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• Is there a difference using join andselect from multi-tables?

  - by nemiss

  First option: SELECT Table1.* ,Table2.Price AS Price FROM Table1,Table2 WHERE Table1.ID = Table2.ID Second option: SELECT Table1.* ,Table2.Price AS Price FROM Table1 INNER JOIN Table2 ON Table1.ID = Table2.ID Which one is better and most efficient?

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• Get the first and last posts in a thread

  - by Grampa

  I am trying to code a forum website and I want to display a list of threads. Each thread should be accompanied by info about the first post (the "head" of the thread) as well as the last. My current database structure is the following: threads table: id - int, PK, not NULL, auto-increment name - varchar(255) posts table: id - int, PK, not NULL, auto-increment thread_id - FK for threads The tables have other fields as well, but they are not relevant for the query. I am interested in querying threads and somehow JOINing with posts so that I obtain both the first and last post for each thread in a single query (with no subqueries). So far I am able to do it using multiple queries, and I have defined the first post as being: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id LIMIT 0, 1 The last post is pretty much the same except for ORDER BY id DESC. Now, I could select multiple threads with their first or last posts, by doing: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id GROUP BY t.id But of course I can't get both at once, since I would need to sort both ASC and DESC at the same time. What is the solution here? Is it even possible to use a single query? Is there any way I could change the structure of my tables to facilitate this? If this is not doable, then what tips could you give me to improve the query performance in this particular situation?

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• .NET/C# Drizzle database client

  - by FlappySocks

  I am planning to use Drizzle in my next C# Mono app. Since there is no C# client available for Drizzle, I thought I would have a stab at writing my own by converting the Java client, and then making it work with DBLinq. Having seen the Java client, I realise that it's a longer job that I had anticipated, and I don't have the time. Besides the Java client is not all that mature yet. Since there is an official Drizzle C client library (libdrizzle), writing a C# wrapper might be the best solution. Are there any tools available that can assist in generating the code for this?

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• Right way to implement a n-to-m related

  - by ThreeFingerMark

  Hello, this is a part from my database structure: Table: Item Columns: ItemID, Title, Content, Price Table: Tag Columns: TagID, Title Table: ItemTag Columns: ItemID, TagID Table: Image Columns: ImageID, Path, Size, UploadDate Table: ItemImage Columns: ItemID, ImageID The items can have more than one image so i have a extra table "Image" and map this images to an items. I see now a problem with this structure. Before i can add Images i must enter an item. My question is now. Is this structure a good way to solve my problem with many images / tags for one item? Thank you

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• oracle search word in string

  - by Atul

  I want to search a word in string in ORACLE in which string is comma separated. Eg. String is ('MF1,MF2,MF3') and now I want to search whether 'MF' exists in that or not. If I am using instr('MF1,MF2,MF3','MF') it will give wrong result since I want to search Full MF in MF1 or MF2 or MF3.

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• SQLParameter not working properly

  - by Pselus

  I am trying to access a stored procedure and I'm getting an error that says: Procedure or function 'getbug' expects parameter '@bugID', which was not supplied. This is my code to call the procedure. SqlCommand cmd = new SqlCommand("getbug", cn); cmd.Parameters.Add(new SqlParameter("bugID", bugID)); bugID is set as 1089 (and is type int) I can't figure out why this won't work.

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• MySQL Query, how to group and count in one row ?

  - by Akarun

  Hi All, To simplify, I have tree tables: products, products-vs-orders, orders products fields : 'ProductID', 'Name', 'isGratis', ... products-vs-orders fields : 'ProductID', 'OrderID' orders fields : 'OrderID', 'Title', ... Actually, I have a query like this: SELECT orders.OrderID, orders.Title, COUNT(`products`.`isGratis`) AS "Quantity", `products`.`isGratis` FROM `orders`, `products-vs-orders`, `products` WHERE `orders`.`OrderID` = `products-vs-orders`.`OrderID` AND `products-vs-orders`.`ProductID` = `products`.`ProductID` GROUP BY `products`.`PackID`, `products`.`isGratis` This query works and return this surch of result: OrderID, Title, Quantity, isGratis 1 My Order 20 0 1 My Order 3 1 2 An other 8 0 2 An other 1 1 How can I retrieve the count of products 'gratis' and 'paid' in to separate cols ? OrderID, Title, Qt Paid, Qt Gratis 1 My Order 20 3 2 An other 8 1 Thanks for your help

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• Why is doing a top(1) on an indexed column in mssql slow?

  - by reinier

  I'm puzzled by the following. I have a DB with around 10 million rows, and (among other indices) on 1 column is an index. Now I have 700k rows where the campaignid is indeed 3835 For all these rows, the connectionid is the same. I just want to find out this connectionid. use messaging_db; SELECT TOP (1) connectionid FROM outgoing_messages WITH (NOLOCK) WHERE (campaignid_int = 3835) Now this query takes approx 30 seconds to perform! I (with my small db knowledge) would expect that it would take any of the rows, and return me that connectionid If I test this same query for a campaign which only has 1 entry, it goes really fast. So the index works. How would I tackle this and why does this not work?

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• Deleting rows from different tables

  - by Ross

  Here is what i'm trying to do: Delete the project from projects table and all the images associated with that project in the images table Lets say $del_id = 10 DELETE FROM projects, images WHERE projects.p_id = '$del_id' AND images.p_id = '$del_id' What is wrong with this query

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• How do I select a fixed number of rows for each group?

  - by Maiasaura

  Here is some example data in a mysql table a b distance 15 44 250 94 31 250 30 41 250 6 1 250 95 18 250 72 84 500 14 23 500 55 24 500 95 8 500 59 25 500 40 73 500 65 85 500 32 50 500 31 39 500 22 25 500 37 11 750 98 39 750 15 57 750 9 22 750 14 44 750 69 22 750 62 50 750 89 35 750 67 65 750 74 37 750 52 36 750 66 53 750 82 74 1000 79 22 1000 98 41 1000 How do I query this table such that I get 2 rows per distance selected at random? A successful query will produce something like a b distance 30 41 250 95 18 250 59 25 500 65 85 500 15 57 750 89 35 750 79 22 1000 98 41 1000

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• Databinding expression for retrieving value of related collection using LINQ

  - by joshb

  I have a GridView that is bound to a LINQDataSource control that is returning a collection of customers. Within my DataGrid I need to display the home phone number of a customer, if they have one. The phone numbers of a customer are stored in a separate table with a foreign key pointing to the customer table. The following binding expression gets me the first phone number for a customer: <asp:TemplateField HeaderText="LastName" SortExpression="LastName"> <ItemTemplate> <asp:Label ID="PhoneLabel" runat="server" Text='<%# Eval("Phones[0].PhoneNumber") %>'></asp:Label> </ItemTemplate> </asp:TemplateField> I need to figure out how to get the home phone number specifically (filter based on phone type) and handle the scenario where the customer does not have a home phone in the database. Right now it's throwing an out of range exception if the customer does not have any phone numbers. I've tried using the Where operator with a lambda expression to filter the phone type but it doesn't work: <%# Eval("Phones.Where(p => p.PhoneTypeId == 2).PhoneNumber") %> Solutions or links to any good articles on the subject would be much appreciated.

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• How do I create a multiple-table check constraint?

  - by Zack Peterson

  Please imagine this small database... Diagram Tables Volunteer Event Shift EventVolunteer ========= ===== ===== ============== Id Id Id EventId Name Name EventId VolunteerId Email Location VolunteerId Phone Day Description Comment Description Start End Associations Volunteers may sign up for multiple events. Events may be staffed by multiple volunteers. An event may have multiple shifts. A shift belongs to only a single event. A shift may be staffed by only a single volunteer. A volunteer may staff multiple shifts. Check Constraints Can I create a check constraint to enforce that no shift is staffed by a volunteer that's not signed up for that shift's event? Can I create a check constraint to enforce that two overlapping shifts are never staffed by the same volunteer?

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• How do I drop a foerign key in mssql?

  - by mmattax

  I have created a foreign key (in mssql / tsql) by: alter table company add CountryID varchar(3); alter table company add constraint Company_CountryID_FK foreign key(CountryID) references Country; I then run this query: alter table company drop column CountryID; and I get this error: Msg 5074, Level 16, State 4, Line 2 The object 'Company_CountryID_FK' is dependent on column 'CountryID'. Msg 4922, Level 16, State 9, Line 2 ALTER TABLE DROP COLUMN CountryID failed because one or more objects access this column. I have tried this, yet it does not seem to work: alter table company drop foreign key Company_CountryID_FK; alter table company drop column CountryID; What do I need to do to drop the CountryID column? Thanks.

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• Insert not working

  - by user1642318

  I've searched evreywhere and tried all suggestions but still no luck when running the following code. Note that some code is commented out. Thats just me trying different things. SqlConnection connection = new SqlConnection("Data Source=URB900-PC\SQLEXPRESS;Initial Catalog=usersSQL;Integrated Security=True"); string password = PasswordTextBox.Text; string email = EmailTextBox.Text; string firstname = FirstNameTextBox.Text; string lastname = SurnameTextBox.Text; //command.Parameters.AddWithValue("@UserName", username); //command.Parameters.AddWithValue("@Password", password); //command.Parameters.AddWithValue("@Email", email); //command.Parameters.AddWithValue("@FirstName", firstname); //command.Parameters.AddWithValue("@LastName", lastname); command.Parameters.Add("@UserName", SqlDbType.VarChar); command.Parameters["@UserName"].Value = username; command.Parameters.Add("@Password", SqlDbType.VarChar); command.Parameters["@Password"].Value = password; command.Parameters.Add("@Email", SqlDbType.VarChar); command.Parameters["@Email"].Value = email; command.Parameters.Add("@FirstName", SqlDbType.VarChar); command.Parameters["@FirstName"].Value = firstname; command.Parameters.Add("@LasttName", SqlDbType.VarChar); command.Parameters["@LasttName"].Value = lastname; SqlCommand command2 = new SqlCommand("INSERT INTO users (UserName, Password, UserEmail, FirstName, LastName)" + "values (@UserName, @Password, @Email, @FirstName, @LastName)", connection); connection.Open(); command2.ExecuteNonQuery(); //command2.ExecuteScalar(); connection.Close(); When I run this, fill in the textboxes and hit the button I get...... Must declare the scalar variable "@UserName". Any help would be greatly appreciated. Thanks.

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• MSSQL - Select one random record not showing duplicates

  - by Lukes123

  I have two tables, events and photos, which relate together via the 'Event_ID' column. I wish to select ONE random photo from each event and display them. How can I do this? I have the following which displays all the photos which are associated. How can I limit it to one per event? SELECT Photos.Photo_Id, Photos.Photo_Path, Photos.Event_Id, Events.Event_Title, Events.Event_StartDate, Events.Event_EndDate FROM Photos, Events WHERE Photos.Event_Id = Events.Event_Id AND Events.Event_EndDate < GETDATE() AND Events.Event_EndDate IS NOT NULL AND Events.Event_StartDate IS NOT NULL ORDER BY NEWID() Thanks Luke Stratton

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• how to write this query using joins?

  - by aquero

  Hi, i have a table campaign which has details of campaign mails sent. campaign_table: campaign_id campaign_name flag 1 test1 1 2 test2 1 3 test3 0 another table campaign activity which has details of campaign activities. campaign_activity: campaign_id is_clicked is_opened 1 0 1 1 1 0 2 0 1 2 1 0 I want to get all campaigns with flag value 3 and the number of is_clicked columns with value 1 and number of columns with is_opened value 1 in a single query. ie. campaign_id campaign_name numberofclicks numberofopens 1 test1 1 1 2 test2 1 1 I did this using sub-query with the query: select c.campaign_id,c.campaign_name, (SELECT count(campaign_id) from campaign_activity WHERE campaign_id=c.id AND is_clicked=1) as numberofclicks, (SELECT count(campaign_id) from campaign_activity WHERE campaign_id=c.id AND is_clicked=1) as numberofopens FROM campaign c WHERE c.flag=1 But people say that using sub-queries are not a good coding convention and you have to use join instead of sub-queries. But i don't know how to get the same result using join. I consulted with some of my colleagues and they are saying that its not possible to use join in this situation. Is it possible to get the same result using joins? if yes, please tell me how.

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• Oracle: What does `(+)` do in a WHERE clause?

  - by Jonathan Lonowski

  Found the following in an Oracle-based application that we're migrating (generalized): SELECT Table1.Category1, Table1.Category2, count(*) as Total, count(Tab2.Stat) AS Stat FROM Table1, Table2 WHERE (Table1.PrimaryKey = Table2.ForeignKey(+)) GROUP BY Table1.Category1, Table1.Category2 What does (+) do in a WHERE clause? I've never seen it used like that before.

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• How to speed up a slow UPDATE query

  - by Mike Christensen

  I have the following UPDATE query: UPDATE Indexer.Pages SET LastError=NULL where LastError is not null; Right now, this query takes about 93 minutes to complete. I'd like to find ways to make this a bit faster. The Indexer.Pages table has around 506,000 rows, and about 490,000 of them contain a value for LastError, so I doubt I can take advantage of any indexes here. The table (when uncompressed) has about 46 gigs of data in it, however the majority of that data is in a text field called html. I believe simply loading and unloading that many pages is causing the slowdown. One idea would be to make a new table with just the Id and the html field, and keep Indexer.Pages as small as possible. However, testing this theory would be a decent amount of work since I actually don't have the hard disk space to create a copy of the table. I'd have to copy it over to another machine, drop the table, then copy the data back which would probably take all evening. Ideas? I'm using Postgres 9.0.0. UPDATE: Here's the schema: CREATE TABLE indexer.pages ( id uuid NOT NULL, url character varying(1024) NOT NULL, firstcrawled timestamp with time zone NOT NULL, lastcrawled timestamp with time zone NOT NULL, recipeid uuid, html text NOT NULL, lasterror character varying(1024), missingings smallint, CONSTRAINT pages_pkey PRIMARY KEY (id ), CONSTRAINT indexer_pages_uniqueurl UNIQUE (url ) ); I also have two indexes: CREATE INDEX idx_indexer_pages_missingings ON indexer.pages USING btree (missingings ) WHERE missingings > 0; and CREATE INDEX idx_indexer_pages_null ON indexer.pages USING btree (recipeid ) WHERE NULL::boolean; There are no triggers on this table, and there is one other table that has a FK constraint on Pages.PageId.

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• sql query returns incorrect result

  - by reza saberi

  I have a mysql database that stores quotation documents with some products that are clearly defining the price of each product in them, and a table for contracts storing contract details as well as customer code and quotation code to which it belongs. I have the following query to see how much is the total price of the quotation to write it in the invoice: select sum(sqproducts.price * sqproducts.quantity) as 'total-price', squotations.currency as 'currency' from sqproducts, ccontracts, squotations where sqproducts.contracted=1 AND squotations.code=sqproducts.quotation_code AND sqproducts.quotation_code=ccontracts.squotation_code AND sqproducts.quotation_code='QUOT/2012/1' group by currency

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• Calculate open timeslots given availability and existing appointments - by day

  - by Andre

  Overview: I have a table which stores a persons "availability" for a current day, e.g. Mon - 8:00am - 11:30am Mon - 1:30pm - 6:00pm A second table stores appointments that this person already has for the same day, e.g. Mon - 8:30am - 11:00am Mon - 2:30pm - 4pm Desired result: Doing calculationsI'd like to have the following result - e.g. "this person has availability on the given day": Mon - 8:00am - 8:30am Mon - 11:00am - 11:30am Mon - 1:30pm - 2:30pm Mon - 4:00pm - 6:00pm Any ideas on how to calculate the output given the two inputs (e.g. availability, existing appointments) would be greatly appreciated. Preferably I'd use javascript on the client to do the calculating as I would believe that doing it within the DB (I'm using MSSQL) would be slow for many records, persons, etc. Hope this is enough information to illustrate the problem at hand - Many thanks in advance.

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• Android quotes within an sql query string

  - by miannelle

  I want to perform a query like the following: uvalue = EditText( some user value ); p_query = "select * from mytable where name_field = '" + uvalue + "'" ; mDb.rawQuery( p_query, null ); if the user enters a single quote in their input it crashes. If you change it to: p_query = "select * from mytable where name_field = \"" + uvalue + "\"" ; it crashes if the user enters a double quote in their input. and of course they could always enter both single and double quotes.

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• What nosql means? can someone explain it to me in simple words?

  - by Amr ElGarhy

  in this post Stack Overflow Architecture i read about something called nosql, i didn't understand what it means, and i tried to search on google but seams that i can't get exactly whats it. Can anyone explain what nosql means in simple words?

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• iBatis how to solve a more complex N+1 problem

  - by Alvin

  I have a database that is similar to the following: create table Store(storeId) create table Staff(storeId_fk, staff_id, staffName) create table Item(storeId_fk, itme_id, itemName) The Store table is large. And I have create the following java bean public class Store { List<Staff> myStaff List<Item> myItem .... } public class Staff { ... } public class Item { ... } My question is how can I use iBatis's result map to EFFICIENTLY map from the tables to the java object? I tried: <resultMap id="storemap" class="my.example.Store"> <result property="myStaff" resultMap="staffMap"/> <result property="myItem" result="itemMap"/> </resultMap> (other maps omitted) But it's way too slow since the Store table is VERY VERY large. I tried to follow the example in Clinton's developer guide for the N+1 solution, but I cannot warp my mind around how to use the "groupBy" for an object with 2 list... Any help is appreciated!

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• What does DataContext.GetTable<TEntry> do?

  - by Bryan

  Consider I have a DataContext db, and there is an Entity class User. So when System.Data.Linq.Table<User> table = db.GetTable<User>(); is called for the first time, does it pull the data from the database immediately, does it use deferred execution, or were the data already loaded from database when db was initialized?

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• jpa join query on a subclass

  - by Brian

  I have the following relationships in JPA (hibernate). Object X has two subclasses, Y and Z. Object A has a manyToOne relationship to object X. (Note, this is a one-sided relationship so object X cannot see object A). Now, I want to get the max value of a column in object A, but only where the relationship is of a specific subtype, ie...Y. So, that equates to...get the max value of column1 in object A, across all instances of A where they have a relationship with Y. Is this possible? I'm a bit lost as how to query it. I was thinking of something like: String query = "SELECT MAX(a.columnName) FROM A a join a.x; Query query = super.entityManager.createQuery(query); query.execute(); However that doesn't take account of the subclass of X...so I'm a bit lost. Any help would be much appreciated.

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