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  • Is it compulsory to learn about Data Structures if you want to be a Java/C++ programmer ?

    - by happysoul
    So do I like really need to learn about them ? Isn't there an interesting way to learn about stacks, linked lists, heaps ,etc ? I found it a boring subject. **While posting this question it showed some warning.Am I not allowed to post such a question ? Admins please clarify and I will delete it :/ Warning :: The question you're asking appears subjective and is likely to be closed.

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  • Why is selecting specified columns, and all, wrong in Oracle SQL?

    - by TomatoSandwich
    Say I have a select statement that goes.. select * from animals That gives a a query result of all the columns in the table. Now, if the 42nd column of the table animals is is_parent, and I want to return that in my results, just after gender, so I can see it more easily. But I also want all the other columns. select is_parent, * from animals This returns ORA-00936: missing expression. The same statement will work fine in Sybase, and I know that you need to add a table alias to the animals table to get it to work ( select is_parent, a.* from animals ani), but why must Oracle need a table alias to be able to work out the select?

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  • How to group rows into two groups in sql?

    - by user1055638
    Lets say I have such a table: id|time|operation 1 2 read 2 5 write 3 3 read 4 7 read 5 2 save 6 1 open and now I would like to do two things: Divide all these records into two groups: 1) all rows where operation equals to "read" 2) all other rows. Sum the time in each group. So that my query would result only into two rows. What I got so far is: select sum(time) as total_time, operation group by operation ; Although that gives me many groups, depending on the number of distinct operations. How I could group them only into two categories? Cheers!

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  • Add to exisiting db values, rather than overwrite - PDO

    - by sam
    Im trying to add to existing decimal value in table, for which im using the sql below: UPDATE Funds SET Funds = Funds + :funds WHERE id = :id Im using a pdo class to handle my db calls, with the method below being used to update the db, but i couldnt figure out how to amend it to output the above query, any ideas ? public function add_to_values($table, $info, $where, $bind="") { $fields = $this->filter($table, $info); $fieldSize = sizeof($fields); $sql = "UPDATE " . $table . " SET "; for($f = 0; $f < $fieldSize; ++$f) { if($f > 0) $sql .= ", "; $sql .= $fields[$f] . " = :update_" . $fields[$f]; } $sql .= " WHERE " . $where . ";"; $bind = $this->cleanup($bind); foreach($fields as $field) $bind[":update_$field"] = $info[$field]; return $this->run($sql, $bind); }

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  • SQL Server 2005: Why would a delete from a temp table hang forever?

    - by Dr. Zim
    DELETE FROM #tItem_ID WHERE #tItem_ID.Item_ID NOT IN (SELECT DISTINCT Item_ID FROM Item_Keyword JOIN Keyword ON Item_Keyword.Keyword_ID = Keyword.Record_ID WHERE Keyword LIKE @tmpKW) The Keyword is %macaroni%. Both temp tables are 3300 items long. The inner select executes in under a second. All strings are nvarchar(249). All IDs are int. Any ideas? I executed it (it's in a stored proc) for over 12 minutes without it finishing.

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  • Is it a problem if i query again and again to SQL Server 2005 and 2000?

    - by learner
    Window app i am constructing is for very low end machines (Celeron with max 128 RAM). From the following two approaches which one is the best (I don't want that application becomes memory hog for low end machines):- Approach One:- Query the database Select GUID from Table1 where DateTime <= @givendate which is returning me more than 300 thousands records (but only one field i.e. GUID - 300 thousands GUIDs). Now running a loop to achieve next process of this software based on GUID. Second Approach:- Query the database Select Top 1 GUID from Table1 where DateTime <= @givendate with top 1 again and again until all 300 thousands records done. It will return me only one GUID at a time, and I can do my next step of operation. What do you suggest which approach will use the less Memory Resources?? (Speed / performance is not the issue here).

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  • servlet ArrayList and HashMap problem witch result

    - by nonameplum
    Hi, I have that code List<Map<String, Object>> data = new ArrayList<Map<String, Object>>(); Map<String, Object> item = new HashMap<String, Object>(); data.clear(); item.clear(); int i = 0; while (i < 5){    item.put("id", i);    i++;    out.println("id: " + item.get("id"));    out.println("--------------------------");    data.add(item); } for(i=0 ; i<5 ; i++){    out.println("print data[" + i + "]" + data.get(i)); } Result of that is: id: 0 -------------------------- id: 1 -------------------------- id: 2 -------------------------- id: 3 -------------------------- id: 4 -------------------------- print data[0]{id=4} print data[1]{id=4} print data[2]{id=4} print data[3]{id=4} print data[4]{id=4} Why only last element is stored?

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  • Autohotkey to map F5 to Shift+Home and then F5 - eventually executing a single line query in sql server?

    - by puretechy
    Reading the syntax from autohotkey, I am trying to achieve this. But the first step of selecting the entire line is not working:- F5:: send {Shift Home} return I have tried few others too, but its not working. This is not sending Shift+Home combination on pressing F5 key. Please tell me what's wrong with this? Also if possible, what to do next?, as if I will write send {F5} I believe, it will recursively fire this script again and again..

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  • WTF why does this SQL work in VS but not in CODE?

    - by acidzombie24
    The line cmd.ExecuteNonQuery(); cmd.CommandText CREATE TRIGGER subscription_trig_0 ON subscription AFTER INSERT AS UPDATE user_data SET msg_count=msg_count+1 FROM user_data JOIN INSERTED ON user_data.id = INSERTED.recipient; The exception: Incorrect syntax near the keyword 'TRIGGER'. Then using VS 2010, connected to the very same file (a mdf file) i run the query above and i get a success message. WTF!

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  • SQL -- How is DISTINCT so fast without an index?

    - by Jonathan
    Hi, I have a database with a table called 'links' with 600 million rows in it in SQLite. There are 2 columns in the database - a "src" column and a "dest" column. At present there are no indices. There are a fair number of common values between src and dest, but also a fair number of duplicated rows. The first thing I'm trying to do is remove all the duplicate rows, and then perform some additional processing on the results, however I've been encountering some weird issues. Firstly, SELECT * FROM links WHERE src=434923 AND dest=5010182. Now this returns one result fairly quickly and then takes quite a long time to run as I assume it's performing a tablescan on the rest of the 600m rows. However, if I do SELECT DISTINCT * FROM links, then it immediately starts returning rows really quickly. The question is: how is this possible?? Surely for each row, the row must be compared against all of the other rows in the table, but this would require a tablescan of the remaining rows in the table which SHOULD takes ages! Any ideas why SELECT DISTINCT is so much quicker than a standard SELECT?

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  • Building a decision-making game in jQuery? Where would I store data....

    - by redconservatory
    I built a slideshow/decision-making game in Flash but would like to try to redo it using jQuery. The slideshow part seems simple enough, however I have a series of user decisions that I'm not sure how to approach. In flash, if the user makes a decision, I would just store this in a variable or shared local objects, is this the same for jQuery? i.e. mix regular javascript variables with the jQuery?

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  • Why does this SQL work in VS but not in code?

    - by acidzombie24
    The line cmd.ExecuteNonQuery(); cmd.CommandText CREATE TRIGGER subscription_trig_0 ON subscription AFTER INSERT AS UPDATE user_data SET msg_count = msg_count + 1 FROM user_data JOIN INSERTED ON user_data.id = INSERTED.recipient; The exception: Incorrect syntax near the keyword 'TRIGGER'. Then using VS 2010, connected to the very same file (a mdf file) i run the query above and i get a success message.

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  • Are these 2 sql queries equivalent in all respects (e.g. estimated and actual execution plan)?

    - by Xerion
    Are query 1) == 2) in terms of estimated query plan AND actual plan? (can statistics affect the actual plan here, ever?) declare @cat int -- input param from prc ... 1) select * from A as a join B as b on b.id = a.id on b.cat = @cat join C as c on c.fid = b.fid on c.cat = @cat where a.cat = @cat 2) select * from A as a join B as b on b.id = a.id on b.cat = a.cat join C as c on c.fid = b.fid on c.cat = b.cat where a.cat = @cat It seems to me that these should logically be equivalent and the execution plan should always be the same regardless of actual difference in tables. And adding more conditions either in join, or where, or add more tables to join shouldn't change this. Are there cases this is not true?

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  • SQL query select from table and group on other column...

    - by scaryjones
    I'm phrasing the question title poorly as I'm not sure what to call what I'm trying to do but it really should be simple. I've a link / join table with two ID columns. I want to run a check before saving new rows to the table. The user can save attributes through a webpage but I need to check that the same combination doesn't exist before saving it. With one record it's easy as obviously you just check if that attributeId is already in the table, if it is don't allow them to save it again. However, if the user chooses a combination of that attribute and another one then they should be allowed to save it. Here's an image of what I mean: So if a user now tried to save an attribute with ID of 1 it will stop them, but I need it to also stop them if they tried ID's of 1, 10 so long as both 1 and 10 had the same productAttributeId. I'm confusing this in my explanation but I'm hoping the image will clarify what I need to do. This should be simple so I presume I'm missing something.

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  • SQL Server: How to tell if a database is a system database?

    - by Vinko Vrsalovic
    I know that so far (until MSSQL 2005 at least), system databases are master, model, msdb and tempdb. Thing is, as far as I can tell, this is not guaranteed to be preserved in the future. And neither the sys.databases view nor the sys.sysdatabases view tell me if a database is considered as a system database. Is there someplace where this information (whether a database is considered a system database or not) can be obtained?

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  • Sql Server 2000 Stored Procedure Prevents Parallelism or something?

    - by user187305
    I have a huge disgusting stored procedure that wasn't slow a couple months ago, but now is. I barely know what this thing does and I am in no way interested in rewriting it. I do know that if I take the body of the stored procedure and then declare/set the values of the parameters and run it in query analyzer that it runs more than 20x faster. From the internet, I've read that this is probably due to a bad cached query plan. So, I've tried running the sp with "WITH RECOMPILE" after the EXEC and I've also tried putting the "WITH RECOMPLE" inside the sp, but neither of those helped even a little bit. When I look at the execution plan of the sp vs the query, the biggest difference is that the sp has "Parallelism" operations all over the place and the query doesn't have any. Can this be the cause of the difference in speeds? Thank you, any ideas would be great... I'm stuck.

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  • storage classes

    - by ramyabanu
    what is the difference between a variable declared as an auto and static? what is the difference in allocation of memory in auto and static variable? why do we use static with array of pointers and what is its significance?

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  • Is "campaign_$" a bad name for a SQL column?

    - by Summer
    PostgreSQL has allowed me to name a column "campaign_$". I like the name because it's short and to the point, and other potential names like "campaign_receipts" seem longer and less clear. BUT, I wonder if I'll eventually regret putting a $ symbol in a column name, either in PHP or in some other distant part of the architecture. Should I just stick to letters and underscores? Thanks!

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