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  • Does the order of the columns in a SELECT statement make a difference?

    - by Frank Computer
    This question was inspired by a previous question posted on SO, "Does the order of the WHERE clause make a differnece?". Would it improve a SELECT statement's performance if the the columns used in the WHERE section are placed at the begining of the SELECT statement? example: SELECT customer.id, transaction.id, transaction.efective_date, transaction.a, [...] FROM customer, transaction WHERE customer.id = transaction.id; I do know that limiting the list of columns to only the needed ones in a SELECT statement improves performance as opposed to using SELECT * because the current list is smaller.

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  • SSRS run SQL/DataSet conditionally

    - by MikeTWebb
    Hello.... I have an SSRS report that contains several subreports. The user has the ability to select/deselect which subreports they want to produce using several Boolean parameters. If a subreport is deselected then it is not rendered by setting the Visibility property. However, the DataSet associated with the de-selected subreport still executes causing the execution time to take longer than expected. Is there any way to tell a dataset on a subreport or Tablix not to execute based on a Parameter selection? Thanks

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  • is NATURAL JOIN any better than SELECT FROM WHERE in terms of performance ?

    - by ashy_32bit
    Today I got into a debate with my project manager about Cartesian products. He says a 'natural join' is somehow much better than using 'select from where' because the later cause the db engine to internally perform a Cartesian product but the former uses another approach that prevents this. As far as I know, the natural join syntax is not any different in anyway than 'select from where' in terms of performance or meaning, I mean you can use either based on your taste. SELECT * FROM table1,table2 WHERE table1.id=table2.id SELECT * FROM table1 NATURAL JOIN table2 please elaborate about the first query causing a Cartesian product but the second one being somehow more smart

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  • Problem with MySQL query

    - by Psyche
    This time my setup looks like this: one table with galleries names (gallery_id, gallery_name) and another table with galleries photos (photo_id, photo_gallery_id, photo_name). What I need is to get all the galleries with one random picture for each gallery. Is it possible to do this with a single query?

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  • comparing rows on a mysql table

    - by user311324
    Ok here's the deal I got one table with a bunch of client information. Each client makes up to one purchase a year which is represented by an individual row. there's a column for the year and there's a column the contains a unique identifier for each client. What I need to do is to construct a query that takes last year and this year and shows me which clients were here made a purchase last year but not make a purchase this year. I also need to build a query that shows me which clients did not make a purchase last year and the year before last but did make a purchase this year.

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  • Help doing a dynamic sort?

    - by Kevin
    I have a notifications table which contains different types of notifications for different events. Inside the table is a notifications_type:string column that contains the type of notification, i.e. "foo" or "bar" or "oof" I want the user to be able to select what notifications they want to display, so there are checkboxes below the result that correspond to prefs_display_foo:boolean, prefs_display_bar:boolean in the User model. What is an elegant way for me to set the :conditions in the find to properly display the sorted results? Also, currently I have it as a method in the user, but how would I do it as a has_many :notifications, :conditions = .....

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  • Facing trouble in retrieving relevant records

    - by Umaid
    SELECT * from MainCategory where Month = 'May' and Day in ((cast(strftime('%d',date('now','-1 day')) as Integer)),(cast(strftime('%d',date('now')) as Integer)),(cast(strftime('%d',date('now','+1 day')) as Integer))); Whenever I run this query in sqlite so it returns me 33 records instead of 3. I am insterested in fetching on 3 records of the current month but unable to do so, so plz assist. --Please note: if you can't assist so plz don't post irrelevant answer. I have also modified and try to make it simple but not achieve Select day, month from MainCategory where Month = 'May' and day in ((date('now','-1 day')),(date('now')),(date('now','+1 day')))

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  • Multiple column Union Query without duplicates

    - by Adam Halegua
    I'm trying to write a Union Query with multiple columns from two different talbes (duh), but for some reason the second column of the second Select statement isn't showing up in the output. I don't know if that painted the picture properly but here is my code: Select empno, job From EMP Where job = 'MANAGER' Union Select empno, empstate From EMPADDRESS Where empstate = 'NY' Order By empno The output looks like: EMPNO JOB 4600 NY 5300 MANAGER 5300 NY 7566 MANAGER 7698 MANAGER 7782 MANAGER 7782 NY 7934 NY 9873 NY Instead of 5300 and 7782 appearing twice, I thought empstate would appear next to job in the output. For all other empno's I thought the values in the fields would be (null). Am I not understanding Unions correctly, or is this how they are supposed to work? Thanks for any help in advance.

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  • Update table with index is too slow

    - by pauloya
    Hi, I was watching the Profiler on a live system of our application and I saw that there was an update instruction that we run periodically (every second) that was quite slow. It took around 400ms every time. The query includes this update (which is the slow part) UPDATE BufferTable SET LrbCount = LrbCount + 1, LrbUpdated = getdate() WHERE LrbId = @LrbId This is the table CREATE TABLE BufferTable( LrbId [bigint] IDENTITY(1,1) NOT NULL, ... LrbInserted [datetime] NOT NULL, LrbProcessed [bit] NOT NULL, LrbUpdated [datetime] NOT NULL, LrbCount [tinyint] NOT NULL, ) The table has 2 indexes (non unique and non clustered) with the fields by this order: * Index1 - (LrbProcessed, LrbCount) * Index2 - (LrbInserted, LrbCount, LrbProcessed) When I looked at this I thought that the problem would come from Index1 since LrbCount is changing a lot and it changes the order of the data in the index. But after desactivating index1 I saw the query was taking the same time as initially. Then I rebuilt index1 and desactivated index2, this time the query was very fast. It seems to me that Index2 should be faster to update, the order of the data shouldn't change since the LrbInserted time is not changed. Can someone explain why index2 is much heavier to update then index1? Thank you!

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  • Select Query Joined on Two Fields?

    - by btollett
    I've got a few tables in an access database: ID | LocationName 1 | Location1 2 | Location2 ID | LocationID | Date | NumProductsDelivered 1 | 1 | 12/10 | 3 2 | 1 | 01/11 | 2 3 | 1 | 02/11 | 2 4 | 2 | 11/10 | 1 5 | 2 | 12/10 | 1 ID | LocationID | Date | NumEmployees | EmployeeType 1 | 1 | 12/10 | 10 | 1 (=Permanent) 2 | 1 | 12/10 | 3 | 2 (=Temporary) 3 | 1 | 12/10 | 1 | 3 (=Support) 4 | 2 | 10/10 | 1 | 1 5 | 2 | 11/10 | 2 | 1 6 | 2 | 11/10 | 1 | 2 7 | 2 | 11/10 | 1 | 3 8 | 2 | 12/10 | 2 | 1 9 | 2 | 12/10 | 1 | 3 What I want to do is pass in the LocationID as a parameter and get back something like the following table. So, if I pass in 2 as my LocationID, I should get: Date | NumProductsDelivered | NumPermanentEmployees | NumSupportEmployees 10/10 | | 1 | 11/10 | 1 | 2 | 1 12/10 | 1 | 2 | 1 It seems like this should be a pretty simple query. I really don't even need the first table except as a way to fill in the combo box on the form from which the user chooses which location they want a report for. Unfortunately, everything I've done has resulted in me getting a lot more data than I should be getting. My confusion is in how to set up the join (presumably that's what I'm looking for here) given that I want both the date and locationID to be the same for each row in the result set. Any help would be much appreciated. Thanks.

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  • Showing an image after laoding it from sql database

    - by user330075
    I have a problem showing the image form database in a view Details and a ImageController. Inside the view i have: img src=Url.Action("GetFile","Image", new {id= Model.id}) and in controller: public FileContentResult GetFile(int idl) { //int idl = 32; SqlDataReader rdr; byte[] fileContent = null; ........... return File(,,); } When the view is called, function GetFile it just wont work,but if i cut out the parameter int id1 and i instantiate it as a variable it'l work. public FileContentResult GetFile() { int idl = 32; SqlDataReader rdr; byte[] fileContent = null; ........... return File(,,); } Why?

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  • Getting #Error value from ssrs reporting

    - by deepa
    I have created a dataset with fields "LastRunBuild" and "project" .The LastRunBuild field contain string of data seperated by commas according to each project. But Some Projects have no value in LastRunBuild field.When i am using this expression " iif(Fields!LastRunBuild.Value=nothing, nothing,Split(Fields!LastRunBuild.Value,",").GetValue(3)) " a #Error value returns every time. Please reply...

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  • SQLite: Simple DELETE statement did not work

    - by user186446
    I have a table MRU, that has 3 columns. (VALUE varchar(255); TYPE varchar(20); DT_ADD datetime) This is a table simply storing an entry and recording the date time it was recorded. What I wanted to do is: delete the oldest entry whenever I add a new entry that exceeds a certain number. here is my query: delete from MRU where type = 'FILENAME' ORDER BY DT_ADD limit 1; The query returns an error. Thanks

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  • how to order string logically

    - by just_name
    Q: I have the following case : set of letters (grades) A,A+,A-,B,B+,B- stored as strings in the database i wanna to order these grades logically from the small one to the big one ,, but this not what happen in real.. because these are strings the order is: A,A+,A- i wanna ASC A-,A,A+ DESC A+,A,A- i bind those grades in drop down list and i wanna these grades with this logical order in it.. is there any idea how to do something like this..

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  • Speeding up a group by date query on a big table in postgres

    - by zaius
    I've got a table with around 20 million rows. For arguments sake, lets say there are two columns in the table - an id and a timestamp. I'm trying to get a count of the number of items per day. Here's what I have at the moment. SELECT DATE(timestamp) AS day, COUNT(*) FROM actions WHERE DATE(timestamp) >= '20100101' AND DATE(timestamp) < '20110101' GROUP BY day; Without any indices, this takes about a 30s to run on my machine. Here's the explain analyze output: GroupAggregate (cost=675462.78..676813.42 rows=46532 width=8) (actual time=24467.404..32417.643 rows=346 loops=1) -> Sort (cost=675462.78..675680.34 rows=87021 width=8) (actual time=24466.730..29071.438 rows=17321121 loops=1) Sort Key: (date("timestamp")) Sort Method: external merge Disk: 372496kB -> Seq Scan on actions (cost=0.00..667133.11 rows=87021 width=8) (actual time=1.981..12368.186 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 32447.762 ms Since I'm seeing a sequential scan, I tried to index on the date aggregate CREATE INDEX ON actions (DATE(timestamp)); Which cuts the speed by about 50%. HashAggregate (cost=796710.64..796716.19 rows=370 width=8) (actual time=17038.503..17038.590 rows=346 loops=1) -> Seq Scan on actions (cost=0.00..710202.27 rows=17301674 width=8) (actual time=1.745..12080.877 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 17038.663 ms I'm new to this whole query-optimization business, and I have no idea what to do next. Any clues how I could get this query running faster?

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  • filter by atributs php script

    - by cosy
    I have the table : id id_products id_atribut name value 1 13 8 autdio 2.1 2 13 9 hdd 200 Gb 3 13 10 cd-rom 2 4 20 8 audio 2.1 the problem is, how can i select from this table where id_products=13 and name="audio" and value="2.1" and name="hdd" and value="200 gb" .... How can i do this?

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  • Firebird 2.1 + EXISTS = query bug?

    - by Atlas
    Using Delphi 2009 + Firebird 2.1.3. Database is ODS 11.1, default char set is UTF8. My prepared query is as follows: SELECT a.po_id, a.po_no FROM purchase_order a WHERE EXISTS (SELECT 1 FROM sales_order_item z1 JOIN purchase_order_item z2 ON z2.so_item_id = z1.so_item_id AND z2.po_id = a.po_id WHERE z1.so_id = :soid) ORDER BY a.po_no Now when I loop this say 1000 times because I have 1000 x so_id, the CPU usage get at 100% for FBSERVER.EXE Anyone encountered this problem?

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  • How to handle Foreign Keys with Entity Framework

    - by Jack Marchetti
    I have two entities. Groups. Pools. A Group can create many pools. So I setup my Pool table to have a GroupID foreign key. My code: using (entity _db = new entity()) { Pool p = new Pool(); p.Name = "test"; p.Group.ID = "5"; _db.AddToPool(p); } This doesn't work. I get a null reference exception on p.Group. How do I go about creating a new "Pool" and associating a GroupID?

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  • How to limit results by SUM

    - by superspace
    I have a table of events called event. For the purpose of this question it only has one field called date. The following query returns me a number of events that are happening on each date for the next 14 days: SELECT DATE_FORMAT( ev.date, '%Y-%m-%d' ) as short_date, count(*) as date_count FROM event ev WHERE ev.date >= NOW() GROUP BY short_date ORDER BY ev.start_date ASC LIMIT 14 The result could be as follows: +------------+------------+ | short_date | date_count | +------------+------------+ | 2010-03-14 | 1 | | 2010-03-15 | 2 | | 2010-03-16 | 9 | | 2010-03-17 | 8 | | 2010-03-18 | 11 | | 2010-03-19 | 14 | | 2010-03-20 | 13 | | 2010-03-21 | 7 | | 2010-03-22 | 2 | | 2010-03-23 | 3 | | 2010-03-24 | 3 | | 2010-03-25 | 6 | | 2010-03-26 | 23 | | 2010-03-27 | 14 | +------------+------------+ 14 rows in set (0.06 sec) Let's say I want to dislay these events by date. At the same time I only want to display a maximum of 10 at a time. How would I do this? Somehow I need to limit this result by the SUM of the date_count field but I do not know how. Anybody run into this problem before? Any help would be appreciated. Thanks

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  • How can I get the count of orders placed from my database?

    - by user1360564
    I am preparing a chart which will display the number of orders placed for a particular day in the current month and year. I wanted the count of orders placed for each day. I am showing the count of orders on the y-axis and the day on the x-axis. In my database, there is table called "order" in which order data is placed: order date, user_id, order_price, etc. For example, if on 4 July, 10 orders are placed, on 5 july, 20 orders are placed, and so on. How can I get the count of orders placed for day of the current month?

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  • Transfer Data between databases with postgres

    - by user227932
    I need to transfer some data from another Database. The old database is called paw1.moviesDB and the new database is paw1. The schema of each table are the following Awards (name of the table)(new DB) Id [PK] Serial Award Nominations (name of the table) (old DB) Id [PK] Serial nominations I want to copy the data from old DB to the new DB.

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  • What is the maximum length of a string parameter to Stored procedure?

    - by padmavathi
    I have a string of length 1,44,000 which has to be passed as a parameter to a stored procedure which is a select query on a table. When a give this is in a query (in c# ) its working fine. But when i pass it as a parameter to stored procedure its not working. Here is my stored procedure where in i have declared this parameter as NVARCHAR(MAX) ------------------------------------------------------ set ANSI_NULLS ON set QUOTED_IDENTIFIER ON go CREATE PROCEDURE [dbo].[ReadItemData](@ItemNames NVARCHAR(MAX),@TimeStamp as DATETIME) AS select * from ItemData where ItemName in (@ItemNames) AND TimeStamp=@TimeStamp --------------------------------------------------------------------- Here the parameter @ItemNames is a string concatinated with different names such as 'Item1','Item2','Item3'....etc. Can anyone tell what went wrong here? Thanks & Regards Padma

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