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• How to select product that have the maximum price of each category?

  - by kimleng

  The below is my table that has the item such as: ProductId ProductName Category Price 1 Tiger Beer $12.00 2 ABC Beer $13.99 3 Anchor Beer $9.00 4 Apolo Wine $10.88 5 Randonal Wine $18.90 6 Wisky Wine $30.19 7 Coca Beverage $2.00 8 Sting Beverage $5.00 9 Spy Beverage $4.00 10 Angkor Beer $12.88 And I suppose that I have only three category in this table (I can have a lot of category in this table). And I want to show the maximum product's price of each category in this table.

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• filter duplicates in SQL join

  - by Will

  When using a SQL join, is it possible to keep only rows that have a single row for the left table? For example: select * from A, B where A.id = B.a_id; a1 b1 a2 b1 a2 b2 In this case, I want to remove all except the first row, where a single row from A matched exactly 1 row from B. I'm using MySQL.

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• PHP-MySQL: Arranging rows from seperate tables together/Expression to determine row origin

  - by Koroviev

  I'm new to PHP and have a two part question. I need to take rows from two separate tables, and arrange them in descending order by their date. The rows do not correspond in order or number and have no relationship with each other. ---EDIT--- They each contain updates on a site, one table holds text, links, dates, titles etc. from a blog. The other has titles, links, specifications, etc. from images. I want to arrange some basic information (title, date, small description) in an updates section on the main page of the site, and for it to be in order of date. Merging them into one table and modifying it to suit both types isn't what I'd like to do here, the blog table is Wordpress' standard wp_posts and I don't feel comfortable adding columns to make it suit the image table too. I'm afraid it could clash with upgrading later on and it seems like a clumsy solution (but that doesn't mean I'll object if people here advise me it's the best solution). ------EDIT 2------ Here are the DESCRIBES of each table: mysql> describe images; +---------+--------------+------+-----+-------------------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+-------------------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | project | varchar(255) | NO | | NULL | | | title | varchar(255) | NO | | NULL | | | time | timestamp | NO | | CURRENT_TIMESTAMP | | | img_url | varchar(255) | NO | | NULL | | | alt_txt | varchar(255) | YES | | NULL | | | text | text | YES | | NULL | | | text_id | int(11) | YES | | NULL | | +---------+--------------+------+-----+-------------------+----------------+ mysql> DESCRIBE wp_posts; +-----------------------+---------------------+------+-----+---------------------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------------------+---------------------+------+-----+---------------------+----------------+ | ID | bigint(20) unsigned | NO | PRI | NULL | auto_increment | | post_author | bigint(20) unsigned | NO | | 0 | | | post_date | datetime | NO | | 0000-00-00 00:00:00 | | | post_date_gmt | datetime | NO | | 0000-00-00 00:00:00 | | | post_content | longtext | NO | | NULL | | | post_title | text | NO | | NULL | | | post_excerpt | text | NO | | NULL | | | post_status | varchar(20) | NO | | publish | | | comment_status | varchar(20) | NO | | open | | | ping_status | varchar(20) | NO | | open | | | post_password | varchar(20) | NO | | | | | post_name | varchar(200) | NO | MUL | | | | to_ping | text | NO | | NULL | | | pinged | text | NO | | NULL | | | post_modified | datetime | NO | | 0000-00-00 00:00:00 | | | post_modified_gmt | datetime | NO | | 0000-00-00 00:00:00 | | | post_content_filtered | text | NO | | NULL | | | post_parent | bigint(20) unsigned | NO | MUL | 0 | | | guid | varchar(255) | NO | | | | | menu_order | int(11) | NO | | 0 | | | post_type | varchar(20) | NO | MUL | post | | | post_mime_type | varchar(100) | NO | | | | | comment_count | bigint(20) | NO | | 0 | | +-----------------------+---------------------+------+-----+---------------------+----------------+ ---END EDIT--- I can do this easily with a single table like this (I include it here in case I'm using an over-elaborate method without knowing it): $content = mysql_query("SELECT post_title, post_text, post_date FROM posts ORDER BY post_date DESC"); while($row = mysql_fetch_array($content)) { echo $row['post_date'], $row['post_title'], $row['post_text']; } But how is it possible to call both tables into the same array to arrange them correctly? By correctly, I mean that they will intermix their echoed results based on their date. Maybe I'm looking at this from the wrong perspective, and calling them to a single array isn't the answer? Additionally, I need a way to form a conditional expression based on which table they came from, so that rows from table 1 get echoed differently than rows from table 2? I want results from table 1 to be echoed differently (with different strings concatenated around them, I mean) for the purpose of styling them differently than those from table two. And vice versa. I know an if...else statement would work here, but I have no idea how can I write the expression that would determine which table the row is from. All and any help is appreciated, thanks.

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• MySql - set of time stamped data (timestamp,event) calculating events per day

  - by Kevin Ohashi

  I have a table: id, datetime, event i also have table dates: date (Y-m-d format) the problem is some days don't have any events, I would like them to show 0 (or null) SELECT DATE_FORMAT(table.timestamp, '%Y-%m-%d') ydm, count(table.fkUID) FROM `table` where table.fkUID=$var group by ydm; is there some way to join or use conditional statements to make the result show: date|count ---------- 2010-05-23| 5 2010-05-24| 0 <--- this line just doesn't exist in my query. 2010-05-26| 3

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• sqlite3 date operations when joining two tables in a view?

  - by duncan

  In short, how to add minutes to a datetime from an integer located in another table, in one select statement, by joining them? I have a table P(int id, ..., int minutes) and a table S(int id, int p_id, datetime start) I want to generate a view that gives me PS(S.id, P.id, S.start + P.minutes) by joining S.p_id=P.id The problem is, if I was generating the query from the application, I can do stuff like: select datetime('2010-04-21 14:00', '+20 minutes'); 2010-04-21 14:20:00 By creating the string '+20 minutes' in the application and then passing it to sqlite. However I can't find a way to create this string in the select itself: select p.*,datetime(s.start_at, formatstring('+%s minutes', p.minutes)) from p,s where s.p_id=p.id; Because sqlite as far the documentation tells, does not provide any string format function, nor can I see any alternative way of expressing the date modifiers.

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• SQL Server 2005 Convert Ascii to Unicode (UTF-8 -> nvarchar)

  - by Guazz

  I have data in an nvarchar field with data in ascii format: "Zard Frères Guesta" How do I convert it to a readable(unicode) format in t-sql?

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• Django: How/Where to store a value for a session without unnecessary DB hits

  - by GerardJP

  Hi all, I have an extended userprofile with AUTH_PROFILE_MODULE (ref: http://tinyurl.com/yhracqq) I would like to set a user.is_guru() method similar to user.is_active(). This would results for al views (or rather templates) to e.g. disable/enable certain user messages, displaying of widgets, etc. The boolean is stored in the extended user profile model, but I want to avoid hitting the DB for every view. So the questions is .. Do I use a context_processor, a template tag, session_dict or what have you to, possible cached, store this info for the duration of the users visit. Note: I dont have performance issues, so it's definitely filed under premature optimization. I just want to avoid generating extra work in the future :). Any pointers are very welcome. Thanx and greetz! Gerard.

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• Better data-structure design

  - by Tempname

  Currently in my application I have a single table that is giving me a bit of trouble. The issue at hand is I have a value object that is mapped to this table. When the data is returned to me as an array of value objects, I have to then loop through this array and begin my recursion by matching the ParentID to parent ObjectID's. The column ParentID is either null (acts a parent) or it holds the value of an ObjectID. I know there has to be a better way to create this data structure so that I do not have to do recursive loops to match ParentID's with their ObjectID's. Any help with this is greatly appreciated. Here is the table in describe form: +----------------+------------------+------+-----+---------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +----------------+------------------+------+-----+---------------------+-----------------------------+ | ObjectID | int(11) unsigned | NO | PRI | NULL | auto_increment | | ObjectHeight | decimal(6,2) | NO | | NULL | | | ObjectWidth | decimal(6,2) | NO | | NULL | | | ObjectX | decimal(6,2) | NO | | NULL | | | ObjectY | decimal(6,2) | NO | | NULL | | | ObjectLabel | varchar(255) | NO | | NULL | | | TemplateID | int(11) unsigned | NO | MUL | NULL | | | ObjectTypeID | int(11) unsigned | NO | MUL | NULL | | | ParentID | int(11) unsigned | YES | MUL | NULL | | | CreationDate | datetime | YES | | 0000-00-00 00:00:00 | | | LastModifyDate | timestamp | YES | | NULL | on update CURRENT_TIMESTAMP | +----------------+------------------+------+-----+---------------------+-----------------------------+e

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• IF I have multiple candidate keys which one is a primary key and justify your choice ??

  - by zahrani

  Given R = { Account , Analyst , Assets, Broker, Client, Commission, Company, Dividend, Exchange, Investment, Office, Profile, Return, Risk_profile, Stock, Volume} and a set of functional dependencies F{fd1, fd2,fd3, fd4, fd5,fd6, fd7, fd8, fd9, fd10, fd11} where: fd1: Client - Office fd2: Stock - Exchange, Dividend fd3: Broker - Profile fd4: Company - Stock fd5: Client - Risk_profile, Analyst fd6: Analyst - Broker fd7: Stock, Broker - Invenstment, Volume fd8: Stock - Company fd9: Investment,Commission - Return fd10: Stock, Broker - Client fd11: Account - Assests these are candidate key(s) : (Account, Commission,Analyst ,Company) (Account, Commission,Analyst ,Stock) (Account ,Commission,Broker ,Company) (Account ,Commission,Broker ,Stock) (Account ,Commission,Client, Company) (Account ,Commission,Client ,Stock) (Q) Select a primary key and justify your choice ? I was select (Account ,Commission,Broker ,Stock) as a primary key ??? I chose that because it has the most direct dependencies compared to other ones. e.g. more attributes are functionally dependent on this primary key. please check if my answer is it true ? or Not I'm waiting your answer asap thank you

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• Physically cluster a MYSQL table for better performance

  - by ming yeow

  I have a 30M row table, which is indexed by ID now. However, a lot of the requests are around a much smaller subset, which is identified by app_user=1 Does it make sense to physically cluster the table according to this? If so, how can I do so?

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• "select * into table" Will it work for inserting data into existing table

  - by Shantanu Gupta

  I am trying to insert data from one of my existing table into another existing table. Is it possible to insert data into any existing table using select * into query. I think it can be done using union but in that case i need to record all data of my existing table into temporary table, then drop that table and finally than apply union to insert all records into same table eg. select * into #tblExisting from tblExisting drop table tblExisting select * into tblExisting from #tblExisting union tblActualData Here tblExisting is the table where I actually want to store all data tblActualData is the table from where data is to be appended to tblExisting. Is it right method. Do we have some other alternative ?

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• How to constrain a table linking two tables in many-to-many relationship

  - by Gromul

  Say I have the following tables and columns: comp: id, model dvd: id, model comp2dvd: id, id_comp, id_dvd A computer can have multiple dvd drives, even of the same model, and a dvd drive can appear in multiple computers. How do I make it so that comp2dvd table can have only existing comp and dvd ids? Thanks

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• Referencing surrogate key

  - by Arman

  I have a table that has an autoincrement surrogate key. I want to use it as a foreign key of my other table. The thing is, I cant figure out how I can reference it to that table, because it is nearly impossible to determine what I have to reference(the actual value of the surrogate key). Please be noted that what I am trying to do is adding a tuple/record through my program(outside the dbms). The process is: Add a new record in Table1 and generate an autoincrement key. Update Add a new record in Table2 and reference its foreign key to the primary key of Table1. Update My question is : HOW do I store the foreign key if I didnt know what is it?

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• Prroblem with ObjectDelete() in Entity Framework 4

  - by Tom

  I got two entities: public class User : Entity { public virtual string Username { get; set; } public virtual string Email { get; set; } public virtual string PasswordHash { get; set; } public virtual List<Photo> Photos { get; set; } } and public class Photo : Entity { public virtual string FileName { get; set; } public virtual string Thumbnail { get; set; } public virtual string Description { get; set; } public virtual int UserId { get; set; } public virtual User User { get; set; } } When I try to delete the photo it works fine for the DB (record gets romoved from the table) but it doesnt for the Photos collection in the User entity (I can still see that photo in user.Photos). This is my code. What I'm doing wrong here? Changing entity properties works fine. When I change photo FileName for example it gets updated in DB and in user.Photos. var photo = SelectById(id); Context.DeleteObject(photo); Context.SaveChanges(); var user = GetUser(userName); // the photo I have just deleted is still in user.Photos also tried this but getting same results: var photo = user.Photos.First(); Context.DeleteObject(photo); Context.SaveChanges();

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• Duplicating table in MYSQL without copying one row at a time

  - by ming yeow

  Hi folks, I want to duplicate a very large table, but I do not want to copy it row by row. Is there a way to duplicate it? For example, you can TRUNCATE w/o deleting row/row, so i was wondering if there is something similar for copying entire tables

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• diffing two databases

  - by flybywire

  Is there a tool to find the difference between two databases. Both the schema and the actual data are pretty much the same, but not 100%. Do you know a tool that can help to succinctly describe the changes.

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• How to store data of java array in Hard Disk, so as i can use it later?

  - by alindbillore

  Goodevening Sir/Mam, I am trying to make a small program that will be used for hotel room reservation, please tell me how to store the data of room's status on disk, as when we open the program next time we'll get the data. Please help i am very new here. Have a nice day!

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• has anyone produced an in-memory GIT repository?

  - by Andrew Matthews

  I would like to be able to take advantage of the benefits of GIT (and its workflows), but without the cost of disk access - I just would like to leverage the distributed revision control capabilities of GIT to produce something like a hybrid of memcached and GIT. (preferably in .NET) Is there such a beast out there?

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• Question about OOP and objects.

  - by loddn

  I have a school assignment, a Dog Show. My assignment is to create a website where vistors can display results and Judges and Secretary can admin, crud. I have a small problem one part of the assignment. The result should be based on two protokols from different judges and after that checked by the secretary before the result is displayed for the user. I have to say i'm fairly new to programming and so i need some smart suggestions on how to design and implement this. The assignment should cover both a db and c# (.net mvc). Q1: How do i create a object (result)that depends on two other objects(protocol)? Is that even needed? Q2: How to solve this in a relational db?

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• Query two tables from different schema

  - by Guru

  Hi- I have two different schemas in Oracle (say S1, S2). And two tables in those schemas(say S1.Table1, S2.Table2). I want to query these two tables from schema S1. Both S1 and S2 are in different databases. From DB1 - Schema S1, I want to do something like this, select T1.Id from S1.Table1 T1 , S2.Table2 T2 Where T1.Id = T2.refId I know one way of doing this would be creating a DB Link for the second schema and use it in querying. But sadly, I don't have priv to create DB link. Is there some way to do without DB link, like, in TOAD, you can compare two schema objects. But again, two schema objects and it is general comparision. Not like querying them. Any ideas, suggestions are greatly appriciated. Thanks in advance.

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• e-commerce product data/metadata schemas

  - by Shreko

  Trying to figure out how is product data/metadata schema designed. For example, how does an e-commerce site enter a product spec. Does it copy and paste from mfg spec sheet, enters it in their own fields or something else? Here is an example, looking at the D3000 Nikon DSLR Manufacturer: http://nikon.ca/en/Product.aspx?m=17300&disp=Specs futureshop.ca: www.futureshop.ca/en-CA/product/nikon-nikon-d3000-10-2mp-dslr-camera-with-18-55mm-lens-kit-d3000/10128435.aspx?path=865c2348a1542e848982c9dbd9253483en02 memoryexpress.com: www.memoryexpress.com/Products/PID-MX25539%28ME%29.aspx They are all slightly different in order or in parent/child field? What's storage is used for this type of info rdbms or xml?

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• "SQLSTATE[23000]: Integrity constraint violation" in Doctrine

  - by rags

  Hi, i do get an Integrity constraint violation for Doctrine though i really can't see why. Schema.yml User: columns: id: type: integer primary: true autoincrement: true username: type: varchar(64) notnull: true email: type: varchar(128) notnull: true password: type: varchar(128) notnull: true relations: Websites: class: Website local: id foreign: owner type: many foreignType: one onDelete: CASCADE Website: columns: id: type: integer primary: true autoincrement: true active: type: bool owner: type: integer notnull: true plz: type: integer notnull: true longitude: type: double(10,6) notnull: true latitude: type: double(10,6) notnull: true relations: Owner: type: one foreignType: many class: User local: owner foreign: id And here's my data Fixtures (data.yml) Model_User: User_1: username: as email: as****.com password: ***** Model_Website: Website_1: active: true plz: 34222 latitude: 13.12 longitude: 3.56 Owner: User_1

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• MySQL Throws NullReferenceException in Finalize... How are you coping with this?

  - by Cyril Gupta

  I am using MySQL with the .Net connector on 64 bit Windows. For some reason Mysql is throwing a NullReferenceException in Finalize. This is the problem here and it seems that its due to a bug described here. This bug was reported in 6.22, but I am getting the issue with 6.23 too so apparently it is not fixed. I am using MySQL both with the helper classes, and by instantiating the connection and the Mysqlcommand object. Does anybody have any idea what part of my code do I need to change to fix this issue? Cause even though this is a bug in Mysql this is not universal because I am not getting the problem in my other projects. MySQL bug report has no details on how to reproduce it either. Any suggestions?

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• Why are there so many DB management Systems ?

  - by mr.bio

  Hi there , i always asked myself. Why are there so many DB management systems? I am not an DB expert and i never thought about using another DB than mysql. Programming languages offer different paradigms, so there it makes sense to choose a specific language for your purpose. What are factors to choose a specific DB management system ?

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• 2 Select or 1 Join query ?

  - by xRobot

  I have 2 tables: book ( id, title, age ) ---- 100 milions of rows author ( id, book_id, name, born ) ---- 10 millions of rows Now, supposing I have a generic id of a book. I need to print this page: Title: mybook authors: Tom, Graham, Luis, Clarke, George So... what is the best way to do this ? 1) Simple join like this: Select book.title, author.name From book, author WHERE ( author.book_id = book.id ) AND ( book.id = 342 ) 2) For avoid the join, I could make 2 simple query: Select title FROM book WHERE id = 342 Select name FROM author WHERE book_id = 342 What is the most efficient way ?

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