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  • Does the order of columns matter in a group by clause?

    - by Jeff Meatball Yang
    If I have two columns, one with very high cardinality and one with very low cardinality (unique # of values), does it matter in which order I group by? Here's an example: select dimensionName, dimensionCategory, sum(someFact) from SomeFact f join SomeDim d on f.dimensionKey = d.dimensionKey group by d.dimensionName, -- large number of unique values d.dimensionCategory -- small number of unique values Are there situations where it matters?

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  • any practices ,samples for ERD?

    - by just_name
    Q: I wanna any web sites , any books just for training on ERD and normalization ,, i wanna a lot of samples ,practices,and case studies with recommended answers, to strength myself in database design.and avoid the poor data base design i made . note:i don't need books to explain the concepts , what i need is practices ,examples,case studies with recommended answers. Thanks in advance.

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  • COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better?

    - by zneak
    Hello guys, I often find these three variants: SELECT COUNT(*) FROM Foo; SELECT COUNT(1) FROM Foo; SELECT COUNT(PrimaryKey) FROM Foo; As far as I can see, they all do the same thing, and I find myself using the three in my codebase. However, I don't like to do the same thing different ways. To which one should I stick? Is any one of them better than the two others?

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  • Thinking of an Inner Join as a Cross Join and then satisfying some condition(s)?

    - by Jian Lin
    It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then satisfying some condition(s)? Because the equi-join can be obvious, but the non-equi-join can be a bit confusing. But if we always use the Cross Join, and then filter out the ones satisfying the condition, then we get the resulting table. In other words, we can always analyze it by using the first record on the left table, and then go through every single records on the right, and then repeat that for 2nd record on the left, and for the 3rd, 4th, ... etc. So in our mind, we can analyze it using this way, and it is like O(n^2), although what happens in the DBMS maybe that it is a lot faster (when an index is present). Is there another good way to think of it besides this method?

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  • How to get top 3 frequencies in MySQL?

    - by Amenhotep
    Hello, In MySQL I have a table called "meanings" with three columns: "person" (int), "word" (byte, 16 possible values) "meaning" (byte, 26 possible values). A person assigns one or more meanings to each word: person word meaning ------------------- 1 1 4 1 2 19 1 2 7 <-- second meaning for word 2 1 3 5 ... 1 16 2 Then another person, and so on. There will be thousands of persons. I need to find for each of the 16 words the top three meanings (with their frequencies). Something like: word 1: meaning 5 (35% of people), meaning 19 (22% of people), meaning 2 (13% of people) word 2: meaning 8 (57%), meaning 1 (18%), meaning 22 (7%) ... Is it possible to solve this with a single MySQL query? (If this problem is a classic one and has been answered elsewhere, I would appreciate if you could give me a link to the solution.) Thank you very much, ve

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  • What's wrong with this SQL query?

    - by ThinkingInBits
    I have two tables: photographs, and photograph_tags. Photograph_tags contains a column called photograph_id (id in photographs). You can have many tags for one photograph. I have a photograph row related to three tags: boy, stream, and water. However, running the following query returns 0 rows SELECT p.* FROM photographs p, photograph_tags c WHERE c.photograph_id = p.id AND (c.value IN ('dog', 'water', 'stream')) GROUP BY p.id HAVING COUNT( p.id )=3 Is something wrong with this query?

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  • Tool Compare the tables in two different databeses

    - by user191124
    I am using Toad. Frequently i need to compare tables in two different test environments. the tables present in them are same but the data differs. i just need to know what are the differences in the same tables which are in two different data bases.Are there any tools which can be installed on windows and use it to compare. Much appreciate your help:)

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  • Lock Question - When is an Update (U) lock issued?

    - by Randy Minder
    We are trying to resolve a deadlock problem. The transaction that is getting rolled back is attempting to issue an Update (U) lock on a resource that another transaction has an Exclusive (X) lock on. According to Books Online (http://msdn.microsoft.com/en-us/library/ms175519.aspx), an Update lock is supposed to prevent deadlocks, not cause them. So, my question is, why/when is an Update lock applied to a resource? We're a little confused about this because the resource that is attempting to have the Update lock applied to will not be updated by the process that is having the transaction rolled back. Thanks for your help on this. Randy

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  • How can i get rid of 'ORA-01489: result of string concatenation is too long' in this query?

    - by core_pro
    this query gets the dominating sets in a network. so for example given a network A<----->B B<----->C B<----->D C<----->E D<----->C D<----->E F<----->E it returns B,E B,F A,E but it doesn't work for large data because i'm using string methods in my result. i have been trying to remove the string methods and return a view or something but to no avail With t as (select 'A' as per1, 'B' as per2 from dual union all select 'B','C' from dual union all select 'B','D' from dual union all select 'C','B' from dual union all select 'C','E' from dual union all select 'D','C' from dual union all select 'D','E' from dual union all select 'E','C' from dual union all select 'E','D' from dual union all select 'F','E' from dual) ,t2 as (select distinct least(per1, per2) as per1, greatest(per1, per2) as per2 from t union select distinct greatest(per1, per2) as per1, least(per1, per2) as per1 from t) ,t3 as (select per1, per2, row_number() over (partition by per1 order by per2) as rn from t2) ,people as (select per, row_number() over (order by per) rn from (select distinct per1 as per from t union select distinct per2 from t) ) ,comb as (select sys_connect_by_path(per,',')||',' as p from people connect by rn > prior rn ) ,find as (select p, per2, count(*) over (partition by p) as cnt from ( select distinct comb.p, t3.per2 from comb, t3 where instr(comb.p, ','||t3.per1||',') > 0 or instr(comb.p, ','||t3.per2||',') > 0 ) ) ,rnk as (select p, rank() over (order by length(p)) as rnk from find where cnt = (select count(*) from people) order by rnk ) select distinct trim(',' from p) as p from rnk where rnk.rnk = 1`

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  • Loading Fact Table + Lookup / UnionAll for SK lookups.

    - by Nev_Rahd
    I got to populate FactTable with 12 lookups to dimension table to get SK's, of which 6 are to different Dim Tables and rest 6 are lookup to same DimTable (type II) doing lookup to same natural key. Ex: PrimeObjectID = lookup to DimObject.ObjectID = get ObjectSK and got other columns which does same OtherObjectID1 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID2 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID3 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID4 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID5 = lookup to DimObject.ObjectID = get ObjectSK for such multiple lookup how should go in my SSIS package. for now am using lookup / unionall foreach lookup. Is there a better way to this.

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  • Using 'in' in Join

    - by Ruslan
    i have two selects a & b and i join them like: select * from ( select n.id_b || ',' || s.id_b ids, n.name, s.surname from names n, surnames s where n.id_a = s.id_a ) a left join ( select sn.id, sn.second_name ) b on b.id in (a.ids) in this case join doesn't work :( The problem is in b.id in (a.ids). But why if it looks like 12 in (12,24) and no result :(

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  • C# Tupel group limitation

    - by user609511
    How can i controll the loop of Tupel Repeatation ? Someone has give me a hint about my algorithm. I modified a little bit his algorithm. int LimCol = Convert.ToInt32(LimitColis); result = oListTUP .GroupBy(x => x.Item1) .Select(g => new { Key = g.Key, Sum = g.Sum(x => x.Item2), Poids = g.Sum(x => x.Item3), }) .Select(p => new { Key = p.Key, Items = Enumerable.Repeat(LimCol , p.Sum / LimCol).Concat(Enumerable.Repeat(p.Sum % LimCol, 1)), CalculPoids = p.Poids / (Enumerable.Repeat(LimCol, p.Sum / LimCol).Concat(Enumerable.Repeat(p.Sum % LimCol, 1))).Count() }) .SelectMany(p => p.Items.Select(i => Tuple.Create(p.Key, i, p.CalculPoids))) .ToList(); foreach (var oItem in result) { Label1.Text += oItem.Item1 + "--" + oItem.Item2 + "--" + oItem.Item3 + "<br>"; } the result with LimCol = 3 as you can see i colored with red is the problem. i expected: 0452632--3--3,75 0452632--3--3,75 0452632--3--3,75 0452632--3--3,75 essai 49--3--79,00 essai 49--2--79,00 Thanks you in advance

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  • IDENTITY_INSERT is set to off error

    - by kingrichard2005
    I have a MVC web application with a table in the model that I would like to add to. I have the primary key set along with the other data fields, but every time I try to add to the table, I get the following error: "Cannot insert explicit value for identity column in table 'TABLE_NAME' when IDENTITY_INSERT is set to OFF." I'm not sure why this problem is coming up, I have the primary key set as the identity and it is also set to auto increment in the Visual Studio table designer. Is there any way I can adjust the IDENTITY_INSERT parameter in the table designer in Visual Studio?? Or is there some other issue that might be causing this.

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  • Postgre database ignoring created index ?!

    - by drasto
    I have an Postgre database and a table called my_table. There are 4 columns in that table (id, column1, column2, column3). The id column is primary key, there are no other constrains or indexes on columns. The table has about 200000 rows. I want to print out all rows which has value of column column2 equal(case insensitive) to 'value12'. I use this: SELECT * FROM my_table WHERE column2 = lower('value12') here is the execution plan for this statement(result of set enable_seqscan=on; EXPLAIN SELECT * FROM my_table WHERE column2 = lower('value12')): Seq Scan on my_table (cost=0.00..4676.00 rows=10000 width=55) Filter: ((column2)::text = 'value12'::text) I consider this to be to slow so I create an index on column column2 for better prerformance of searches: CREATE INDEX my_index ON my_table (lower(column2)) Now I ran the same select: SELECT * FROM my_table WHERE column2 = lower('value12') and I expect it to be much faster because it can use index. However it is not faster, it is as slow as before. So I check the execution plan and it is the same as before(see above). So it still uses sequential scen and it ignores the index! Where is the problem ?

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  • Passing in a lambda to a Where statement

    - by sonicblis
    I noticed today that if I do this: var items = context.items.Where(i => i.Property < 2); items = items.Where(i => i.Property > 4); Once I access the items var, it executes only the first line as the data call and then does the second call in memory. However, if I do this: var items = context.items.Where(i => i.Property < 2).Where(i => i.Property > 4); I get only one expression executed against the context that includes both where statements. I have a host of variables that I want to use to build the expression for the linq lambda, but their presence or absence changes the expression such that I'd have to have a rediculous number of conditionals to satisfy all cases. I thought I could just add the Where() statements as in my first example above, but that doesn't end up in a single expression that contains all of the criteria. Therefore, I'm trying to create just the lambda itself as such: //bogus syntax if (var1 == "something") var expression = Expression<Func<item, bool>>(i => i.Property == "Something); if (var2 == "somethingElse") expression = expression.Where(i => i.Property2 == "SomethingElse"); And then pass that in to the where of my context.Items to evaluate. A) is this right, and B) if so, how do you do it?

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  • Advanced LINQ Update Statement

    - by user1902490
    I have a data base with Price_old like: Date --- Hour --- Price _____________________________ Jan 1 --- 1 --- $3.0 Jan 1 --- 2 --- $3.1 Jan 1 --- 3 --- $3.3 Jan 1 --- 4 --- $3.15 Jan 2 --- 1 --- $2.95 Jan 2 --- 2 --- $3.2 Jan 2 --- 3 --- $3.05 What I then have is a spreadsheet, with the same structure, that I will be reading into a datatable, I'll call the new datatable Price_New, note that price new may not have all the same date/hours as Price_Old So, I end up with 2 datatables, Price_Old, and Price_New, and what I need to do is update Price_old with the new prices in Price_New, and then commit those new prices to the Database. I am kinda new to LINQ (about 30 mins of experience) and would really appreciate if someone could give me a pointer or two on whether or not this is doing in LINQ and what the best method would be. Thanks

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  • rookie MySql question about paging; Is one query enough?

    - by Camran
    I have managed to get paging to work, almost. I want to display to the user, total nr of records found, and the currently displayed records. Ex: 4000 found, displaying 0-100. I am testing this with the nr 2 (because I don't have that many records, have like 20). So I am using LIMIT $start, $nr_results; Do I have to make two queries in order to display the results the way I want, one query fetching all records and then make a mysql_num_rows to get all records, then the one with the LIMIT ? I have this: mysql_num_rows($qry_result); $total_pages = ceil($num_total / $res_per_page); //$res_per_page==2 and $num_total = 2 if ($p - 10 < 1) { $pagemin=1; } else { $pagemin = $p - 10; } if ($p + 10 $total_pages) { $pagemax = $total_pages; } else { $pagemax = $p + 10; } Here is the query: SELECT mt.*, fordon.*, boende.*, elektronik.*, business.*, hem_inredning.*, hobby.* FROM classified mt LEFT JOIN fordon ON fordon.classified_id = mt.classified_id LEFT JOIN boende ON boende.classified_id = mt.classified_id LEFT JOIN elektronik ON elektronik.classified_id = mt.classified_id LEFT JOIN business ON business.classified_id = mt.classified_id LEFT JOIN hem_inredning ON hem_inredning.classified_id = mt.classified_id LEFT JOIN hobby ON hobby.classified_id = mt.classified_id ORDER BY modify_date DESC LIMIT 0, 2 Thanks, if you need more input let me know. Basically Q is, do I have to make two queries?

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  • Oracle SQL CMD Line!!!

    - by DAVID
    Hi when ever perform select statements in the command line tool it doesnt use all of the space.. ive modified buffer size and window size and it just doesnt work. here is the Screenshot http://img19.imageshack.us/img19/8954/cmdoracle.jpg

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  • Why does this MySQL function return null?

    - by Shore
    Description: the query actually run have 4 results returned,as can be see from below, what I did is just concate the items then return, but unexpectedly,it's null. I think the code is self-explanatory: DELIMITER | DROP FUNCTION IF EXISTS get_idiscussion_ask| CREATE FUNCTION get_idiscussion_ask(iask_id INT UNSIGNED) RETURNS TEXT DETERMINISTIC BEGIN DECLARE done INT DEFAULT 0; DECLARE body varchar(600); DECLARE created DATETIME; DECLARE anonymous TINYINT(1); DECLARE screen_name varchar(64); DECLARE result TEXT; DECLARE cur1 CURSOR FOR SELECT body,created,anonymous,screen_name from idiscussion left join users on idiscussion.uid=users.id where idiscussion.iask_id=iask_id; DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1; SET result = ''; OPEN cur1; REPEAT FETCH cur1 INTO body, created, anonymous, screen_name; SET result = CONCAT(result,'<comment><body><![CDATA[',body,']]></body>','<replier>',if(screen_name is not null and !anonymous,screen_name,''),'</replier>','<created>',created,'</created></comment>'); UNTIL done END REPEAT; CLOSE cur1; RETURN result; END | DELIMITER ; mysql> DELIMITER ; mysql> select get_idiscussion_ask(1); +------------------------+ | get_idiscussion_ask(1) | +------------------------+ | NULL | +------------------------+ 1 row in set (0.01 sec) mysql> SELECT body,created,anonymous,screen_name from idiscussion left join users on idiscussion.uid=users.id where idiscussion.iask_id=1; +------+---------------------+-----------+-------------+ | body | created | anonymous | screen_name | +------+---------------------+-----------+-------------+ | haha | 2009-05-27 04:57:51 | 0 | NULL | | haha | 2009-05-27 04:57:52 | 0 | NULL | | haha | 2009-05-27 04:57:52 | 0 | NULL | | haha | 2009-05-27 04:57:53 | 0 | NULL | +------+---------------------+-----------+-------------+ 4 rows in set (0.00 sec) For those who don't think the code is self-explanatory: Why the function returns NULL?

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  • MySQL: Column Contains Word From List of Words

    - by mellowsoon
    I have a list of words. Lets say they are 'Apple', 'Orange', and 'Pear'. I have rows in the database like this: ------------------------------------------------ |author_id | content | ------------------------------------------------ | 54 | I ate an apple for breakfast. | | 63 | Going to the store. | | 12 | Should I wear the orange shirt? | ------------------------------------------------ I'm looking for a query on an InnoDB table that will return the 1st and 3rd row, because the content column contains one or more words from my list. I know I could query the table once for each word in my list, and use LIKE and the % wildcard character, but I'm wondering if there is a single query method for such a thing?

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  • ASP.Net Gridview paging, pageindex always == 0.

    - by David Archer
    Hi all, Having a slight problem with my ASP.Net 3.5 app. I'm trying to get the program to pick up what page number has been clicked. I'm using ASP.Net's built in AllowPaging="True" function. It's never the same without code, so here it is: ASP.Net: <asp:GridView ID="GridView1" runat="server" CellPadding="4" ForeColor="#333333" GridLines="Vertical" Width="960px" AllowSorting="True" EnableSortingAndPagingCallbacks="True" AllowPaging="True" PageSize="25" > <RowStyle BackColor="#F7F6F3" ForeColor="#333333" /> <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" /> <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" /> <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" /> <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" /> <EditRowStyle BackColor="#999999" /> <AlternatingRowStyle BackColor="White" ForeColor="#284775" /> </asp:GridView> C#: var fillTable = from ft in db.IncidentDatas where ft.pUserID == Convert.ToInt32(ClientList.SelectedValue.ToString()) select new { Reference = ft.pRef.ToString(), Date = ft.pIncidentDateTime.Value.Date.ToShortDateString(), Time = ft.pIncidentDateTime.Value.TimeOfDay, Premesis = ft.pPremises.ToString(), Latitude = ft.pLat.ToString(), Longitude = ft.pLong.ToString() }; if (fillTable.Count() > 0) { GridView1.DataSource = fillTable; GridView1.DataBind(); var IncidentDetails = fillTable.ToList(); for (int i = 0; i < IncidentDetails.Count(); i++) { int pageno = GridView1.PageIndex; int pagenostart = pageno * 25; if (i >= pagenostart && i < (pagenostart + 25)) { //Processing } } } Any idea why GridView1.PageIndex is always = 0? The thing is, the processing works correctly for the grid view.... it will always go to the correct paging page, but it's always 0 when I try to get the number. Help!

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