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  • What are the Pros and Cons of Cascading delete and updates?

    - by Misnomer
    Hi, Maybe this is sort of a naive question...but I think that we should always have cascading deletes and updates. But I wanted to know are there problems with it and when should we should not do it? I really can't think of a case right now where you would not want to do an cascade delete but I am sure there is one...but what about updates should they be done always? So can anyone please list out the pros and cons of cascading deletes and updates ? Thanks.

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  • User has many computers, computers have many attributes in different tables, best way to JOIN?

    - by krismeld
    I have a table for users: USERS: ID | NAME | ---------------- 1 | JOHN | 2 | STEVE | a table for computers: COMPUTERS: ID | USER_ID | ------------------ 13 | 1 | 14 | 1 | a table for processors: PROCESSORS: ID | NAME | --------------------------- 27 | PROCESSOR TYPE 1 | 28 | PROCESSOR TYPE 2 | and a table for harddrives: HARDDRIVES: ID | NAME | ---------------------------| 35 | HARDDRIVE TYPE 25 | 36 | HARDDRIVE TYPE 90 | Each computer can have many attributes from the different attributes tables (processors, harddrives etc), so I have intersection tables like this, to link the attributes to the computers: COMPUTER_PROCESSORS: C_ID | P_ID | --------------| 13 | 27 | 13 | 28 | 14 | 27 | COMPUTER_HARDDRIVES: C_ID | H_ID | --------------| 13 | 35 | So user JOHN, with id 1 owns computer 13 and 14. Computer 13 has processor 27 and 28, and computer 13 has harddrive 35. Computer 14 has processor 27 and no harddrive. Given a user's id, I would like to retrieve a list of that user's computers with each computers attributes. I have figured out a query that gives me a somewhat of a result: SELECT computers.id, processors.id AS p_id, processors.name AS p_name, harddrives.id AS h_id, harddrives.name AS h_name, FROM computers JOIN computer_processors ON (computer_processors.c_id = computers.id) JOIN processors ON (processors.id = computer_processors.p_id) JOIN computer_harddrives ON (computer_harddrives.c_id = computers.id) JOIN harddrives ON (harddrives.id = computer_harddrives.h_id) WHERE computers.user_id = 1 Result: ID | P_ID | P_NAME | H_ID | H_NAME | ----------------------------------------------------------- 13 | 27 | PROCESSOR TYPE 1 | 35 | HARDDRIVE TYPE 25 | 13 | 28 | PROCESSOR TYPE 2 | 35 | HARDDRIVE TYPE 25 | But this has several problems... Computer 14 doesnt show up, because it has no harddrive. Can I somehow make an OUTER JOIN to make sure that all computers show up, even if there a some attributes they don't have? Computer 13 shows up twice, with the same harddrive listet for both. When more attributes are added to a computer (like 3 blocks of ram), the number of rows returned for that computer gets pretty big, and it makes it had to sort the result out in application code. Can I somehow make a query, that groups the two returned rows together? Or a query that returns NULL in the h_name column in the second row, so that all values returned are unique? EDIT: What I would like to return is something like this: ID | P_ID | P_NAME | H_ID | H_NAME | ----------------------------------------------------------- 13 | 27 | PROCESSOR TYPE 1 | 35 | HARDDRIVE TYPE 25 | 13 | 28 | PROCESSOR TYPE 2 | 35 | NULL | 14 | 27 | PROCESSOR TYPE 1 | NULL | NULL | Or whatever result that make it easy to turn it into an array like this [13] => [P_NAME] => [0] => PROCESSOR TYPE 1 [1] => PROCESSOR TYPE 2 [H_NAME] => [0] => HARDDRIVE TYPE 25 [14] => [P_NAME] => [0] => PROCESSOR TYPE 1

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  • In mysql, is "explain ..." always safe?

    - by tye
    If I allow a group of users to submit "explain $whatever" to mysql (via Perl's DBI using DBD::mysql), is there anything that a user could put into $whatever that would make any database changes, leak non-trivial information, or even cause significant database load? If so, how? I know that via "explain $whatever" one can figure out what tables / columns exist (you have to guess names, though) and roughly how many records are in a table or how many records have a particular value for an indexed field. I don't expect one to be able to get any information about the contents of unindexed fields. DBD::mysql should not allow multiple statements so I don't expect it to be possible to run any query (just explain one query). Even subqueries should not be executed, just explained. But I'm not a mysql expert and there are surely features of mysql that I'm not even aware of. In trying to come up with a query plan, might the optimizer actual execute an expression in order to come up with the value that an indexed field is going to be compared against? explain select * from atable where class = somefunction(...) where atable.class is indexed and not unique and class='unused' would find no records but class='common' would find a million records. Might 'explain' evaluate somefunction(...)? And then could somefunction(...) be written such that it modifies data?

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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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  • 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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  • Disable animations when ending search in iPhone

    - by camilo
    Hi. A quicky: is there a way to dismiss the keyboard and the searchDisplayController without animation? I was able to do it when the user presses "Cancel", but when the user presses the black "window thingy" above search field (only visible while the user hasn't inserted any text), the animation always occurs, even when I change the delegate functions. Is there a way to control this, or as an alternative, to disable the user to end searching by pressing the black window? Thanks in advance.

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  • DateTime in SqlServer VisualStudio C#

    - by menacheb
    Hi, I Have a DataBase in my project With Table named 'ProcessData' and columns named 'Start_At' (Type: DateTime) and 'End_At' (Type: DateTime) . When I try to enter a new record into this table, it enter the data in the following format: 'YYYY/MM/DD HH:mm', when I actualy want it to be in that format: 'YYYY/MM/DD HH:mm:ss' (the secondes dosen't apper). Does anyone know why, and what should I do in order to fix this? Here is the code I using: con = new SqlConnection("...."); String startAt = "20100413 11:05:28"; String endAt = "20100414 11:05:28"; ... con.Open();//open the connection, in order to get access to the database SqlCommand command = new SqlCommand("insert into ProcessData (Start_At, End_At) values('" + startAt + "','" + endAt + "')", con); command.ExecuteNonQuery();//execute the 'insert' query. con.Close(); Many thanks

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  • Select Columns Only if String length is greater than 2

    - by Zee-pro
    Similar Question may be asked but I am unable to find anything that fits my needs. How can I select only columns where string length is greater than 2 This is how much has done yet. SELECT * FROM Table1 WHERE (Table1.ID = @ID) Or something like WHERE (Table1.ID = @ID) AND (LEN(*) > 2) Thank for all of your help I have a Table, in which I have 35 columns and a User ID column, now I want to select and display information from only those columns which have 2 string. I Like to Select only columns which have 2 string and the defined ID by User not the Whole Row !! I hope I am making sense. Table Desired Result DI 35 Lesson 4 Maths Lesson 9 ICT Lesson 12 English

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  • select from multiple tables but ordering by a datetime field

    - by Chris Mccabe
    I have 3 tables that are unrelated (related that each contains data for a different social network). Each has a datetime field dated- I'm already grouping by hour as you can see below (this one below for linked_in) SELECT count(*), date_format(dated, '%Y:%m:%d %H') as hour FROM upd8r_linked_in_accts WHERE CAST(dated AS DATE) = '".$start_date."' GROUP BY hour I would like to know how to do a total across all 3 networks- the tables for the three are CREATE TABLE IF NOT EXISTS `upd8r_facebook_accts` ( `id` int(11) NOT NULL AUTO_INCREMENT, `owner_id` varchar(50) NOT NULL, `user_id` int(11) NOT NULL, `fb_id` bigint(30) NOT NULL, `dated` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=80 ; CREATE TABLE IF NOT EXISTS `upd8r_linked_in_accts` ( `id` int(11) NOT NULL AUTO_INCREMENT, `owner_id` varchar(50) NOT NULL, `user_id` int(11) NOT NULL, `linked_in` varchar(200) NOT NULL, `oauth_secret` varchar(100) NOT NULL, `first_count` int(11) NOT NULL, `second_count` int(11) NOT NULL, `dated` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=200 ; CREATE TABLE IF NOT EXISTS `upd8r_twitter_accts` ( `id` int(11) NOT NULL AUTO_INCREMENT, `owner_id` varchar(50) NOT NULL, `user_id` int(11) NOT NULL, `twitter` varchar(200) NOT NULL, `twitter_secret` varchar(100) NOT NULL, `dated` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=9 ; something like this ? (SELECT count(*), date_format(dated, '%Y:%m:%d %H') as hour FROM upd8r_linked_in_accts WHERE CAST(dated AS DATE) = '".$start_date."') UNION ALL (SELECT count(*), date_format(dated, '%Y:%m:%d %H') as hour FROM upd8r_facebook_accts WHERE CAST(dated AS DATE) = '".$start_date."') UNION ALL (SELECT count(*), date_format(dated, '%Y:%m:%d %H') as hour FROM upd8r_twitter_accts WHERE CAST(dated AS DATE) = '".$start_date."') UNION ALL GROUP BY hour

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  • UUID collision risk using different algorithms

    - by Diego Jancic
    Hi Guys, I have a database where 2 (or maybe 3 or 4) different applications are inserting information. The new information has IDs of the type GUID/UUID, but each application is using a different algorithm to generate the IDs. For example, one is using the NHibernate's "guid.comb", other is using the SQLServer's NEWID(), other might want to use .NET's Guid.NewGuid() implementation. Is there an above normal risk of ID collision or duplicates? Thanks!

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  • Problem with checkboxes, sql select statements & php

    - by smokey20
    I am trying to display some rows from a database table based on choices submitted by the user. Here is my form code <form action="choice.php" method="POST" > <input type="checkbox" name="variable[]" value="Apple">Apple <input type="checkbox" name="variable[]" value="Banana">Banana <input type="checkbox" name="variable[]" value="Orange">Orange <input type="checkbox" name="variable[]" value="Melon">Melon <input type="checkbox" name="variable[]" value="Blackberry">Blackberry From what I understand I am placing the values of these into an array called variable. Two of my columns are called receipe name and ingredients(each field under ingredients can store a number of fruits). What I would like to do is, if a number of checkboxes are selected then the receipe name/s is displayed. Here is my php code. <?php // Make a MySQL Connection mysql_connect("localhost", "*****", "*****") or die(mysql_error()); mysql_select_db("****") or die(mysql_error()); $variable=$_POST['variable']; foreach ($variable as $variablename) { echo "$variablename is checked"; } $query = "SELECT receipename FROM fruit WHERE $variable like ingredients"; $row = mysql_fetch_assoc($result); foreach ($_POST['variabble'] as $ingredients) echo $row[$ingredients] . '<br/>'; ?> I am very new to php and just wish to display the data, I do not need to perform any actions on it. I have tried many select statements but I cannot get any results to display. My db connection is fine and it does print out what variables are checked. Many thanks in advance.

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  • alter mysqldump file before import

    - by julio
    Hi-- I have a mysqldump file created from an earlier version of a product that can't be imported into a new version of the product, since the db structure has changed slightly (mainly altering a column that was NOT NULL DEFAULT 0 to UNIQUE KEY DEFAULT NULL). If I just import the old dump file, it will error out since the column that has default values of 0 now breaks the UNIQUE constraint. It would be easy enough to either manually alter the mysqldump file, or import into a temp table and change it, then copy to the new table. However, is there a way to do this programatically, so it will be repeatable and not manual? (this will need to happen for many instances of this product). I'm thinking something like disabling key constraints for the import, then setting all values that = 0 to NULL, then re-enabling the key constraints? Is this possible? Any help appreciated.

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  • MD5 hash validation failing for unknown reason in PHP

    - by Sennheiser
    I'm writing a login form, and it converts the given password to an MD5 hash with md5($password), then matches it to an already-hashed record in my database. I know for sure that the database record is correct in this case. However, it doesn't log me in and claims the password is incorrect. Here's my code: $password = mysql_real_escape_string($_POST["password"]); ...more code... $passwordQuery = mysql_fetch_row(mysql_query(("SELECT password FROM users WHERE email = '$userEmail'"))); ...some code... elseif(md5($password) != $passwordQuery) { $_SESSION["noPass"] = "That password is incorrect."; } ...more code after... I tried pulling just the value of md5($password) and that matched up when I visually compared it. However, I can't get the comparison to work in PHP. Perhaps it is because the MySQL record is stored as text, and the MD5 is something else?

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  • Designing a table to store EXIF data

    - by rafale
    I'm looking to get the best performance out of querying a table containing EXIF data. The queries in question will only search the EXIF data for the specified strings and return the row index on a match. With that said, would it better to store the EXIF data in a table with separate columns for each of the tags, or would storing all of the tags in a single column as one long delimited string suit me just as well? There are around 115 EXIF tags I'll be storing, and each record would be around 1500 to 2000 chars in length if concatenated into a single string.

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  • How big teams work with database

    - by Michael Riva
    Lets say I have a team, 20 developers. And we are making a project on .net. In team every one can easy create their tables according to their modules working on it. And we think to use an ORM, can you tell me how can and which ORM tools for good to working with team. Is there any proven way? I m asking becouse I never work with a team, so I dont know the best practices. So you guys what kind of pattern you use?. I realy wonder. The team members can write their unit tests and supply necessary design patterns. What kind of approach I need to create to manage team? What kind of ORM tools that we have to use?

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  • Parse both symbols . and , as decimal digits delimiter in ASP.NET

    - by abatishchev
    I'm writing a banking system and my customer wants support both Russian and American numeric standards in decimal digits delimiter. Respectively . and ,. Now only , works properly. Perhaps because of web server's OS format (Russian is set). String like 2000.00 throws a FormatException: Input string was not in a correct format. How to fix that? Are there any other ideas except String.Replace('.', ',') on FormView.ItemInserting event?

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  • Java: JPQL search -similar- strings

    - by bguiz
    What methods are there to get JPQL to match similar strings? By similar I mean: Contains: search string is found within the string of the matches entity Case-insensitive Small mispellings: e.g. "arow" matches "arrow" I suspect the first two will be easy, however, I would appreciate help with the last one Thank you

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  • Circular database relationships. Good, Bad, Exceptions?

    - by jim
    I have been putting off developing this part of my app for sometime purely because I want to do this in a circular way but get the feeling its a bad idea from what I remember my lecturers telling me back in school. I have a design for an order system, ignoring the everything that doesn't pertain to this example I'm left with: CreditCard Customer Order I want it so that, Customers can have credit cards (0-n) Customers have orders (1-n) Orders have one customer(1-1) Orders have one credit card(1-1) Credit cards can have one customer(1-1) (unique ids so we can ignore uniqueness of cc number, husband/wife may share cc instances ect) Basically the last part is where the issue shows up, sometimes credit cards are declined and they wish to use a different one, this needs to update which their 'current' card is but this can only change the current card used for that order, not the other orders the customer may have on disk. Effectively this creates a circular design between the three tables. Possible solutions: Either Create the circular design, give references: cc ref to order, customer ref to cc customer ref to order or customer ref to cc customer ref to order create new table that references all three table ids and put unique on the order so that only one cc may be current to that order at any time Essentially both model the same design but translate differently, I am liking the latter option best at this point in time because it seems less circular and more central. (If that even makes sense) My questions are, What if any are the pros and cons of each? What is the pitfalls of circular relationships/dependancies? Is this a valid exception to the rule? Is there any reason I should pick the former over the latter? Thanks and let me know if there is anything you need clarified/explained. --Update/Edit-- I have noticed an error in the requirements I stated. Basically dropped the ball when trying to simplify things for SO. There is another table there for Payments which adds another layer. The catch, Orders can have multiple payments, with the possibility of using different credit cards. (if you really want to know even other forms of payment). Stating this here because I think the underlying issue is still the same and this only really adds another layer of complexity.

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  • MySQL query using multiple criteria from checkboxes

    - by jungle_programmer
    I would like to do a multiple search query usig multiple checkboxes which represent particular textboxes. How do i create a mysql query which will be filtering the checked and unchecked checkboxes (probably using if statements)? The query should be able to filter the checked and ucnchecked boxes and query them using the AND condition. Thanks

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  • error in arabic script in mysql

    - by fusion
    i inserted data in mysql database which includes arabic script. while the output displays arabic correctly, the data in mysql looks like garbage. something like this: '&#1589;&#1614;&#1608;&#1605;&#1615; &#1579;&#1614;&#1604;&#1575;&#1579;&#1614;&#1577;&#1616; &#1571;&#1610;&#1617;&#1575;&#1605;&#1613; &#1605;&#1616;&#1606; &#1603;&#1615;&#1604;&#1617;&#1616; &#1588;&#1614;&#1607;&#1585;&#1613; &#1600; &#1571;&#1585;&#1576;&#1614;&#1593;&#1575;&#1569;&#1615; &#1576;&#1614;&#1610;&#1606;&#1614; &#1582;&#1614; should i be worried about this? if yes, how do i make it appear in proper arabic script in mysql? thanks.

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  • Is there an alternative to Microsoft.SqlServer.Management.Smo.SqlDataType that includes a value for

    - by Daniel Schaffer
    The Microsoft.SqlServer.Management.Smo.SqlDataType enum has a value for the timestamp type but not rowversion. I'm looking for an updated version of the assembly or an alternate enum type that supports it. The existing enum has a value for Timestamp, but according to the rowversion documentation, timestamp is "deprecated and will be removed in a future version". I prefer to avoid using deprecated things :)

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  • Using a comma seperated data in MYSQL "IN" clause

    - by Sashi Kant
    I have a column in one of my table where I store multiple ids seperated by comma's. Is there a way in which I can use this column's value in the "IN" clause of a query. The column(city) has values like 6,7,8,16,21,2 I need to use as Select * from table where e_ID in (Select city from locations where e_Id=?) I am satisfied with Crozin's answer, but I am open to suggestions, views and options. Feel free to share your views.

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  • How can I "merge", "flatten" or "pivot" results from a query which returns multiple rows into a sing

    - by dsm
    I have a simple query over a table, which returns results like the following: id id_type id_ref 2702 5 31 2702 16 14 2702 17 3 2702 40 1 2702 26 4 And I would like to merge the results into a single row, for instance: id concatenation 2702 5,16,17,40,26:31,14,3,1,4 Is there any way to do this within a trigger? NB: I know I can use a cursor, but I would really prefer not to unless there is no better way.

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