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• MySQL indexes: how do they work?

  - by bob-the-destroyer

  I'm a complete newbie with MySQL indexes. I have several MyISAM tables on MySQL 5.0x having utf8 charsets and collations with 100k+ records each. The primary keys are generally integer. Many columns on each table may have duplicate values. I need to quickly count, sum, average, or otherwise perform custom calculations on any number of fields in each table or joined on any number of others. I found this page giving an overview of MySQL index usage: http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html, but I'm still not sure I'm using indexes right. Just when I think I've made the perfect index out of a collection of fields I want to calculate against, I get the "index must be under 1000 bytes" error. Can anyone explain how to most efficiently create and use indexes to speed up queries? Caveat: upgrading Mysql is not possible in this case. Using Navicat Light for db administration, but this app isn't required.

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• Doing a join across two databases with different collations on SQL Server and getting an error.

  - by Andrew G. Johnson

  I know, I know with what I wrote in the question I shouldn't be surprised. But my situation is slowly working on an inherited POS system and my predecessor apparently wasn't aware of JOINs so when I looked into one of the internal pages that loads for 60 seconds I see that it's a fairly quick, rewrite these 8 queries as one query with JOINs situation. Problem is that besides not knowing about JOINs he also seems to have had a fetish for multiple databases and surprise, surprise they use different collations. Fact of the matter is we use all "normal" latin characters that English speaking people would consider the entire alphabet and this whole thing will be out of use in a few months so a bandaid is all I need. Long story short is I need some kind of method to cast to a single collation so I can compare two fields from two databases. Exact error is: Cannot resolve the collation conflict between "SQL_Latin1_General_CP850_CI_AI" and "SQL_Latin1_General_CP1_CI_AS" in the equal to operation.

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• How to Sum calulated fields

  - by Nazero Jerry

  I‘d like to ask I question that here that I think would be easy to some people. Ok I have query that return records of two related tables. (One to many) In this query I have about 3 to 4 calculated fields that are based on the fields from the 2 tables. Now I want to have a group by clause for names and sum clause to sum the calculated fields but it ends up in error message saying: “You tried to execute a query that is not part of aggregate function” So I decided to just run the query without the totals *(ie no group by , sum etc,,,) : And then I created another query that totals my previous query. ( i.e. using group by clause for names and sum for calculated fields… no calculation here) This is fine ( I use to do this) but I don’t like having two queries just to get summary total. Is their any other way of doing this in the design view and create only one query?. I would very much appreciate. Thankyou: JM

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• Management Studio default file save location

  - by jayrdub

  Open a new query window. Write some SQL. Save the script, the Save File As dialog box opens - but always to the same default location in the Profiles directory. Is there any way to set my default file location? ...Like I used to do with apps from the 1980s? Under Tools|Options a default location can be specified for query results. I need the same thing for new queries (the text editor). Tried changing locations in the Registry but SSMS just overwrote my changes. Any suggestions? (I saw this unanswered question at http://www.eggheadcafe.com/software/aspnet/30098335/management-studio-default.aspx and I had same exact question so I just reposted it here)

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• Instrumenting Database Access

  - by Whisk

  Jeff mentioned in one of the podcasts that one of the things he always does is put in instrumentation for database calls, so that he can tell what queries are causing slowness etc. This is something I've measured in the past using SQL Profiler, but I'm interested in what strategies other people have used to include this as part of the application. Is it simply a case of including a timer across each database call and logging the result, or is there a 'neater' way of doing it? Maybe there's a framework that does this for you already, or is there a flag I could enable in e.g. Linq-to-SQL that would provide similar functionality. I mainly use c# but would also be interested in seeing methods from different languages, and I'd be more interested in a 'code' way of doing this over a db platform method like SQL Profiler.

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• count(*) is it really expensive ?

  - by Anil Namde

  I have a page where i have 4 tabs displaying 4 different reports based of different tables. Now i get row count of each tabled using select count() from table query and display number of rows available in each table on the tabs. Now with each page post back 5 count() queries are executed (4 to get counts and 1 for pagination) and 1 query for getting report. Now my question is should is count(*) query really expensive that i should keep the row counts (at least which are displayed on tab) in view state of page instead of queering each time? How much expensive it is ?

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• XSD generation from a MS SQL database using schemas

  - by madprog

  I'm willing to use NDbUnit on a MS SQL database which uses schemas. I have to generate the XSD schema from the database. Visual Studio has a tool to do that, but Visual Studio 2005 doesn't include the schema information in the generated XSD. Therefore, NDbUnit fails because the generated SQL queries do not match the database. Worse, when I try to use Proteus, the XSD schema doesn't validate against the database, and Proteus fails with a warning telling that data could be lost if this check was skipped. So, my question is: is there any tool that would generate my XSD schema properly and from the database information?

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• 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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• Compare range of ip addresses with start and end ip address in MySQL

  - by Maarten

  I have a MySQL table where I store IP ranges. It is setup in the way that I have the start address stored as a long, and the end address (and an id and some other data). Now I have users adding ranges by inputting a start and end ip address, and I would like to check if the new range is not already (partially) in the database. I know I can do a between query, but that doesn't seem to work with 2 different columns, and I also cannot figure out how to pass a range to compare it. Doing it in a loop in PHP is a possibility, but would with a range of e.g. 132.0.0.0-199.0.0.0 be quite a big amount of queries..

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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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• How do you verify the correct data is in a data mart?

  - by blockcipher

  I'm working on a data warehouse and I'm trying to figure out how to best verify that data from our data cleansing (normalized) database makes it into our data marts correctly. I've done some searches, but the results so far talk more about ensuring things like constraints are in place and that you need to do data validation during the ETL process (E.g. dates are valid, etc.). The dimensions were pretty easy as I could easily either leverage the primary key or write a very simple and verifiable query to get the data. The fact tables are more complex. Any thoughts? We're trying to make this very easy for a subject matter export to run a couple queries, see some data from both the data cleansing database and the data marts, and visually compare the two to ensure they are correct.

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• Which SQL query is faster? Filter on Join criteria or Where clause?

  - by Jon Erickson

  Compare these 2 queries. Is it faster to put the filter on the join criteria or in the were clause. I have always felt that it is faster on the join criteria because it reduces the result set at the soonest possible moment, but I don't know for sure. I'm going to build some tests to see, but I also wanted to get opinions on which would is clearer to read as well. Query 1 SELECT * FROM TableA a INNER JOIN TableXRef x ON a.ID = x.TableAID INNER JOIN TableB b ON x.TableBID = b.ID WHERE a.ID = 1 /* <-- Filter here? */ Query 2 SELECT * FROM TableA a INNER JOIN TableXRef x ON a.ID = x.TableAID AND a.ID = 1 /* <-- Or filter here? */ INNER JOIN TableB b ON x.TableBID = b.ID

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• SQL Server 2008 - Search Query

  - by user208662

  Hello, I am not a SQL Expert. I’m trying to elegantly solve a query problem that others have had to have had. Surprisingly, Google is not returning anything that is helping. Basically, my application has a “search” box. This search field will allow a user to search for customers in the system. I have a table called “Customer” in my SQL Server 2008 database. This table is defined as follows: Customer UserName (nvarchar) FirstName (nvarchar) LastName (nvarchar) As you can imagine, my users will enter queries of varying cases and probably mis-spell the customer’s names regularly. How do I query my customer table and return the 25 results that are closest to their query? I have no idea how to do this ranking and consider the three fields listed in my table. Thank you!

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• how do i use MySql ENUM type? (and is it right for a news feed)

  - by Haroldo

  I'm creating a table called news_feed, this will log all the actions a user performs. Lets say I want to store user1234 deleted article412 at midday I then need a table like so timestamp | user_id | subject_type | subject_id | method . there would be 5 potential methods to log, methods = add/edit/delete/update/report and lets say 2 possible subject_type subjects = article/comment I know i could make my own key where 0=add, 1=delete etc etc but this would make my queries cumbersome to use/write as i'd need to keep consulting the key. Is there a MySql type which can read lots of identially values quickly? is this ENUM? how do i use it?!!

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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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• Whats the proper way of accessing a database through an assembly?

  - by H4mm3rHead

  Hi, I have a ASP.NET MVC application which is build up as an assembly that queries the database and a asp.net frontend that references this assembly and this assembly abstracts the underlying database. This means that my Assembly contains a app.config file that contains the connectionstring to the database (Linq to Sql data model). How do I go about making this more flexible? Should i make a "initialize()" method somewhere in my assembly which takes the connection string from the asp.net mvc application and then that controls which database to use? or how is this done?

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• Can I expect a performance gain from removing this JOIN?

  - by makeee

  I have a "items" table with 1 million rows and a "users" table with 20,000 rows. When I select from the "items" table I do a join on the "users" table (items.user_id = user.id), so that I can grab the "username" from the users table. I'm considering adding a username column to the items table and removing the join. Can I expect a decent performance increase from this? It's already quite fast, but it would be nice to decrease my load (which is pretty high). The downside is that if the user changes their username, items will still reflect their old username, but this is okay with me if I can expect a decent performance increase. I'm asking stackoverflow because benchmarks aren't telling me too much. Both queries finish very quickly. Regardless, I'm wondering if removing the join would lighten load on the database to any significant degree.

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• Need an alternative to two left joins.

  - by Scarface

  Hey guys quick question, I always use left join, but when I left join twice I always get funny results, usually duplicates. I am currently working on a query that Left Joins twice to retrieve the necessary information needed but I was wondering if it were possible to build another select statement in so then I do not need two left joins or two queries or if there were a better way. For example, if I could select the topic.creator in table.topic first AS something, then I could select that variable in users and left join table.scrusersonline. Thanks in advance for any advice. SELECT * FROM scrusersonline LEFT JOIN users ON users.id = scrusersonline.id LEFT JOIN topic ON users.username = topic.creator WHERE scrusersonline.topic_id = '$topic_id' The whole point of this query is to check if the topic.creator is online by retrieving his name from table.topic and matching his id in table.users, then checking if he is in table.scrusersonline. It produces duplicate entries unfortunately and is thus inaccurate in my mind.

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• How to efficiently handle Where and OrderBy clauses

  - by Goran

  My business layer passes all the required information to UI layer. From what I have read, in general, best practice is to send fetched data to UI layer, and to avoid passing queries like ObjectQuery. My problem with this approach is next: If I am to make a flexible business layer, then I should allow UI to sort the data anyway it requires. Fetching sorted data from database, and then resorting them in UI is kind of bad practice for me, so the only way is to somehow So what are my options? Is there a way to make it like this: public void OrderByMethod(params ...) { .... } so I can call it like this: OrderByMethod(MyEntity.Property1, MyEntity.Property2 descending....); Thanks, Goran

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• is there a tool to see the difference between two database tables in SQL Server?

  - by reinier

  What is a good tool to see the differences between 2 tables (or even better, the datasets returned by 2 queries). EDIT: I'm not interested in the schema changes. Just assume that the schemas are the same. background as to why: I'm porting some legacy code which can fill a database with some pre-calced data. The easiest way to see if I got everything right, is to check the output of the old program, with the new one. I was thinking that if there is some kind of 'diff' tool for databases, this might be great.

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• Sql query - how to construct

  - by Max Malmgren

  Hi. I am working to implement a dataconnection between my C# application and an Sql Express database. Please bear in mind I have not worked with Sql queries before. I have the following relevant tables: ArticlesCommon ArticlesLocalized CategoryCommon CategoryLocalized where ArticlesCommon holds language independent information such as price, weight etc. This is the statement for now: SELECT * FROM ArticlesCommon INNER JOIN ArticlesLocalized ON ArticlesCommon.ID = ArticlesLocalized.ID WHERE ArticlesLocalized.Language = @language ORDER BY ArticlesCommon.DateAdded ArticlesCommon contains a category id for each row. Now, I want to use this to look up the localized information in CategoryLocalized and add it to the result, something like SELECT *, CategoryLocalized.Name as CategoryName. If I have gotten my point across, is this doable? Thank you.

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• SQL Server indexed view matching of views with joins not working

  - by usr

  Does anyone have experience of when SQL Servr 2008 R2 is able to automatically match indexed view (also known as materialized views) that contain joins to a query? for example the view select dbo.Orders.Date, dbo.OrderDetails.ProductID from dbo.OrderDetails join dbo.Orders on dbo.OrderDetails.OrderID = dbo.Orders.ID cannot be automatically matched to the same exact query. When I select directly from this view ith (noexpand) I actually get a much faster query plan that does a scan on the clustered index of the indexed view. Can I get SQL Server to do this matching automatically? I have quite a few queries and views... I am on enterprise edition of SQL Server 2008 R2.

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• Active record taking Date.today as yesterday

  - by Mongus Pong

  I have a strange one.. I am doing something like : tip = find (:first, :conditions => ["last_shown = ? or last_shown is null", Date.today]) And then a little later on I do : tip.last_shown = Date.today tip.save When I look at output of these queries, ActiveRecord is doing the first query with todays date as I would expect. However, the send query, ActiveRecord is setting the last_shown date to be yesterdays date. Why on earth would it do this? I have config.time_zone = 'UTC' in my environment.rb. I can use Time.now.utc.to_date instead of Date.today but it makes no difference.

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• Expand in linq not loading inner data collections from service.

  - by Kit

  I am seeing odd behavior with service queries! I am using MVVM pattern for a silverlight 3 app on 3.5 framework and Dataservices 1.5. The following code eager loads correctly the parent object and the child heirarchy perfectly IF and ONLY IF I am preloading the data. But I would like to fetch a different set of the parent object (and its child heirarchy) on different button clicks. What I am seeing is that on button click, only the parent object is retrieved, and the child heirarchy contains nothing. Any suggestions? Any ideas how to tackle this? Thanks all. The method: DataServiceQuery serviceQuery = (DataServiceQuery)(from m1 in dbEntities.gis_Region.Expand("gis_RegionValue/gis_Measure") where m1.RegionGuid == new Guid(regionGuid) select m1); serviceQuery.BeginExecute(GetRegionDetailAsyncResult, serviceQuery); The wired Async Result: DataServiceQuery query = (DataServiceQuery)result.AsyncState; gis_Region region = query.EndExecute(result).First();

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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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