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• Need to debug LINQ simple queries in Visual Studio 2010

  - by maxima120

  I often get in a position when I need to know why my LINQ doesnt work as intended... I use object collections and extensions. I dont want spend more than couple of minutes on it. LINQ supposed to make developer's life easier not harder. I hoped VS 2010 will have it fixed but I now use RC and it still doesnt let me type LINQ and check what is going on... Says as before "Expression cannot contain lambda expressions"... Is there some add-on for Visual Studio so I can quickly and effectively run ad-hoc queries and find out what is going on and where I am wrong?

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• Making complex queries through SQLiteDatabase

  - by Luca

  Hi! I'm using the Android MediaProvider application to get information regarding the resources registered in the media library. The only way I found to do this is to use the ContentProvider class provided by the MediaProvider application. Unfortunately, it seems to me this is quite a limitation, isn't it? Is it possible this way to create complex queries with subqueries and using other functions of SQLite? I thought that it may be possible using the SQLiteDatabase class, but it seems it is not possible to open the database directly with its path, and anyway, the query method seems not to allow subqueries. Any solution to this? Thanks!

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• Compiled Queries and "Parameters cannot be sequences"

  - by David B

  I thought that compiled queries would perform the same query translation as DataContext. Yet I'm getting a run-time error when I try to use a query with a .Contains method call. Where have I gone wrong? //private member which holds a compiled query. Func<DataAccess.DataClasses1DataContext, List<int>, List<DataAccess.TestRecord>> compiledFiftyRecordQuery = System.Data.Linq.CompiledQuery.Compile <DataAccess.DataClasses1DataContext, List<int>, List<DataAccess.TestRecord>> ((dc, ids) => dc.TestRecords.Where(tr => ids.Contains(tr.ID)).ToList()); //this method calls the compiled query. public void FiftyRecordCompiledQueryByID() { List<int> IDs = GetRandomInts(50); //System.NotSupportedException //{"Parameters cannot be sequences."} List<DataAccess.TestRecord> results = compiledFiftyRecordQuery (myContext, IDs); }

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• Linq To Sql: Compiled Queries and Extension Methods

  - by Beni

  Hi community, I'm interessted, how does Linq2Sql handles a compiled query, that returns IQueryable. If I call an extension method based on a compiled query like "GetEntitiesCompiled().Count()" or "GetEntitiesCompiled().Take(x)". What does Linq2Sql do in the background? This would be very bad, so in this situation I should write a compiled query like "CountEntitiesCompiled". Does he load the result (in this case "GetEntitiesCompiled()") into the memory (mapped to the entity class like "ToList()")? So what situations make sense, when the compiled queries return IQueryable, that query is not able to modify, before request to the Sql-Server. So in my opinion I can just as good return List. Thanks for answers!

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• Is there a standard for storing normalized phone numbers in a database?

  - by Eric Z Beard

  What is a good data structure for storing phone numbers in database fields? I'm looking for something that is flexible enough to handle international numbers, and also something that allows the various parts of the number to be queried efficiently. [Edit] Just to clarify the use case here: I currently store numbers in a single varchar field, and I leave them just as the customer entered them. Then, when the number is needed by code, I normalize it. The problem is that if I want to query a few million rows to find matching phone numbers, it involves a function, like where dbo.f_normalizenum(num1) = dbo.f_normalizenum(num2) which is terribly inefficient. Also queries that are looking for things like the area code become extremely tricky when it's just a single varchar field. [Edit] People have made lots of good suggestions here, thanks! As an update, here is what I'm doing now: I still store numbers exactly as they were entered, in a varchar field, but instead of normalizing things at query time, I have a trigger that does all that work as records are inserted or updated. So I have ints or bigints for any parts that I need to query, and those fields are indexed to make queries run faster.

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• How to implement dynamic queries for MNesia?

  - by Kerem

  I'm trying to implement a function that generates dynamic queries for MNesia. For example, when function is called with these arguments; dyn_query(list, person, [name, age], ["jack", 21]) I want to query MNesia to list items whose name is "jack" and age is 21 in person table. I've tried to implement this by using qlc:q(ListComprehension) and qlc:string_to_handle("ListComprehension"). First failed because of compile errors, compiler didn't let me to use functions instead of ListComprehentions and variables instead of record names like "Item#Table.Member". Second failed, because erl_eval couldn't handle records and throwed exceptions like {undefined_record, person}. Which method should I use? How could i solve these problems? Or should I use a different method? Thanks.

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• web2py error while using distinct in the queries

  - by Steve

  Hi, I am using web2py with GAE. While using some of the queries which has a distinct clause, GAE throws out an error.I have pasted the Traceback. Can someone please help me out with this. In FILE: /base/data/home/apps/panneersoda/1.341206242889687944/applications/init/controllers/default.py Traceback (most recent call last): File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/restricted.py", line 173, in restricted exec ccode in environment File "/base/data/home/apps/panneersoda/1.341206242889687944/applications/init/controllers/default.py:profileview", line 263, in <module> File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/globals.py", line 96, in <lambda> self._caller = lambda f: f() File "/base/data/home/apps/panneersoda/1.341206242889687944/applications/init/controllers/default.py:profileview", line 97, in profileview File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/contrib/gql.py", line 675, in select (items, tablename, fields) = self._select(*fields, **attributes) File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/contrib/gql.py", line 624, in _select raise SyntaxError, 'invalid select attribute: %s' % key SyntaxError: invalid select attribute: distinct Thanks

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• Minimizing SQL queries using join with one-to-many relationship

  - by Brian

  So let me preface this by saying that I'm not an SQL wizard by any means. What I want to do is simple as a concept, but has presented me with a small challenge when trying to minimize the amount of database queries I'm performing. Let's say I have a table of departments. Within each department is a list of employees. What is the most efficient way of listing all the departments and which employees are in each department. So for example if I have a department table with: id name 1 sales 2 marketing And a people table with: id department_id name 1 1 Tom 2 1 Bill 3 2 Jessica 4 1 Rachel 5 2 John What is the best way list all departments and all employees for each department like so: Sales Tom Bill Rachel Marketing Jessica John Pretend both tables are actually massive. (I want to avoid getting a list of departments, and then looping through the result and doing an individual query for each department). Think similarly of selecting the statuses/comments in a Facebook-like system, when statuses and comments are stored in separate tables.

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• NHibernate Linq queries not returning data saved in the same transaction

  - by Andrew

  Hi, I have a situation where I am using NHibernate in a WCF service and using a TransactionScope for the transaction management. NHibernate enlists in the ambient transaction fine, but, any changes I make and save inside the transaction, are not visible to any queries I make while still in that transaction. So if I add an entity and session.save() it, then further on in the code, there is a linq query against that entities table, the entity I just added is not returned. Strangely this seems to work fine if I use explicit NHibernate transactions in my tests. Anyone have any ideas as to why and what I can do about it? Many thanks Andrew

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• C# failing LDAP queries

  - by jpkomick

  I'm trying to access an LDAP directory via the SearchRequest object in C#. I can make the same calls via an LDAP library running in and iPhone app, as well as directly via a terminal session. However, the C# queries all seem to fail. var search = new SearchRequest("ou=calendar,dc=ualberta,dc=ca", "term=*,course=094398,class=*", System.DirectoryServices.Protocols.SearchScope.Subtree, attributeLst); This returns a list of terms for the course calendar. However, making the following calls won't return results for specific courses var search = new SearchRequest("ou=calendar,dc=ualberta,dc=ca", "term=1330,course=094398", System.DirectoryServices.Protocols.SearchScope.Subtree, attributeLst); The attributeLst object has proper attribute names included, but the query always returns with zero results. Any suggestions anyone has would be greatly appreciated. Thanks.

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• MySQL slow queries

  - by jack

  The MySQL slow query log often shows a bunch of following entries in sequence. SET timestamp=1268999330; commit; # User@Host: username[username] @ localhost [] # Query_time: 4.172700 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0 SET timestamp=1268999330; commit; # User@Host: username[username] @ localhost [] # Query_time: 3.628924 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0 SET timestamp=1268999330; commit; # User@Host: username[username] @ localhost [] # Query_time: 3.116018 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0 ... Usually 6-7 "commit" queries in sequence. Anyone what they are and what's the preceding query of each of them? Thanks in advance.

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• how to combine these queries

  - by mmcgrail

  and get meaningful results. Currently I am running these three queries: SELECT t.type,t.id,s.title FROM db1.tags t INNER JOIN db1.st s ON s.id=t.id WHERE id LIKE '%%' AND t.tag='foo' AND t.type='s' ORDER BY tag desc LIMIT 0, 19 SELECT t.type,t.id,v.title FROM db1.tags t INNER JOIN db1.vi v ON v.id=t.id WHERE id LIKE '%%' AND t.tag='foo' AND t.type='v' ORDER BY tag desc LIMIT 0, 19 SELECT t.type,t.id,i.ca AS title FROM db1.tags t INNER JOIN db2.tablename i ON i.id=t.id WHERE id LIKE '%%' AND t.tag='foo' AND t.type='i' ORDER BY tag desc LIMIT 0, 19 then trying to combine the data results but what I would really prefer is if I could combine them into a single query. Any thoughts?

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• Where to put conditionals in ANSI-syntax SQL queries

  - by RenderIn

  What's the difference between these two queries? I've been resistant to jumping on the ANSI-syntax bandwagon because I have not been able to unravel various syntactical ambiguities. Is 1) returning the product of the join and only then filtering out those joined records which have weight = 500? And is 2) filtering out those prior to the join? Is 2 bad syntax? Why might I use that? 1: SELECT SOMETHING FROM FOO INNER JOIN BAR ON FOO.NAME = BAR.NAME WHERE BAR.WEIGHT < 500 2: SELECT SOMETHING FROM FOO INNER JOIN BAR ON FOO.NAME = BAR.NAME AND BAR.WEIGHT < 500

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• Combining 2 Linq queries into 1

  - by Mike Fielden

  Given the following information, how can I combine these 2 linq queries into 1. Having a bit of trouble with the join statement. 'projectDetails' is just a list of ProjectDetails ProjectDetails (1 to many) PCardAuthorizations ProjectDetails (1 to many) ExpenditureDetails Notice I am grouping by the same information and selecting the same type of information var pCardAccount = from c in PCardAuthorizations where projectDetails.Contains(c.ProjectDetail) && c.RequestStatusId == 2 group c by new { c.ProjectDetail, c.ProgramFund } into g select new { Key = g.Key, Sum = g.Sum(x => x.Amount) }; var expenditures = from d in ExpenditureDetails where projectDetails.Contains(d.ProjectDetails) && d.Expenditures.ExpenditureTypeEnum == 0 group d by new { d.ProjectDetails, d.ProgramFunds } into g select new { Key = g.Key, Sum = g.Sum(y => y.ExpenditureAmounts.FirstOrDefault(a => a.IsCurrent && !a.RequiresAudit).CommittedMonthlyRecords.ProjectedEac) };

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• Advanced queries in HBase

  - by Teflon Ted

  Given the following HBase schema scenario (from the official FAQ)... How would you design an Hbase table for many-to-many association between two entities, for example Student and Course? I would define two tables: Student: student id student data (name, address, ...) courses (use course ids as column qualifiers here) Course: course id course data (name, syllabus, ...) students (use student ids as column qualifiers here) This schema gives you fast access to the queries, show all classes for a student (student table, courses family), or all students for a class (courses table, students family). How would you satisfy the request: "Give me all the students that share at least two courses in common"? Can you build a "query" in HBase that will return that set, or do you have to retrieve all the pertinent data and crunch it yourself in code?

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• Django complex queries

  - by Josh K

  I need to craft a filter for an object that checks date ranges. Right now I'm performing a very inefficient loop which checks all the objects. I would like to simplify this to a database call. The logic is you have a start and an end date objects. I need to check if the start OR the end is within the range of an appointment. if (start >= appointment.start && start < appointment.end) || (end > appointment.start && end <= appointment.end) I could do this in SQL, but I'm not as familiar with the Django model structure for more complex queries.

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• Nesting queries in SQL

  - by ZAX

  The goal of my query is to return the country name and its head of state if it's headofstate has a name starting with A, and the capital of the country has greater than 100,000 people utilizing a nested query. Here is my query: SELECT country.name as country, (SELECT country.headofstate from country where country.headofstate like 'A%') from country, city where city.population > 100000; I've tried reversing it, placing it in the where clause etc. I don't get nested queries. I'm just getting errors back, like subquery returns more than one row and such. If someone could help me out with how to order it, and explain why it needs to be a certain way, that'd be great.

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• problem in decreasing page's queries

  - by Mac Taylor

  hey guys i have a tag table in my php/mysql project that looks like this Table name : bt_tags Table fileds : tid,tag and for every story rows there is a filed named : tags Table name: stories table filed : tags that saved in this field as ids 1 5 6 space between them now problem : when using while loop to fetch all fields in story table , the page uses 1 query to show every stories' detail but for showing tag's names , i should query another table to find names , we have ids stored in story table now i used for loop between while loop to show tag names but im sure there is a better way to decrease page queries how can i improve this script and show tag's names without using *for loop ?* $result = $db->sql_query("SELECT * FROM ".STORY_TABLE." "); while ($row = $db->sql_fetchrow($result)) { //fetching other $vars ---- $tags_id = explode(" ",$row['tags']); $c = count($tags_id); for($i=1;$i<$c-1;$i++){ list($tag_name,$slug) = $db->sql_fetchrow($db->sql_query( 'SELECT `tag`,`slug` FROM `bt_tags` WHERE `tid` = "'.tags_id[$i].'" LIMIT 1' )); $sow_tags = '$tag_name,'; }

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• Caching result of SELECT statement for reuse in multiple queries

  - by Andrew

  I have a reasonably complex query to extract the Id field of the results I am interested in based on parameters entered by the user. After extracting the relevant Ids I am using the resulting set of Ids several times, in separate queries, to extract the actual output record sets I want (by joining to other tables, using aggregate functions, etc). I would like to avoid running the initial query separately for every set of results I want to return. I imagine my situation is a common pattern so I am interested in what the best approach is. The database is in MS SQL Server and I am using .NET 3.5.

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• Results from two queries at once in sqlite?

  - by SF.

  I'm currently trying to optimize the sluggish process of retrieving a page of log entries from the SQLite database. I noticed I almost always retrieve next entries along with count of available entries: SELECT time, level, type, text FROM Logs WHERE level IN (%s) ORDER BY time DESC, id DESC LIMIT LOG_REQ_LINES OFFSET %d* LOG_REQ_LINES ; together with total count of records that can match current query: SELECT count(*) FROM Logs WHERE level IN (%s); (for a display "page n of m") I wonder, if I could concatenate the two queries, and ask them both in one sqlite3_exec() simply concatenating the query string. How should my callback function look then? Can I distinguish between the different types of data by argc? What other optimizations would you suggest?

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• Similar SQL queries returning different results...

  - by Pablo

  Here are the SQL Queries: $sql1 = "SELECT count(thread) AS total FROM comments WHERE thread=1 AND parent_id=0 "; $sql2 = "SELECT count(thread) AS total FROM comments, users WHERE thread=1 AND parent_id=0 AND users.user_id=comments.user_id "; $sql3 = "SELECT comments.*, users.username AS username FROM comments, users WHERE thread=1 AND parent_id=0 AND users.user_id=comments.user_id ORDER BY date LIMIT 10, 5 "; My question is why would $sql1 and $sql2 would return two different results? $sql1 returns 61 rows $sql2 returns 56 rows The 5th line in $sql2 is just for testing, is not required, is just a variation of $sql1 which gets the total rows for a pagination.

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• Django: optimizing queries

  - by Josh

  I want to list the number of items for each list. How can I find this number in a single query, rather than a query for each list? Here is a simplified version of my current template code: {% for list in lists %} <li> {{ listname }}: {% with list.num_items as item_count %} {{ item_count }} item{{ item_count|pluralize }} {% endwith %} </li> {% endfor %} lists is passed as: List.objects.filter(user=user) and num_items is a property of the List model: def _get_num_items(self): return self.item_set.filter(archived=False).count() num_items = property(_get_num_items) This queries SELECT COUNT(*) FROM "my_app_item" WHERE... n times, where n is the number of lists. Is it possible to make a single query here?

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• AS or not to AS, queries

  - by zeMinimalist

  I'm fairly new to PHP/MySql and using queries in general. I was just wondering if there's any benefit to using "AS" in a query other than trying to make it look cleaner? Does it speed up the query at all? I probably could have figured this out by a google search but I wanted to ask my first question and see how this works. I WILL select an answer (unlike some people...) with: SELECT news.id as id news.name as name FROM news without: SELECT news.id news.name FROM news A more complex example from a many-to-many relationship tutorial I found: SELECT c.name, cf.title FROM celebrities AS c JOIN ( SELECT icf.c_id, icf.f_id, f.title FROM int_cf AS icf JOIN films AS f ON icf.f_id = f.f_id ) AS cf ON c.c_id = cf.c_id ORDER BY c.c_id ASC

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• Mongo: Finding from multiple queries

  - by waxical

  New to Mongo here. I'm using the PHP lib and trying to work out how I can find in a collection from multiple queries. I could do this by repeating the query with a different query, but I wondered if it can be done in one. I.e. $idsToLookFor = array(2124,4241,5553); $query = $db->thisCollection->find(array('id' => $idsToLookFor)); That's what I'd like to do. However it doesn't work. What I'm trying to do is find a set of results for all the id's at one time. Possible or just do a findOne on each with a foreach/for?

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• Optimizing MySQL queries with IN operator

  - by Arkadiusz Kondas

  I have a MySQL database with a fairly large table where the products are. Each of them has its own id and categoryId field where there is a category id belongs to this product. Now I have a query that pulls out products from given categories such as: SELECT * FROM products WHERE categoryId IN ( 1, 2, 3, 4, 5, 34, 6, 7, 8, 9, 10, 11, 12 ) Of course, come a WHERE clause and ORDER BY sort but not in this thing. Let's say that these products is 250k and the visits are over 100k per day. Under such conditions in the table slow_log registered weight of these queries with large generation time. Do you have any ideas how to optimize the given problem? Table engine is MyISAM.

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