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  • Linq2Sql: query - subquery optimisation

    - by Budda
    I have the following query: IList<InfrStadium> stadiums = (from sector in DbContext.sectors where sector.Type=typeValue select new InfrStadium(sector.TeamId) ).ToList(); and InfrStadium class constructor: private InfrStadium(int teamId) { IList<Sector> teamSectors = (from sector in DbContext.sectors where sector.TeamId==teamId select sector) .ToList<>(); ... work with data } Current implementation perform 1+n queries, where n - number of records fetched the 1st time. I want to optimize that. And another one I would love to do using 'group' operator in way like this: IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IEnumerable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } But attempt to launch query causes the following error: Expression of type 'System.Int32' cannot be used for constructor parameter of type 'System.Collections.Generic.IEnumerable`1[InfrStadiumSector]' Question 1: Could you please explain, what is wrong here, I don't understand why 'team_sectors' is applied as 'System.Int32'? I've tried to change query a little (replace IEnumerable with IQueryeable): IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors.AsQueryable()) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IQueryeable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } In this case I've received another but similar error: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable1[InfrStadiumSector]' of method 'System.Linq.IQueryable1[InfrStadiumSector] AsQueryableInfrStadiumSector' Question 2: Actually, the same question: can't understand at all what is going on here... P.S. I have another to optimize query idea (describe here: Linq2Sql: query optimisation) but I would love to find a solution with 1 request to DB).

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  • Error in computed Field of select Query

    - by Shehzad Bilal
    This Query is giving me an error of #1054 - Unknown column 'totalamount' in 'where clause' SELECT (amount1 + amount2) as totalamount FROM `Donation` WHERE totalamount > 1000 I know i can resolve this error by using group by clause and replace my where condition with having clause. But is there any other solution beside using having clause. If group by is the only solution then I want to know why I have to use group by clause even I havent use any aggregate function thanks.

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  • Update a list of things without hitting every entry

    - by bobobobo
    I have a list in a database that the user should be able to order. itemname| order value (int) --------+--------------------- salad | 1 mango | 2 orange | 3 apples | 4 On load from the database, I simply order by order_value. By drag 'n drop, he should be able to move apples so that it appears at the top of the list.. itemname| order value (int) --------+--------------------- apples | 4 salad | 1 mango | 2 orange | 3 Ok. So now internally I have to update EVERY LIST ITEM! If the list has 20 or 100 items, that's a lot of updates for a simple drag operation. itemname| order value (int) --------+--------------------- apples | 1 salad | 2 mango | 3 orange | 4 I'd rather do it with only one update. One way I thought of is if "internal Order" is a double value. itemname| order value (double) --------+--------------------- salad | 1.0 mango | 2.0 orange | 3.0 apples | 4.0 SO after the drag n' drop operation, I assign apples has a value that is less than the item it is to appear in front of: itemname| order value (double) --------+--------------------- apples | 0.5 salad | 1.0 mango | 2.0 orange | 3.0 .. and if an item is dragged into the middle somewhere, its order_value is bigger than the one it appears after .. here I moved orange to be between salad and mango: itemname| order value (double) --------+--------------------- apples | 0.5 salad | 1.0 orange | 1.5 mango | 2.0 Any thoughts on better ways to do this?

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  • mysqli_stmt_bind_param SQL Injection

    - by profitphp
    Is there still an injection risk when using prepared statements and mysqli_stmt_bind_param? For example: $malicious_input = 'bob"; drop table users'; mysqli_stmt_bind_param($stmt, 's', $malicious_input); Behind the scenes does mysqli_stmt_bind_param pass this query string to mysql: SET @username = "bob"; drop table users"; Or does it perform the SET command through the API, or use some type of protection to keep this from happening?

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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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  • SQLite - ON DUPLICATE KEY UPDATE

    - by Alix Axel
    MySQL has something like this: INSERT INTO visits (ip, hits) VALUES ('127.0.0.1', 1) ON DUPLICATE KEY UPDATE hits = hits + 1; As far as I'm know this feature doesn't exist in SQLite, what I want to know is if there is any way to archive the same effect without having to execute two queries. Also, if this is not possible, what do you prefer: SELECT + (INSERT or UPDATE) or UPDATE (+ INSERT if UPDATE fails)

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  • Copying 6000 tables and data from sqlserver to oracle ==> fastest method?

    - by nazer555
    i need to copy the tables and data (about 5 yrs data, 6200 tables) stored in sqlserver, i am using datastage and odbc connection to connect and datstage automatically creates the table with data, but its taking 2-3 hours per table as tables are very large(0.5 gig, 300+columns and about 400k rows). How can i achieve this the fastes as at this rate i am able to only copy 5 tables per day but within 30 days i need move over these 6000 tables.

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  • ASP Function that returns result from stored procedures

    - by Brad
    I am working on a project that requires me to hop into to separate DB's. So I have figured that I need to have multiple functions inside of my VB page. The only problem I am having,is I am not to sure how to get this all accomplished. So far I have figured out the overall structure, just need help implementing that structure. Here is my idea: The main Function would call two other functions. We can Call them Sub Function 1 and Sub Function 2. So, the main Function takes the saved sessions information for the E-mail address and dumps in into Sub Function 1. It needs to open up a new connection to the db/stored procedure and RUN the following procedure and then return the result. Here is the stored procedure and what i think is correct. CREATE PROCEDURE WEB_User ( @EMAIL_ADDRESS varchar(80) = [EMAIL_ADDRESS] ) AS SELECT MEMBER_NUMBER FROM WEB_LOGIN WHERE EMAIL_ADDRESS = @EMAIL_ADDRESS So my question is, what is the function suppose to look like? how do I send the session information to the procedure? and finally, how do I return the stored procedure results and push back into the main function so it can be carried into sub function 2? Thank you in advance for your help... I really appreciate it!

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  • MySQL Count If using 4 tables or Perl

    - by user1726133
    Hi I have a relatively convoluted query that relies on 4 different tables, unfortunately I do not have control of this data, but I do have to query it. I ran this simpler query and it works using just table 1 and table 2 SELECT actor, receiver, count(IF(t2.group1 = "anxiety behavior", 1,0)) AS 'anxiety' FROM ethogram_edited_obs_behaviors t1 JOIN ethogram_behaviors t2 on t1.behavior = t2.behavior_code GROUP BY actor; Below are the 4 tables I need and the query I tried that didn't work Table 1 | Table 2 | Table 3 | Table 4 Actor | Behavior | Behavior | type of Behavior | subject | sex | subject |subject_code er frown | frown anxiety behavior | Eric M | Eric | er Here is the query that is failing SELECT actor, count(IF(t2.group1 = "anxiety behavior", 1,0) AND(t3.sex = "M", 1,0)) AS 'anxiety', FROM ethogram_edited_obs_behaviors t1 JOIN ethogram_behaviors t2 on t1.behavior = t2.behavior_code JOIN subject_code t3 on t1.actor = t3.behavior_code1 JOIN subjects t4 on t3.subject = t4.yerkes_code GROUP BY actor; Any help would be much appreciated!! Thanks :) P.S. if this is easier to do in Perl tips also much appreciated

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  • Oracle (Old?) Joins

    - by Grasper
    I have been porting oracle selects, and I have been running across a lot of queries like so: SELECT e.last_name, d.department_name FROM employees e, departments d WHERE e.department_id(+) = d.department_id; ...and: SELECT last_name, d.department_id FROM employees e, departments d WHERE e.department_id = d.department_id(+); Are there any guides/tutorials for converting all of the variants of the (+) syntax? What is that syntax even called (so I can scour google)? When was this standard phased out? Any info is appreciated.

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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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  • mysql count rows and grop them by month

    - by user2661296
    I have a table called cc_calls and there I have many call records I want to count them and group them in months I have a timestamp called starttime and I can use that row to extract the month, also limit the count for 12 months the results should be like: Month Count January 768768 February 876786 March 987979 April 765765 May 898797 June 876876 July 786575 August 765765 September 689787 October 765879 November 897989 December 876876 Can anyone guide me or show me the mysql query that I need to get this result.

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  • Select a row having a column with max value - On a date range

    - by Abhi
    Excuse me for posting a similar question. Please consider this: date value 18/5/2010, 1 pm 40 18/5/2010, 2 pm 20 18/5/2010, 3 pm 60 18/5/2010, 4 pm 30 18/5/2010, 5 pm 60 18/5/2010, 6 pm 25 19/5/2010, 6 pm 300 19/5/2010, 6 pm 450 19/5/2010, 6 pm 375 20/5/2010, 6 pm 250 20/5/2010, 6 pm 310 The query is to get the date and value for each day such that the value obtained for that day is max. If the max value is repeated on that day, the lowest time stamp is selected. The result should be like: 18/5/2010, 3 pm 60 19/5/2010, 6 pm 450 20/5/2010, 6 pm 310 The query should take in a date range like the one given below and find results for that range in the above fashion: where date = to_date('26/03/2010','DD/MM/YYYY') AND date < to_date('27/03/2010','DD/MM/YYYY')

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  • triggers for generating userID based on user's information.

    - by nectar
    I have complaint table 1. tblProfile with columns userId | name | age | address | mobileno | 2. tblUserId with columns userId | role | status now when user fills the form I want to insert one row in tblProfile, before inserting a new row I want to create userId by combining starting letters of name and mobile no and then insert into tblprofile with userId after this I want to insert that UserId into tblUserId table. for this I have to use two triggers one is before insert trigger and another is after insert trigger.but I dont know how to capture user information to create userId and how to pass that Id to second trigger.

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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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  • C# - Rollback SqlTransaction in catch block - Problem with object accessability

    - by Marks
    Hi there. I've got a problem, and all articles or examples i found seem to not care about it. I want to do some database actions in a transaction. What i want to do is very similar to most examples: using (SqlConnection Conn = new SqlConnection(_ConnectionString)) { try { Conn.Open(); SqlTransaction Trans = Conn.BeginTransaction(); using (SqlCommand Com = new SqlCommand(ComText, Conn)) { /* DB work */ } } catch (Exception Ex) { Trans.Rollback(); return -1; } } But the problem is, that the SqlTransaction Trans is declared inside the try block. So it is not accessable in the catch() block. Most examples just do Conn.Open() and Conn.BeginTransaction() before the try block. But i think thats a bit risky, since both can throw multiple exceptions. Am I wrong, or do most people just ignore this risk? Whats the best solution to be able to rollback, if an exception happens. Thanks in advance, Marks

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  • Oracle query to select rows with unique code

    - by Jasim
    I have a table like this C1 C2 C3 Code 1 2 3 33 1 2 3 34 2 4 1 14 1 2 3 14 i want to select only those record whose code is appearing only in single row. ie, in this case rows with code 33 and 34.. as they appear only once in this table. How can i write a query for that

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  • MySQL Delete from 1 table, using multiple tables

    - by nute
    I would like to delete all the rows found by that query: SELECT cart_abandon.* FROM cart_abandon, cart_product, txn_product, users WHERE cart_abandon.cartid = cart_product.cartid AND cart_product.productid = txn_product.productid AND txn_product.username = users.username AND users.id = cart_abandon.userid AND txn_product.txndate >= cart_abandon.abandondate The thing to keep in mind is that the query here uses 4 different tables, however I only want to delete rows from 1 table (cart_abandon). Is there an easy way to do that? Maybe this: ? DELETE cart_abandon FROM cart_abandon, cart_product, txn_product, users WHERE cart_abandon.cartid = cart_product.cartid AND cart_product.productid = txn_product.productid AND txn_product.username = users.username AND users.id = cart_abandon.userid AND txn_product.txndate >= cart_abandon.abandondate Is that valid? Correct?

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