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• Find model records by ID in the order the array of IDs were given

  - by defaye

  I have a query to get the IDs of people in a particular order, say: ids = [1, 3, 5, 9, 6, 2] I then want to fetch those people by Person.find(ids) But they are always fetched in numerical order, I know this by performing: people = Person.find(ids).map(&:id) => [1, 2, 3, 5, 6, 9] How can I run this query so that the order is the same as the order of the ids array? I made this task more difficult as I wanted to only perform the query to fetch people once, from the IDs given. So, performing multiple queries is out of the question. I tried something like: ids.each do |i| person = people.where('id = ?', i) But I don't think this works.

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• comparing two cursors in oracle instead of using MINUS

  - by Omnipresent

  The following query takes more than 3 minutes to run because tables contain massive amounts of data: SELECT RTRIM(LTRIM(A.HEAD)), A.EFFECTIVE_DATE, FROM TABLE_1 A WHERE A.TYPE_OF_ACTION='6' AND A.EFFECTIVE_DATE >= ADD_MONTHS(SYSDATE,-15) MINUS SELECT RTRIM(LTRIM(B.head)), B.EFFECTIVE_DATE, FROM TABLE_2 B In our system a query gets killed if it is running for more than 8 seconds. Is there a way to run the queries individually ..put them in cursors..compare and then get the results? that way each query will be ran individually rather than as one massive query which takes 3 minutes. How would two cursors be compared to mimic the MINUS?

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• nth smallest number among two databases of size n each using divide and conquer

  - by urfriend

  we have two databases of size n containing numbers without repeats. So, in total we have 2n elements. They can be accessed through a query to one database at a time. The query is such that you give it a k and it returns kth smallest entry in that database. we need to find nth smallest entry among all the 2n elements in O(logn) queries. the idea is to use divide and conquer but i need some help thinking through this. thanks!

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• What are the pros and cons to keeping SQL in Stored Procs versus Code

  - by Guy

  What are the advantages/disadvantages of keeping SQL in your C# source code or in Stored Procs? I've been discussing this with a friend on an open source project that we're working on (C# ASP.NET Forum). At the moment, most of the database access is done by building the SQL inline in C# and calling to the SQL Server DB. So I'm trying to establish which, for this particular project, would be best. So far I have: Advantages for in Code: Easier to maintain - don't need to run a SQL script to update queries Easier to port to another DB - no procs to port Advantages for Stored Procs: Performance Security

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• HSM - cryptoki - opening sessions overhead

  - by Raj

  I am having a query regarding sessions with HSM. I am aware that there is an overhead if you initialise and finalise the cryptoki api for every file you want to encrypt/decrypt. My queries are, Is there an overhead in opening and closing individual sessions for every file, you want to encrypt/decrypt.(C_Initialize/C_Finalize) How many maximum number of sessions can i have for a HSM simultaneously, with out affecting the performance? Is opening and closing the session for processing individual files the best approach or opening a session and processing multiple files and then closing the session the best approach? Thanks

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• How can I enable MySQL's slow query log without restarting MySQL?

  - by mmattax

  I followed the instructions here: http://crazytoon.com/2007/07/23/mysql-changing-runtime-variables-with-out-restarting-mysql-server/ but that seems to only set the threshold. Do I need to do anything else like set the filepath? According to MySQL's docs If no file_name value is given for --log-slow-queries, the default name is host_name-slow.log. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. Running SHOW VARIABLES doesn't indicate any log file path and I don't see any slow query log file on my server...

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• Mysqld Crashes immediately on running on Windows 7...?

  - by Cyril Gupta

  I am trying to run MySql 5.1 on Windows 7 Home Premium 64 bit. I have downloaded the MSI installer from the MYSql website and installed it. The installation is successful, but the service does not start. If I try to run MySql manually using the mysqld executable, it crashes immediately on running (error: mysqld.exe has stopped working). Earlier mysql was running on the machine, but I had some problem with it (wasn't executing big queries) and installed it again which somehow broke the program. I had installed it to work as a service which started giving me this isse, and now it won't work even if I don't install it as a service. I have tried removing the mysql folder and re-installing. Is there somewhere else where Mysql saves configuration info or other data? Has anyone else found this problem and solved it? How can I find out why the process is failing to run?

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• How does mysql define DISTINCT()

  - by goran

  AFAIK SQL defines two uses of DISTINCT keywords - SELECT DISTINCT field... and SELECT COUNT(DISTINCT field) ... However in one of web applications that I administer I've noticed performance issues on queries like SELECT DISTINCT(field1), field2, field3 ... DISTINCT() on a single column makes no sense and I am almost sure it is interpreted as SELECT DISTINCT field1, field2, field3 ... but how can I prove this? I've searched mysql site for a reference on this particular syntax but could not find any. Does anyone have a link to definition of DISTINCT() in mysql or knows about other authoritative source on this? Best

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• Resources to learn about engineering aspects of data analytics (OLAP, warehousing, ETL, etc.)

  - by JT

  I'm a math/stats guy, interested in learning more about the engineering aspects of "data analytics" (this may be an overly broad term, this is a case of "I don't know what I don't know", so I'm not sure how to be more specific). I'm fine with manipulating and analyzing the data once it's already stored somewhere and I can access it, and I'm fine with writing scripts and SQL queries (and have a general knowledge of things like normalization). What I don't know is the whole engineering process of capturing and storing the data. For example, terms I've heard thrown about that I only vaguely understand the meaning of include: - OLAP, OLTP - Data warehousing - ETL - ??? What's a good book (or any other resource) to learn about these kinds of things? What are things I should know about database design (normalization seems kinda "obvious" to me, something I would have done even before I knew the term -- is there anything else?)? In other words, for jobs falling under the umbrella term of "analytics engineer", what kinds of things should I know?

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• WSSQL query for multiple computers at once

  - by Josh

  I can run normal searches just fine. Windows 7 won't let me add a network share to my local index, but I can query the remote index just fine. The problem is that I can't find a way to query two indexes at once. I was hoping that something like this would work: SELECT System.ItemName FROM compA.SystemIndex, compB.SystemIndex WHERE SCOPE='file://compA/pathA' OR SCOPE='file://compB/pathB' but it doesn't. For simple queries, I can query compA and compB separately and then merge the results myself, but I'm hoping for a better way. Anybody here have some experience with this?

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• Can Entity Framework be used for the purpose of entity/schema definition at application runtime?

  - by Kabeer

  Hello. Can 'Entity Framework' be used for the purpose of entity definition at application runtime? Ok, to make it simple, here is what I want to achieve: My application is a product. I should be able to define entities at runtime on the basis of inputs gathered from an 'authoring' user (in effect this means 'model first' approach). These entities are of course persistable. Further, after having defined the entities and their relationships, I should be able to make complex queries across them for many reasons, including reports. Is the above possible and how? So far what I have realized is that there is a dependency on Visual Studio.

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• MySQL Insert not working with Date column

  - by Ian McCullough

  Hello All, I am having an issue with a simple insert query into a table. I have this PHP Code $T_MEMBER = "INSERT INTO T_MEMBER (MEMBER_IDENTIFIER,LAST_NAME,FIRST_NAME,BIRTH_DATE) VALUES ('$memberID','$last','$first','$birthdate')"; mysql_query($T_MEMBER) or die(mysql_error()); Here are a few examples of what the query looks like if i echo it: INSERT INTO T_MEMBER (MEMBER_IDENTIFIER,LAST_NAME,FIRST_NAME,BIRTH_DATE) VALUES ('2007','Hayes','Karin','1958-30-10') INSERT INTO T_MEMBER (MEMBER_IDENTIFIER,LAST_NAME,FIRST_NAME,BIRTH_DATE) VALUES ('2020','Long','Peggy','1968-29-5') INSERT INTO T_MEMBER (MEMBER_IDENTIFIER,LAST_NAME,FIRST_NAME,BIRTH_DATE) VALUES ('2021','Torres','Diane','1968-30-8') BIRTH_DATE is a date type column. The problem is, after i do any of these queries, the date shows up as 000-00-00!!!! I have been wracking my brain and i cannot seem to find the issue. Thanks, Ian

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• "Access is denied" error on accessing iframe document object

  - by Ovesh

  For posting AJAX forms in a form with many parameters, I am using a solution of creating an iframe, posting the form to it by POST, and then accessing the iframe's content. specifically, I am accessing the content like this: $("some_iframe_id").get(0).contentWindow.document I tested it and it worked. On some of the pages, I started getting an "Access is denied" error. As far as I know, this shouldn't happen if the iframe is served from the same domain. I'm pretty sure it was working before. Anybody have a clue? If I'm not being clear enough: I'm posting to the same domain. So this is not a cross-domain request. I am testing on IE only. P.S. I can't use simple ajax POST queries (don't ask...)

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• Oracle - Is there any effects of not having a primary key on a table ?

  - by Sathya

  We use sequence numbers for primary keys on the tables. There are some tables where we dont really use the primary key for any querying purpose. But, we have Indexes on other columns. These are non-unique indexes. The queries use these non-primary key columns in the WHERE conditions. So, I dont really see any benefit of having a primary key on such tables. My experience with SQL 2000 was that, it used to replicate tables which had some primary key. Otherwise it would not. I am using Oracle 10gR2. I would like to know if there are any such side-effects of having tables that dont have primary key.

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• Find all clauses related to an atom

  - by Luc Touraille

  This is probably a very silly question (I just started learning Prolog a few hours ago), but is it possible to find all the clauses related to an atom? For example, assuming the following knowledge base: cat(tom). animal(X) :- cat(X). , is there a way to obtain every possible information about tom (or at least all the facts that are explicitly stated in the base)? I understand that a query like this is not possible: ?- Pred(tom). so I thought I could write a rule that would deduce the correct information: meta(Object, Predicate) :- Goal =.. [Predicate, Object], call(Goal). so that I could write queries such as ?- meta(tom, Predicate). but this does not work because arguments to call are not sufficiently instantiated. So basically my question is: is this at all possible, or is Prolog not design to provide this kind of information? And if it is not possible, why?

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• Catching constraint violations in JPA 2.0.

  - by Dennetik

  Consider the following entity class, used with, for example, EclipseLink 2.0.2 - where the link attribute is not the primary key, but unique nontheless. @Entity public class Profile { @Id private Long id; @Column(unique = true) private String link; // Some more attributes and getter and setter methods } When I insert records with a duplicate value for the link attribute, EclipseLink does not throw a EntityExistsException, but throws a DatabaseException, with the message explaining that the unique constraint was violated. This doesn't seem very usefull, as there would not be a simple, database independent, way to catch this exception. What would be the advised way to deal with this? A few things that I have considered are: Checking the error code on the DatabaseException - I fear that this error code, though, is the native error code for the database; Checking the existence of a Profile with the specific value for link beforehand - this obviously would result in an enormous amount of superfluous queries.

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• Recursive query question - break rows into columns?

  - by Stew

  I have a table "Families", like so FamilyID PersonID Relationship ----------------------------------------------- F001 P001 Son F001 P002 Daughter F001 P003 Father F001 P004 Mother F002 P005 Daughter F002 P006 Mother F003 P007 Son F003 P008 Mother and I need output like FamilyID PersonID Father Mother ------------------------------------------------- F001 P001 P003 P004 F001 P002 P003 P004 F001 P003 F001 P004 F002 P005 P006 F002 P006 F003 P007 P008 F003 P008 In which the PersonID of the Father and Mother for a given PersonID are listed (if applicable) in separate columns. I know this must be a relatively trivial query to write (and therefore to find instructions for), but I can't seem to come up with the right search terms. Searching "SQL recursive queries" has gotten me closest, but I can't quite translate those methods to what I'm trying to do here. I'm trying to learn, so multiple methods are welcome, as is vocabulary I should read up on. Thanks!

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• Safe HttpContext.Current.Cache Usage

  - by Burak SARICA

  Hello there, I use Cache in a web service method like this : var pblDataList = (List<blabla>)HttpContext.Current.Cache.Get("pblDataList"); if (pblDataList == null) { var PBLData = dc.ExecuteQuery<blabla>( @"SELECT blabla"); pblDataList = PBLData.ToList(); HttpContext.Current.Cache.Add("pblDataList", pblDataList, null, DateTime.Now.Add(new TimeSpan(0, 0, 15)), Cache.NoSlidingExpiration, CacheItemPriority.Normal, null); } I wonder is it thread safe? I mean the method is called by multiple requesters And more then one requester may hit the second line at the same time while the cache is empty. So all of these requesters will retrieve the data and add to cache. The query takes 5-8 seconds. May a surrounding lock statement around this code prevent that action? (I know multiple queries will not cause error but i want to be sure running just one query.)

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• PDO update query with conditional?

  - by dmontain

  I have a PDO mysql that updates 3 fields. $update = $mypdo->prepare("UPDATE tablename SET field1=:field1, field2=:field2, field3=:field3 WHERE key=:key"); But I want field3 to be updated only when $update3 = true; (meaning that the update of field3 is controlled by a conditional statement) Is this possible to accomplish with a single query? I could do it with 2 queries where I update field1 and field2 then check the boolean and update field3 if needed in a separate query. //run this query to update only fields 1 and 2 $update_part1 = $mypdo->prepare("UPDATE tablename SET field1=:field1, field2=:field2 WHERE key=:key"); //if field3 should be update, run a separate query to update it separately if ($update3){ $update_part2 = $mypdo->prepare("UPDATE tablename SET field3=:field3 WHERE key=:key"); } But hopefully there is a way to accomplish this in 1 query?

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• Freebase Query with "JOINS"

  - by codemonkey

  ... Yeah, yeah, I know traditional joins don't exist. I actually like the freebase query methodology in theory, just having a little trouble getting it to actually work for me : ) Anyone have a dumb-simple example of getting Freebase data via MQL that pulls from two different "tables"? In particular, I'm trying to get automotive data... so for example, pulling fields from both /automotive/model_year and /automotive/trim_year. I've read the documentation (for hours actually). There's a distinct possibility that I'm looking right at such an example somewhere and just not seeing it because my OLTP brain just doesn't comprehend what it's seeing. * Note * ... that the two "types" I'm working with above are siblings, not parent/child. Does freebase even allow joining data between sibling nodes... I see examples of queries pulling from parent/child, but not from siblings I don't think (or I've overlooked them).

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• Reversing column values in mysql command line

  - by user94154

  I have a table posts with the column published, which is either 0 (unpublished) or 1 (published). Say I want to make all the published posts into unpublished posts and all the unpublished posts into published posts. I know that running UPDATE posts SET published = 1 WHERE published = 0; UPDATE posts SET published = 0 WHERE published = 1; will end up turning all my posts into published posts. How can I run these queries in the mysql command line so that it truly "reverse" the values, as opposed to the mistake outlined above? Thanks

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• Dealing w/ Sqlite Join results in a cursor

  - by Bill

  I have a one-many relationship in my local Sqlite db. Pretty basic stuff. When I do my left outer join I get back results that look like this: the resulting cursor has multiple rows that look like this: A1.id | A1.column1 | A1.column2 | B1.a_id_fk | B1.column1 | B1.column2 A1.id | A1.column1 | A1.column2 | B2.a_id_fk | B2.column1 | B2.column2 and so on... Is there a standard practice or method of dealing with results like this ? Clearly there is only A1, but it has many B-n relationships. I am coming close to using multiple queries instead of the "relational db way". Hopefully I am just not aware of the better way to do things. I intend to expose this query via a content provider and I would hate for all of the consumers to have to write the same aggregation logic.

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• Using Excel To Read Access Without MS Access On Computer

  - by Tom Clark

  I have written code that joins two table in access, using criteria supplied from drop down lists in excel and then returns the data to a specific location on the spreadsheet (titles already on the sheet). This works fine on my box and others with MS Access on the machine, but the purpose of writing this was to give people (associates) that dont have the MS Access on their machines (which is most of them) to be able to do simple queries to the database. When we try to run this on a machine without MS Access, we are getting the error message "Compile Error: Cant find project or library." Since this works fine on any machine so far that has Access, but not the others I am wondering if this is not possible without the actual Access software. Any help or insight would be appreciated. Tom

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• Does the optimizer filter subqueries with outer where clauses

  - by Mongus Pong

  Take the following query: select * from ( select a, b from c UNION select a, b from d ) where a = 'mung' Will the optimizer generally work out that I am filtering a on the value 'mung' and consequently filter mung on each of the queries in the subquery. OR will it run each query within the subquery union and return the results to the outer query for filtering (as the query would perhaps suggest) In which case the following query would perform better : select * from ( select a, b from c where a = 'mung' UNION select a, b from d where a = 'mung' ) Obviously query 1 is best for maintenance, but is it sacrificing much performace for this? Which is best?

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• Do you use enums in your data applications and how?

  - by Ivan

  My practice shows that a general enterprise application has a lot of entities which's nature corresponds to an elementary enumeration. For example We may have an Order entity which may have such fields as "OrderType", "OrderStatus", "Currency", etc. referencing corresponding Entities which are nothing more than just a textual name bound to a key to be referenced. Using enums would look very natural here. But entities have to be defined in application code at design-time, am I right? While in we need to be able to CRUD enum value variants at runtime and use enums in server-side SQL queries (like stored procedures and views). What are you practices and thoughts on this subject? I am particularly interested in C#4, linq and T-SQL.

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