• how to pull and display range (min-max) data for each page in pagination?

  - by Ty W

  I have a table of data that is searchable and sortable, but likely to produce hundreds or thousands of results for broad searches. Assuming the user searches for "foo" and sorts the foos in descending price order I'd like to show a quick-jump select menu like so: <option value="1">Page 1 ($25,000,000 - $1,625,000)</option> <option value="2">Page 2 ($1,600,000 - $1,095,000)</option> <option value="3">Page 3 ($1,095,000 - $815,000)</option> <option value="4">Page 4 ($799,900 - $699,000)</option> ... Is there an efficient way of querying for this information directly from the DB? I've been grabbing all of the matching records and using PHP to calculate the min and max value for each page which seems inefficient and likely to cause scaling problems. The only possible technique I've been able to come up with is some way of having a calculated variable that increments every X records (X records to a page), grouping by that, and selecting MIN/MAX for each page grouping... unfortunately I haven't been able to come up with a way to generate that variable.

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• vb.net checkboxes. Need to populate from database and also help in designing

  - by redr

  i have this requirement and since im new to vb.net dont really have much of idea how to do this. I have 20 checkboxes with dropdowns and textbox with it. the example is - table tr td checkbox -- textbox -- dropdownlist /td /tr tr td chk1 txtbox1 ddl1 /td /tr tr td chk2 txtbox2 ddl2 /td /tr and so on. the above structure shall be in one row of a table. does anyone know how to design this in code recursive and also how to take the checkbox data from here and send it to db table for records insert, update and select. thanks

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• One on One table relation - is it harmful to keep relation in both tables?

  - by EBAGHAKI

  I have 2 tables that their rows have one on one relation.. For you to understand the situation, suppose there is one table with user informations and there is another table that contains a very specific informations and each user can only link to one these specific kind of informations ( suppose second table as characters ) And that character can only assign to the user who grabs it, Is it against the rules of designing clean databases to hold the relation key in both tables? User Table: user_id, name, age, character_id Character Table: character_id, shape, user_id I have to do it for performance, how do you think about it?

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• MySQL - accessing a table sum and compare to another table?

  - by assignment_operator

  This is for a homework assignment. I just plain don't understand how to do it. The instructions for this particular question is: List the branch name for all branches that have at least one book that has at least 4 copies on hand. Where the tables in question are: Branch: BranchName | BranchId Henry Downtown | 1 16 Riverview | 2 Henry On The Hill | 3 Inventory: BookId | BranchId | OnHand 1 | 1 | 2 2 | 3 | 4 3 | 1 | 8 4 | 3 | 1 5 | 1 | 2 6 | 2 | 3 From what I understand, I can get the number of OnHand per branch name with: SELECT BranchName, SUM(OnHand) FROM Branch B, Inventory I WHERE B.BranchId = I.BranchId GROUP BY BranchName; but I don't get how I'd do the comparison between the sum of OnHand per branch and 4. Any help would be appreciated, guys!

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• primary key is automatically indexed?

  - by every_answer_gets_a_point

  is it true that in mysql the primary key is automatically indexed?

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• How effecient is a details table?

  - by Jeffrey Lott

  At my job, we have pseudo-standard of creating one table to hold the "standard" information for an entity, and a second table, named like 'TableNameDetails', which holds optional data elements. On average, for every row in the main table will have about 8-10 detail rows in it. My question is: What kind of performance impacts does this have over adding these details as additional nullable columns on the main table?

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• Is there any optimizations I can do with this statement to get the count of used rows?

  - by RPS

  Is there any optimizations I can do with this statement to get the count of used rows. Note: The ProductOrderInfo table has over 40 million rows in it. SELECT @TotalUsed = COUNT(*) FROM ProductInfo WITH (NOLOCK) WHERE ProductInfoId IN ( SELECT ProductInfoId FROM ProductOrderInfo WITH (NOLOCK) );

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• Timeout not working in SQL Connection

  - by carlos

  I have this simple code to test that a DB is ready: Function testlocalcon() As Boolean Dim constr As String = _clconstr Try Using t As New SqlConnection() constr = constr & " ; Connect Timeout=1" If Not t.State = Data.ConnectionState.Open Then t.ConnectionString = constr t.Open() If t.State = Data.ConnectionState.Open Then Return True Else Return False End If Else Return True End If End Using Catch ex As Exception Return False End Try End Function I do not want to execute a query, just to check the connection, but no matter what the time out parameter is ignored. I search here (Stackoverflow) and internet and found nothing in how to fix this. Any one else have this problem? Or, are there any other ideas on how to let the application know that the DB is ready?

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• Help with query in Microsoft Access

  - by Gold

  I have 2 tables: Table A: code | name Table B: barcode | name Table B has full barcode and name, Table A has only code. I need to run update query that fill name in Table A. I tried something like: update A set name = (select top 1 Name from B where B.Code = mid(A.Barcode,1,8)) but it doesn't work.

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• How do I specify a default value in a MS Access query?

  - by jheddings

  I have three tables similar to the following: tblInvoices: Number | Date | Customer tblInvDetails: Invoice | Quantity | Rate | Description tblPayments: Invoice | Date | Amount I have created a query called exInvDetails that adds an Amount column to tblInvDetails: SELECT tblInvDetails.*, [tblInvDetails.Quantity]*[tblInvDetails.Rate]* AS Amount FROM tblInvDetails; I then created a query exInvoices to add Total and Balance columns to tblInvoices: SELECT tblInvoices.*, (SELECT Sum(exInvDetails.Amount) FROM exInvDetails WHERE exInvDetails.Invoice = tblInvoices.Number) AS Total, (SELECT Sum(tblPayments.Amount) FROM tblPayments WHERE tblPayments.Invoice = tblInvoices.Number) AS Payments, (Total-Payments) AS Balance FROM tblInvoices; If there are no corresponding payments in tblPayments, the fields are null instead of 0. Is there a way to force the resulting query to put a 0 in this column?

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• mysql NO_AUTO_VALUE_ON_ZERO problem

  - by every_answer_gets_a_point

  at least i think that is what the problem is. i am updating a mysql database through excel using an odbc like this: 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 besides the fields above, i also have a primary key auto_increment field called rowid for some reason the only field that gets updated is instrument. none of the other fields get updated.. however, when i try to do the same updating on a table that has no ROWID auto_increment field, it works perfectly has anyone else experienced this kind of issue before?

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• Does UNIQ constraint mean also an index on that field(s)?

  - by Gremo

  As title, should i defined a separate index on email column (for searching purposes) or the index is "automatically" added along with UNIQ_EMAIL_USER constraint? CREATE TABLE IF NOT EXISTS `customer` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(11) NOT NULL, `first` varchar(255) NOT NULL, `last` varchar(255) NOT NULL, `slug` varchar(255) NOT NULL, `email` varchar(255) NOT NULL, `created_at` datetime NOT NULL, `updated_at` datetime NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `UNIQ_SLUG` (`slug`), UNIQUE KEY `UNIQ_EMAIL_USER` (`email`,`user_id`), KEY `IDX_USER` (`user_id`) ) ENGINE=InnoDB;

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