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  • Database table schema design - varchar(n). Suitable choice of N

    - by morpheous
    Coming from a C background, I may be getting too anal about this and worrying unnecessarily about bits and bytes here. Still, I cant help thinking how the data is actually stored and that if I choose an N which is easily factorizable into a power of 2, the database will be more effecient in how it packs data etc. Using this "logic", I have a string field in a table which is a variable length up to 21 chars. I am tempted to use 32 instead of 21, for the reason given above - however now I am thinking that I am wasting disk space because there will be space allocated for 11 extra chars that are guaranteed to be never used. Since I envisage storing several tens of thousands of rows a day, it all adds up. Question: Mindful of all of the above, Should I declare varchar(21) or varchar(32) and why?

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  • Forcing the use of an index can improve performance?

    - by aF.
    Imagine that we have a query like this: select a.col1, b.col2 from t1 a inner join t2 b on a.col1 = b.col2 where a.col1 = 'abc' Both col1 and col2 don't have any index. If I add another restriction on the where clause, one that is always correct but with a column with an index: select a.col1, b.col2 from t1 a inner join t2 b on a.col1 = b.col2 where a.col1 = 'abc' and a.id >= 0 -- column always true and with index May the query perform faster since it may use the index on id column?

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  • Automatically Persisting a Complex Java Object

    - by VeeArr
    For a project I am working on, I need to persist a number of POJOs to a database. The POJOs class definitions are sometimes highly nested, but they should flatten okay, as the nesting is tree-like and contains no cycles (and the base elements are eventually primitives/Strings). It is preferred that the solution used create one table per data type and that the tables will have one field per primitive member in the POJO. Subclassing and similar problems are not issues for this particular project. Does anybody know of any existing solutions that can: Automatically generate a CREATE TABLE definition from the class definition Automatically generate a query to persist an object to the database, given an instance of the object Automatically generate a query to retrieve an object from the database and return it as a POJO, given a key. Solutions that can do this with minimum modifications/annotions to the class files and minimum external configuration are preferred. Example: Java classes //Class to be persisted class TypeA { String guid; long timestamp; TypeB data1; TypeC data2; } class TypeB { int id; int someData; } class TypeC { int id; int otherData; } Could map to CREATE TABLE TypeA ( guid CHAR(255), timestamp BIGINT, data1_id INT, data1_someData INT, data2_id INt, data2_otherData INT ); Or something similar.

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  • Greatest not null column

    - by Álvaro G. Vicario
    I need to update a row with a formula based on the largest value of two DATETIME columns. I would normally do this: GREATEST(date_one, date_two) However, both columns are allowed to be NULL. I need the greatest date even when the other is NULL (of course, I expect NULL when both are NULL) and GREATEST() returns NULL when one of the columns is NULL. This seems to work: GREATEST(COALESCE(date_one, date_two), COALESCE(date_two, date_one)) But I wonder... am I missing a more straightforward method?

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  • Is this a bad indexing strategy for a table?

    - by llamaoo7
    The table in question is part of a database that a vendor's software uses on our network. The table contains metadata about files. The schema of the table is as follows Metadata ResultID (PK, int, not null) MappedFieldname (char(50), not null) Fieldname (PK, char(50), not null) Fieldvalue (text, null) There is a clustered index on ResultID and Fieldname. This table typically contains millions of rows (in one case, it contains 500 million). The table is populated by 24 workers running 4 threads each when data is being "processed". This results in many non-sequential inserts. Later after processing, more data is inserted into this table by some of our in-house software. The fragmentation for a given table is at least 50%. In the case of the largest table, it is at 90%. We do not have a DBA. I am aware we desperately need a DB maintenance strategy. As far as my background, I'm a college student working part time at this company. My question is this, is a clustered index the best way to go about this? Should another index be considered? Are there any good references for this type and similar ad-hoc DBA tasks?

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  • SQL with codition on calculated value

    - by user619893
    I have a table with products, their amount and their price. I need to select all entries where the average price per article is between a range. My query so far: SELECT productid,AVG(SUM(price)/SUM(amount)) AS avg FROM stock WHERE avg=$from AND avg<=$to GROUP BY productid If do this, it tells me avg doesnt exist. Also i obviously need to group by because the sum and average need to be per wine

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  • PHP, MySQL - would results-array shuffle be quicker than "select... order by rand()"?

    - by sombe
    I've been reading a lot about the disadvantages of using "order by rand" so I don't need update on that. I was thinking, since I only need a limited amount of rows retrieved from the db to be randomized, maybe I should do: $r = $db->query("select * from table limit 500"); for($i;$i<500;$i++) $arr[$i]=mysqli_fetch_assoc($r); shuffle($arr); (i know this only randomizes the 500 first rows, be it). would that be faster than $r = $db->("select * from table order by rand() limit 500"); let me just mention, say the db tables were packed with more than...10,000 rows. why don't you do it yourself?!? - well, i have, but i'm looking for your experienced opinion. thanks!

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  • mysql_fetch_row() not a valid result resource

    - by user1717305
    I am confused, I don't know what's wrong. I'm about to transfer all data from my first table to the other. Here is my code: $getdata = mysql_query("SELECT Quantity, Description, Total FROM ordercart"); while($row = mysql_fetch_row($getdata)) { foreach($row as $cell){ $query1 = mysql_query("INSERT INTO ordermem (Quantity, Description, Total) VALUES ($cell)",$connect); } mysql_free_result($getdata); } I get the error: Warning: mysql_fetch_row(): 5 is not a valid MySQL result resource.

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  • Client to server data upload

    - by RickBowden
    I'm trying to design a system similar to the traditional server monitoring systems like MOM, Tivoli, Open View, where an agent will record data and then upload it to a central database once a day, but them also be able to send immediate alerts back to the server. I'm not sure what the best methodology might be for this. I've started looking at Microsoft sync services but I'm not sure if it will fit my needs. I'm using VS2008 and C#. Does anyone have any experience or ideas about how I should go about this task?

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  • how to get an xml in a variable

    - by sam
    I have a stored procedure that will return xml. I have delared a variable of type xml and trying to execute the following code declare @v xml set @v = execute get_xml @id, 33 whereas id is returned by another query. now it keeps compalinng about the following error Incorrect syntax near the keyword 'execute'.

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  • MS Access PIVOT with User Defined Field

    - by user2535359
    Any of you good souls please help!! I need to query the source table shown in the below. (NULL are blank fields) UNUM, Ticket, Overflow 1 , 135 , NULL 1 , 136 ,NULL 1, 137, NULL 1, 138, NULL 1, NULL, 2b 2, 135, NULL 2, 136, NULL 2, 137, NULL 3, 135, NULL 3, 136, NULL 3, 137,NULL 3, 138, NULL 3, 139, NULL 3, 140, NULL 3, NULL, 66a 4, NULL, 12a 5, NULL, 14a I need to generate the output as shown below. UserNum, Ticket1, Ticket2, Ticket3, Ticket4, Ticket5, Ticket6, Ticket7, Ticket8, Ticket9, Overflow 1, 135, 136, 137, 138, Null, Null, Null, Null, Null, 2b 2, 135, 136, 137, Null, Null, Null, Null, Null, Null, Null 3, 135, 136, 137, 138, 139, 140, Null, Null, Null, 66a 4, Null, Null, Null, Null, Null, Null, Null, Null, Null, 12a 5, Null, Null, Null, Null, Null, Null, Null, Null, Null, 14a The source table has multiple tickets assigned to user. There are always maximum of 9 tickets. The user either has a ticket or an overflow but here can be only overflow per user. I am having issue pivoting the data in Ticket column to pre-defined field names like Ticket1, Ticket2...

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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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  • User activity vs. System activity on the Index Usage Statistics report

    - by Zachary G Jensen
    I recently decided to crawl over the indexes on one of our most heavily used databases to see which were suboptimal. I generated the built-in Index Usage Statistics report from SSMS, and it's showing me a great deal of information that I'm unsure how to understand. I found an article at Carpe Datum about the report, but it doesn't tell me much more than I could assume from the column titles. In particular, the report differentiates between User activity and system activity, and I'm unsure what qualifies as each type of activity. I assume that any query that uses a given index increases the '# of user X' columns. But what increases the system columns? building statistics? Is there anything that depends on the user or role(s) of a user that's running the query?

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  • Multiple/Sub quries with codeigniter

    - by user1011713
    I just started with Codeigniter and this is driving me nuts. I have a query that determines whether a user has bought any programs. I then have to use that program's type category to run and determine how many times he or she has recorded a query in another table. Sorry for the confusion but the code hopefully makes sense. I'm having problem returning the two arrays from my Model to my Controller to onto the view obviously. function specificPrograms() { $specific_sql = $this->db->query("SELECT program,created FROM `assessment` WHERE uid = $this->uid"); if($specific_sql->num_rows() > 0) { foreach ($specific_sql->result() as $specific) { $data[] = $specific; $this->type = $specific->program; } return $data; } $sub_sql = $this->db->query("SELECT id FROM othertable WHERE user_id_fk = $this->uid and type = '$this->type'"); if($sub_sql->num_rows() > 0) { foreach ($sub_sql->result() as $otherp) { $data[] = $otherp; } return $data; } } Then in my Controller I have, $data['specific'] = $this->user_model->specificPrograms(); $data['otherp'] = $this->user_model->specificPrograms(); Thanks for any help.

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  • excel:mysql: rs.Update not working

    - by every_answer_gets_a_point
    i am updating a table using an ODBC connection from excel to mysql unfortunately the only column that gets updated is this one: .Fields("instrument") = "NA" where i am assigning variables to .Fields, it is putting NULL values!! what is going on here? here's the code Option Explicit Dim oConn As ADODB.Connection Private Sub ConnectDB() Set oConn = New ADODB.Connection oConn.Open "DRIVER={MySQL ODBC 5.1 Driver};" & _ "SERVER=localhost;" & _ "DATABASE=employees;" & _ "USER=root;" & _ "PASSWORD=pas;" & _ "Option=3" End Sub Function esc(txt As String) esc = Trim(Replace(txt, "'", "\'")) End Function Private Sub InsertData() Dim dpath, atime, rtime, lcalib, aname, rname, bstate, instrument As String Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset ConnectDB With wsBooks rs.Open "batchinfo", oConn, adOpenKeyset, adLockOptimistic, adCmdTable Worksheets.Item("Report 1").Select dpath = Trim(Range("B2").Text) atime = Trim(Range("B3").Text) rtime = Trim(Range("B4").Text) lcalib = Trim(Range("B5").Text) aname = Trim(Range("B6").Text) rname = Trim(Range("B7").Text) bstate = Trim(Range("B8").Text) ' instrument = GetInstrFromXML(wbBook.FullName) With rs .AddNew ' create a new record ' add values to each field in the record .Fields("datapath") = dpath .Fields("analysistime") = atime .Fields("reporttime") = rtime .Fields("lastcalib") = lcalib .Fields("analystname") = aname .Fields("reportname") = rname .Fields("batchstate") = bstate .Fields("instrument") = "NA" .Update ' stores the new record End With ' get the last id Set rs = oConn.Execute("SELECT @@identity", , adCmdText) 'MsgBox capture_id rs.Close Set rs = Nothing End With End Sub

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  • simple query Delete records in a table based on count logic

    - by user1905941
    a table with a pk and status column which is having values as 'Y','N','NULL' Query: get the count of records with status column as 'Y', if this count exceeds 1% of total count of records then dont delete , else delete the records in the table. i tried like this Declare v_count Number; v_count1 Number; BEGIN v_count := select count(*) from temp; v_count1 := select count(*) from temp where status = 'Y' ; v_count := v_count + ((0.1) * (v_count)) if (v_count1 > v_count) { insert into temp1 values(pk,status) } else { Delete from temp ; } END;

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  • How can I find days between different paired rows?

    - by Anthony
    I've been racking my brain about how to do this in one query without PHP code. In a nutshell, I have a table that records email activity. For the sake of this example, here is the data: recipient_id activity date 1 delivered 2011-08-30 1 open 2011-08-31 2 delivered 2011-08-30 3 delivered 2011-08-24 3 open 2011-08-30 3 open 2011-08-31 The goal: I want to display to users a single number that tells how many recipients open their email within 24 hours. E.G. "Users that open their email within 24 hours: 13 Readers" In the case of the sample data, above, the value would be "1". (Recipient one was delivered an email and opened it the next day. Recipient 2 never opened it and recipient 3 waited 5 days.) Can anyone think of a way to express the goal in a single query? Reminder: In order to count, the person must have a 'delivered' tag and at least one 'open' tag. Each 'open' tag only counts once per recipient.

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  • Notification 7 Days Before Payment PHP No Error Message

    - by user1858672
    So I have PHP script running on cron daily. It is suppose to check the date and send an email if it is 7 days before any payments as a reminder. I haven't used PHP in a long time so sorry if the way I did it was ridiculous or something. Thanks a lot. I would say what the problem is but I don't get any error message or anything.. <?php mysqli_connect("xxxxxx", "xxxxxxx", "xxxxxxxxx") or die(mysqli_error()); mysqli_select_db("xxxxxxxxx") or die(mysqli_error()); //Retrieve original payment dates and enter them into an array $result = mysqli_query("SELECT DateCreated FROM UserTable"); $payment_dates = mysqli_fetch_array($result); //Puts original payment date into month-day format $md_payment_dates = substr($payment_dates, 5); //Gets todays date in m-d format and adds 7 days to it $due_date = mktime(0, 0, 0, date("m"), date("d")+7); //Checks if any payment days match today's date. If there are none it script will stop. if (count(preg_grep($due_date, $md_payment_dates)) > 0) { //Retrieves usernames of users that have an invoice due. $users_to_pay = mysqli_fetch_array("SELECT Username IN UserTable WHERE DateCreated = $date"); //Notifies you via email $to = "[email protected]"; $subject = "7 Day Payment Reminder"; $message = "Hi, <br /> The following owe a payment in 7 days : " + $users_to_pay ".<br/> Their payments are due on " + $md_payment_dates " of this year."; mail($to, $subject, $message); exit(); }else{ exit(); } ?>

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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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  • Search by nvarchar

    - by ziks
    Hi all. I have this problem. In table I have column which is nvarcar type. and row in this column is row1= 1;6 row2 = 12 row3 =6;5;67 etc... I try to search this column. for example when i send 1 i try to get only row1. I use LIKE but in result set I get row1 and row2. How can I achieved this, any help is appreciated. Tnx...

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