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  • Storing users in a database

    - by EMcKenna
    Im wondering whats the best way of storing different types of users in my database. I am writing an application that has 4 main user types (admin, school, teacher, student). At the moment I have a table for each of these but i'm not sure thats the best way of storing user information. For instance... Allowing students to PM other student is simple (store sender and receiver student_id) but enabling teachers to PM students requires another table (sender teacher_id, sender student_id). Should all users be stored in one users table with a user_type field? If so, the teacher / student specific information will still have to be stored in another table. users user_id, password_hash, user_type students user_id, student_specific_stuff... teachers user_id, teacher_specific_stuff... How do I stop a user who has a user_type = student from being accidentally being entered into the teachers table (as both have a user_id) Just want to make sure I get the database correct before i go any further. Thanks...

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  • Extract multiple values from one column in MySql

    - by Neil
    I've noticed that MySql has an extensive search capacity, allowing both wildcards and regular expressions. However, I'm in somewhat in a bind since I'm trying to extract multiple values from a single string in my select query. For example, if I had the text "<span>Test</span> this <span>query</span>", perhaps using regular expressions I could find and extract values "Test" or "query", but in my case, I have potentially n such strings to extract. And since I can't define n columns in my select statement, that means I'm stuck. Is there anyway I could have a list of values (ideally separated by commas) of any text contained with span tags? In other words, if I ran this query, I would get "Test,query" as the value of spanlist: select <insert logic here> as spanlist from HtmlPages ...

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  • validate linqtosql mapping to a model

    - by Coppermill
    I have generated a LinqtoSQL mapping xml file, which I have a valid XSD schema that I check to make sure the XML is correct. Now I want to check that the field type match the Model/Interface for example: checking that the nullable fields are nullable that int are int etc anyone got any ideas if I can do this?

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  • How to SELECT DISTINCT Info with TOP 1 Info and an Order By FROM the Top 1 Info

    - by Erin Taylor
    I have 2 tables, that look like: CustomerInfo(CustomterID, CustomerName) CustomerReviews(ReviewID, CustomerID, Review, Score) I want to search reviews for a string and return CustomerInfo.CustomerID and CustomerInfo.CustomerName. However, I only want to show distinct CustomerID and CustomerName along with just one of their CustomerReviews.Reviews and CustomerReviews.Score. I also want to order by the CustomerReviews.Score. I can't figure out how to do this, since a customer can leave multiple reviews, but I only want a list of customers with their highest scored review. Any ideas?

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  • Database indexes and their Big-O notation

    - by miket2e
    I'm trying to understand the performance of database indexes in terms of Big-O notation. Without knowing much about it, I would guess that: Querying on a primary key or unique index will give you a O(1) lookup time. Querying on a non-unique index will also give a O(1) time, albeit maybe the '1' is slower than for the unique index (?) Querying on a column without an index will give a O(N) lookup time (full table scan). Is this generally correct ? Will querying on a primary key ever give worse performance than O(1) ? My specific concern is for SQLite, but I'd be interested in knowing to what extent this varies between different databases too.

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  • SqlCE DB occasionally freezes on one handheld, not another

    - by Michael
    I have two types of custom handhelds which are similar, but slightly different, each running the same WinForm application and a WinCE database: Type 1: WinCE 4.2, 400 mhz, 93244 kb Type 2: WinCE 5.0, 520 mhz, 84208 kb Type 1 will happily proceed through a large batch db operation (initiated) by the app, by Type 2 will consistently begin c-r-a-w-l-i-n-g (for several to many cycles) at around the 200 cycle mark. As several points it will begin running normally and then crawl again. The app does several db op's (inserts, updates and selects, no deletes). To simplify my situation, I've built a small test app which essentially does this: command_s.CommandText = "select dvr from vr where vid = 2211250"; command_u.CommandText = "update pvr set LocationID=81 where Status='OK' and vri = 27861"; while(going) { command_s.ExecuteScalar(); command_u.ExecuteNonQuery(); } and set it off running on the two units side by side. Sure enough, the slower (400 mhz) unit is outpacing the faster (520 mhz) unit (it's about 5000 cycles ahead right now) and I can see noticable pauses on the 520 mhz unit. What is causing this?

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  • Complicated conditional SQL query

    - by DevAno1
    I'm not even sure if it's possible but I need it for my Access database. So I have following db structure : Now I need to perform a query that takes category_id from my product and do the magic : - let's say product belongs to console (category_id is in table Console) - from console_types take type_id, where category_id == category_id - but if product belongs to console_game (category_id is in table console_game) - from console_game take game_cat_id, where category_id == category_id I'm not sure if mysql is capable of such thing. If not I'm really f&%ranked up. Maybe there is a way to split this into 2,3 separate queries ?

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  • How to secure the communication between an MSSQL database and a c# administrative tool?

    - by citronas
    How can I secure the communication between a C# programm running locally on my computer and a MSSQL Server in a hosted environment? I have an asp.net application that is secured by SSL encryption. So using the asp.net from an open wlan connection is no problem. How can I achieve the same kind of encryption for my administrative tool? Would it be best to write a service? But how would that connection to the service be secured?

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  • Optimizing MySQL statement with lot of count(row) an sum(row+row2)...

    - by Zombies
    I need to use InnoDB storage engine on a table with about 1mil or so records in it at any given time. It has records being inserted to it at a very fast rate, which are then dropped within a few days, maybe a week. The ping table has about a million rows, whereas the website table only about 10,000. My statement is this: select url from website ws, ping pi where ws.idproxy = pi.idproxy and pi.entrytime > curdate() - 3 and contentping+tcpping is not null group by url having sum(contentping+tcpping)/(count(*)-count(errortype)) < 500 and count(*) > 3 and count(errortype)/count(*) < .15 order by sum(contentping+tcpping)/(count(*)-count(errortype)) asc; I added an index on entrytime, yet no dice. Can anyone throw me a bone as to what I should consider to look into for basic optimization of this query. The result set is only like 200 rows, so I'm not getting killed there.

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  • Need help with REGEXP_REPLACE

    - by Randy
    hey regex guru's I have a data column that contains a substring similar to this: 'This is a string with ID=123 contained inside' i need to replace the ID=123 with another fixed string say ID=1 i have a working REPLACE call that swaps out the values correctly, but this only works on a known original id number. I can extend to make it work when the number of digits are known by using some substr magic, however, the id number may have an arbitrary number of digits, so i'm thinking regex. any help with the regex magix to grab the entire ID=999 substring no matter how many digits would be very helpful. thanks

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  • Nested query to find details in table B for maximum value in table A

    - by jpatokal
    I've got a huge bunch of flights travelling between airports. Each airport has an ID and (x,y) coordinates. For a given list of flights, I want to find the northernmost (highest x) airport visited. Here's the query I'm currently using: SELECT name,iata,icao,apid,x,y FROM airports WHERE y=(SELECT MAX(y) FROM airports AS a , flights AS f WHERE (f.src_apid=a.apid OR f.dst_apid=a.apid) ) This works beautifully and reasonably fast as long as y is unique, but fails once it isn't. What I'd want to do instead is find the MAX(y) in the subquery, but return the unique apid for the airport with the highest y. Any suggestions?

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  • Timeout LinqToSql inserting millions of records

    - by Bas
    I'm inserting approximently 3 million records in a database using this solution. Eventually when the application has been inserting records for a while (my last run lasted around 4 hours), it gives a timeout with the following SqlException: "SqlExcepetion: Timeout expired. The timeoutperiod elapsed prior to completion of the operation or the server is not responding." What's the best way to handle this exception? Is there a way to prevent this from happening or should I catch the exception? Thanks in advance!

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  • Add LINQ Auto-Generated Value Marker [Column(IsDbGenerated=true)] in Buddy Class

    - by Alex
    Hello, is it possible to decorate a field of a LINQ generated class with [Column(IsDbGenerated=true)] using a buddy class (which is linked to the LINQ class via [MetadataType(typeof(BuddyMetadata))]) ? My goal is to be able to clear and repopulate the LINQ ORM designer without having to set the "Auto Generate Value" property manually every time to re-establish the fact that certain columns are autogenerated. Thanks!

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  • how to implement undo operation in datagridview

    - by ush
    Hi, I have created one application in c#.net.Using this application we can update datagridview,now i need to implement undo in it plz give me some ideas. private void button29_Click(object sender, EventArgs e) { Datatable dt; dt.RejectChanges(); } using above code i can do undo before updating. but i need a undo feature as in word plz suggest me thanks in advance

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  • MySQL: Count occurrences of known (or enumerated) distinct values

    - by Eilidh
    After looking at how to count the occurrences of distinct values in a field, I am wondering how to count the occurrences of each distinct value if the distinct values are known (or enumerated). For example, if I have a simple table - TrafficLight Colour ------------ ------ 1 Red 2 Amber 3 Red 4 Red 5 Green 6 Green where one column (in this case Colour) has known (or enumerated) distinct values, how could I return the count for each colour as a separate value, rather than as an array, as in the linked example. To return an array with a count of each colour (using the same method as in the linked example), the query would be something like SELECT Colour COUNT(*) AS ColourCount FROM TrafficLights GROUP BY Colour, and return an array - Colour ColourCount ------ ----------- Red 3 Amber 1 Green 2 What I would like to do is to return the count for each Colour AS a separate total (e.g. RedCount). How can I do this?

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  • select from varchar2 column with numeric value sometimes gives invalid number error

    - by Rene
    I'm trying to understand why, on some systems, I get an invalid number error message when I'm trying to select a value from a varchar2 column while on other systems I don't get the error while doing the exact same thing. The table is something like this: ID Column_1 Column_2 1 V text 2 D 1 3 D 2 4 D 3 and a query: select ID from table where column_1='D' and column_2 = :some_number_value :some_number_value is always numeric but can be null. We've fixed the query: select ID from table where column_1='D' and column_2 = to_char(:some_number_value) This original query runs fine on most systems but on some systems gives an "invalid number" error. The question is why? Why does it work on most systems and not on some?

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