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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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• Ruby ways to authenticate using headers?

  - by webdestroya

  I am designing an API system in Ruby-on-Rails, and I want to be able to log queries and authenticate users. However, I do not have a traditional login system, I want to use an APIkey and a signature that users can submit in the HTTP headers in the request. (Similar to how Amazon's services work) Instead of requesting /users/12345/photos/create I want to be able to request /photos/create and submit a header that says X-APIKey: 12345 and then validate the request with a signature. Are there any gems that can be adapted to do that? Or better yet, any gems that do this without adaptation? Or do you feel that it would be wiser to just have them send the API key in each request using the POST/GET vars?

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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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• search engine crawling frequency

  - by Aditya Pratap Singh

  I want to design a search engine for news websites ie. download various article pages from these websites, index the pages, and answer search queries on the index. I want a short pseudocode to find an appropriate crawling frequency -- i do not want to crawl too often because the website may not have changed, and do not want to crawl too infrequently because index would then be out of date. Assume that crawling code looks as follows while(1) { sleep(sleep_interval); // sleep for sleep_interval crawl(website); // crawls the entire website diff = diff(currently_crawled_website, previously_crawled_website); // returns a % value of difference between the latest and previous crawls of the website sleep_interval = infer_sleep_interval(diff, sleep_interval); } looking for a pseudocode for the infer_sleep_interval method: long sleep_interval infer_sleep_interval(int diff_percentage,long previous_sleep_interval) { ... ... ... } i want to design method which adaptively alters the sleeping interval based on the update frequency of the website.

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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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• 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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• 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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• 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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• how to create a subquery in sql using count based on outer query

  - by user1754716

  I hope someone can help me with this query. Basically I have two queries that I want to "combine". I want the second query as an extra column along with the first query. The first one is this : SELECT t_Item_Storage_Location.Storage_Loc_Nbr, t_Storage_Location.Storage_Loc_Type_Code, Count(t_Load.Load_Id) AS CurrentLoadCount, t_load.MMM_Id_Nbr FROM t_Load INNER JOIN (t_Storage_Location INNER JOIN t_Item_Storage_Location ON t_Storage_Location.Storage_Loc_Nbr = t_Item_Storage_Location.Storage_Loc_Nbr) ON (t_Load.Storage_Loc_Nbr = t_Item_Storage_Location.Storage_Loc_Nbr) AND (t_Load.MMM_Id_Nbr = t_Item_Storage_Location.MMM_Id_Nbr) where ((((t_Item_Storage_Location.MMM_Id_Nbr) Between '702004%' And '702011%') AND ((t_Item_Storage_Location.Storage_Loc_Nbr) Like '%A') AND ((t_Storage_Location.Storage_Loc_Type_Code)='CD') AND ((t_Load.Active_Status_Ind)='A') AND ((t_Load.QC_Status_Code) Like 'R%') AND ((t_Load.MMM_Facility_Code)='MC')) OR (((t_Item_Storage_Location.Storage_Loc_Nbr) Like '%B')) OR (((t_Item_Storage_Location.Storage_Loc_Nbr) Like '%C')) OR (((t_Item_Storage_Location.Storage_Loc_Nbr) Like '%D')) OR (((t_Item_Storage_Location.Storage_Loc_Nbr) Like '%E')) ) GROUP BY t_Item_Storage_Location.MMM_Id_Nbr, t_Item_Storage_Location.Storage_Loc_Nbr, t_Storage_Location.Storage_Loc_Type_Code, t_Load.MMM_Facility_Code, t_load.MMM_Id_Nbr HAVING Count(t_Load.Load_Id)<4 The second one, is based on the t_load.MMM_Id_Nbr of the first one. Basically I want a count of all the loads with that mmm_id_nbr. SELECT count(Load_ID) as LoadCount, MMM_Id_Nbr, storage_Loc_Nbr FROM t_load WHERE QC_Status_Code like 'R%' and mmm_Facility_Code ='MC' and Active_Status_Ind='A' GROUP by MMM_Id_Nbr, storage_loc_Nbr

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• Query DNSBL or other block lists using PHP

  - by 55skidoo

  Is there any way to use PHP code to query a DNSBL (block list) provider and find out if the IP address submitted is a bad actor? I would like to take an existing IP address out of a registration database, then check whether it's a known block-listed IP address by performing a lookup on it, then if it's a blacklisted, do an action on it (such as, delete entry from registration database). Most of the instructions I have seen assume you are trying to query the blocklist via a mail server, which I can't do. I tried querying via web browser by typing in queries such as "58.64.xx.xxx.dnsbl.sorbs.net" but that didn't work.

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• Given GPS coordinates, how do I find nearby landmarks or points-of-interest?

  - by stackoverflowuser2010

  I just bought a Google Nexus One smartphone, and I want to write a small Android application for fun. Suppose I can get my current GPS coordinates, so then how can I programmatically find nearby landmarks or points-of-interest within some radius? Is there an API to get GPS geo-tagged landmarks, like in Google Earth's database? For example, if I'm in downtown Chicago, my program would point me to all the "tourist" things to visit in that city. Ideally, it would all run on my smartphone, but if necessary, I can have the smartphone query a webserver, which would then run more queries.

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• make multiple, composite query in oracle

  - by Meloun

  How can i make multiple, composite query in oracle? for example this several queries in one step? 1 CREATE TABLE test (id NUMBER PRIMARY KEY, name VARCHAR2(30)); 2 CREATE SEQUENCE test_sequence START WITH 1 INCREMENT BY 1; 3 CREATE OR REPLACE TRIGGER test_trigger BEFORE INSERT ON test REFERENCING NEW AS NEW FOR EACH ROW BEGIN SELECT test_sequence.nextval INTO :NEW.ID FROM dual; END; 4 INSERT INTO test (name) VALUES ('Jon'); 5 INSERT INTO test (name) VALUES ('Meloun');

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• Help me understand Rails eager loading

  - by aaronrussell

  I'm a little confused as to the mechanics of eager loading in active record. Lets say a Book model has many Pages and I fetch a book using this query: @book = Book.find book_id, :include => :pages Now this where I'm confused. My understanding is that @book.pages is already loaded and won't execute another query. But suppose I want to find a specific page, what would I do? @book.pages.find page_id # OR... @book.pages.to_ary.find{|p| p.id == page_id} Am I right in thinking that the first example will execute another query, and therefore making the eager loading pointless, or is active record clever enough to know that it doesn't need to do another query? Also, my second question, is there an argument that in some cases eager loading is more intensive on the database and sometimes multiple small queries will be more efficient that a single large query? Thanks for your thoughts.

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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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• Looking for an elegant way to store one-to-many relationship in coredata when order is important

  - by Eric Schweichler

  I've been trying to come up with a way to solve my problem, but every solution I can think of is messy and makes me want to retch. I have a one-to-many relationship, consisting of a Team object that can have many Member objects. When I built my data model using Xcode, I was given the default NSSet in which to store the member objects, Unfortunately Sets are not ordered and I need to preserve the order of the Member objects and I need to know if there are empty spaces between Members. I thought of Using an NSArray in place of the NSSet and creating a dummy Member object in my data store that I could use to mark vacant a spot between to Member objects, but that solution really feels like too much of a hack to me. Since I'll always have to filter out this dummy Member from any queries. An NSDictionary would be perfect as I could store the Member object references and their positions as Object-Key pairs, (taking care of both order and vacancies) but apparently CoreData does not support NSDictionary. Has anyone had a similar need, and devised a simple solution?

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• Looking for a generic handler/service for mongodb and asp.net / c#

  - by JohnAgan

  I am new to MongoDB and have a perfect place in mind to use it. However, it's only worth it if I can make the queries from JavaScript and return JSON. I read another post on here of someone asking a similar question, but not specific to C#. What's the easiest way I can implement a generic service/handler in asp.net/c# that would allow me to interact with mongodb via JavaScript? I understand JavaScript can't call mongodb directly, so the next best thing is what I'm looking for.

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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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• Get a list of documents from Mongo DB

  - by Andrei Neagu

  Hello, I want to do something like this: List<int> fff = new List<int>(); fff.Add(1); fff.Add(2); fff.Add(5); Mongo m = new Mongo(); m.Connect(); var dataBase = m.GetDatabase("database"); var collection = dataBase.GetCollection("coll"); IMongoQuery queryable = collection.AsQueryable(); MongoQueryProvider prov = new MongoQueryProvider(collection); var query = new MongoQuery(prov); var ffppp = from p221 in query where fff.Contains((int)p221["oid"]) select p221; This throws this error : The method 'Contains' could not be converted into a constant. I saw that mongo has an operator $in. Does any one know how can I use it from c#? (http://www.mongodb.org/display/DOCS/Advanced+Queries) Thanks

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• [PHP] building html tables from query data... faster?

  - by Andrew Heath

  With my limited experience/knowledge I am using the following structure to generate HTML tables on the fly from MySQL queries: $c = 0; $t = count($results); $table = '<table>'; while ($c < $t) { $table .= "<tr><td>$results[0]</td><td>$results[1]</td> (etc etc) </tr>"; ++$c; } $table .= '</table>'; this works, obviously. But for tables with 300+ rows there is a noticeable delay in pageload while the script builds the table. Currently the maximum results list is only about 1,100 rows, and the wait isn't long, but there's clearly a wait. Are there other methods for outputting an HTML table that are faster than my WHILE loop? (PHP only please...)

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• Only the last run in a for loop in Javascript works

  - by Mengfei Murphy

  Here is a for loop written by Javascript. It is trying to apply queries for websql. for (var i = 0; i < 10; i++){ db.transaction(function (tx){ tx.executeSql('INSERT INTO ProjSetsT (ProjID) VALUES (?);', [i]); }); } The attempt is obvious, I tried to add values "0, 1, 2, ... 9" into column ProjID in table ProjSetsT. It does not work. I only got the last element, i.e. "9" inserted, but not the first eight numbers. Is there any syntax mistakes?

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• Seeking a GUI auto-format feature for T-SQL

  - by dvanaria

  Is there a freely available GUI tool that will allow interaction with Microsoft SQL Server (via T-SQL) that provides an auto-format feature? I constantly find myself writing queries in SQL Query Analyzer (Microsoft’s standard GUI tool for T-SQL) and cutting/pasting the whole thing into SQLyog (a GUI tool for MySQL), where I can press F12 and have it reformatted into an easily readable, industry standard format. I then cut/paste this back into Query Analyzer to execute. I do this all the time at work and haven’t been able to find an alternative. I realize that SQLyog is no longer free software, but what I’m looking for is a specific alternative to a MS SQL Server interface (with auto-formatting). Thanks in advance for your help.

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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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• 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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• MySQL: Count two things in one query?

  - by Nebs

  I have a "boolean" column in one of my tables (value is either 0 or 1). I need to get two counts: The number of rows that have the boolean set to 0 and the number of rows that have it set to 1. Currently I have two queries: One to count the 1's and the other to count the 0's. Is MySQL traversing the entire table when counting rows with a WHERE condition? I'm wondering if there's a single query that would allow two counters based on different conditions? Or is there a way to get the total count along side the WHERE conditioned count? This would be enough as I'd only have to subtract one count from the other (due to the boolean nature of the column). There are no NULL values. Thanks.

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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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