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  • Mysql random rows

    - by n00b
    please read the whole question... 90% of you dont seem to do that and some of you only read the title obviously... and if you dont know the solution, dont answer - i wont have to downvote you -.-'' im entertaining the idea of getting random rows directly from mysql. what i found was SELECT * FROM tablename WHERE somefield='something' ORDER BY RAND() LIMIT 5 but even i see how slow that would be.. is the only way to do this doing something like SELECT * FROM tablename WHERE somefield='something' LIMIT RAND(aincrementvalue-5), 1 5 times? or is there a way that i with my little knowlege of databases cant come up with ? (no i dont want random indexes. i hate the idea of them...) @commenters - please first look, then think, then look again, think again and then post. i wont point fingers but i dislike stupid comments and why i think random indexes are a nasty hack ? it doesnt give you random results. it gives you x results from a random index in a predefined order its like a gapless id only in the wrong order if you fetch by 1 row and get true randomness you fall back to my method but with an additional junk field finally the reason the field exists is only to serve as a helper to something that can be done without it with almost same performance (but the quality (randomness) is better), so it is a nasty hack ;) i solved it, look @ my answer... if you think its incorrect please tell me :)

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  • Merge computed data from two tables back into one of them

    - by Tyler McHenry
    I have the following situation (as a reduced example). Two tables, Measures1 and Measures2, each of which store an ID, a Weight in grams, and optionally a Volume in fluid onces. (In reality, Measures1 has a good deal of other data that is irrelevant here) Contents of Measures1: +----+----------+--------+ | ID | Weight | Volume | +----+----------+--------+ | 1 | 100.0000 | NULL | | 2 | 200.0000 | NULL | | 3 | 150.0000 | NULL | | 4 | 325.0000 | NULL | +----+----------+--------+ Contents of Measures2: +----+----------+----------+ | ID | Weight | Volume | +----+----------+----------+ | 1 | 75.0000 | 10.0000 | | 2 | 400.0000 | 64.0000 | | 3 | 100.0000 | 22.0000 | | 4 | 500.0000 | 100.0000 | +----+----------+----------+ These tables describe equivalent weights and volumes of a substance. E.g. 10 fluid ounces of substance 1 weighs 75 grams. The IDs are related: ID 1 in Measures1 is the same substance as ID 1 in Measures2. What I want to do is fill in the NULL volumes in Measures1 using the information in Measures2, but keeping the weights from Measures1 (then, ultimately, I can drop the Measures2 table, as it will be redundant). For the sake of simplicity, assume that all volumes in Measures1 are NULL and all volumes in Measures2 are not. I can compute the volumes I want to fill in with the following query: SELECT Measures1.ID, Measures1.Weight, (Measures2.Volume * (Measures1.Weight / Measures2.Weight)) AS DesiredVolume FROM Measures1 JOIN Measures2 ON Measures1.ID = Measures2.ID; Producing: +----+----------+-----------------+ | ID | Weight | DesiredVolume | +----+----------+-----------------+ | 4 | 325.0000 | 65.000000000000 | | 3 | 150.0000 | 33.000000000000 | | 2 | 200.0000 | 32.000000000000 | | 1 | 100.0000 | 13.333333333333 | +----+----------+-----------------+ But I am at a loss for how to actually insert these computed values into the Measures1 table. Preferably, I would like to be able to do it with a single query, rather than writing a script or stored procedure that iterates through every ID in Measures1. But even then I am worried that this might not be possible because the MySQL documentation says that you can't use a table in an UPDATE query and a SELECT subquery at the same time, and I think any solution would need to do that. I know that one workaround might be to create a new table with the results of the above query (also selecting all of the other non-Volume fields in Measures1) and then drop both tables and replace Measures1 with the newly-created table, but I was wondering if there was any better way to do it that I am missing.

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  • NoSQL for filesystem storage organization and replication?

    - by wheaties
    We've been discussing design of a data warehouse strategy within our group for meeting testing, reproducibility, and data syncing requirements. One of the suggested ideas is to adapt a NoSQL approach using an existing tool rather than try to re-implement a whole lot of the same on a file system. I don't know if a NoSQL approach is even the best approach to what we're trying to accomplish but perhaps if I describe what we need/want you all can help. Most of our files are large, 50+ Gig in size, held in a proprietary, third-party format. We need to be able to access each file by a name/date/source/time/artifact combination. Essentially a key-value pair style look-up. When we query for a file, we don't want to have to load all of it into memory. They're really too large and would swamp our server. We want to be able to somehow get a reference to the file and then use a proprietary, third-party API to ingest portions of it. We want to easily add, remove, and export files from storage. We'd like to set up automatic file replication between two servers (we can write a script for this.) That is, sync the contents of one server with another. We don't need a distributed system where it only appears as if we have one server. We'd like complete replication. We also have other smaller files that have a tree type relationship with the Big files. One file's content will point to the next and so on, and so on. It's not a "spoked wheel," it's a full blown tree. We'd prefer a Python, C or C++ API to work with a system like this but most of us are experienced with a variety of languages. We don't mind as long as it works, gets the job done, and saves us time. What you think? Is there something out there like this?

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  • openquery giving differnt results

    - by Mithil Deshmukh
    I have 2 similar queries select * from openquery(powerschool, 'select * from TEACHERS where teachernumber is not null and schoolid=''1050'' and teacherloginid is not null order by teachernumber') and SELECT * from openquery(powerschool, 'SELECT NVL(teachernumber,'''') from TEACHERS where teachernumber is not null and schoolid=''1050'' and teacherloginid is not null order by teachernumber') The first one is giving me 182 rows while the second one gives me 83. What's wrong with the queries?

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  • Check value at insert

    - by ThreeFingerMark
    Hello, i have this three tables. Table: Item Columns: ItemID, Title, Content, NoChange (Date) Table: Tag Columns: TagID, Title Table: ItemTag Columns: ItemID, TagID In the Item Table is a Field with NoChange, if this field = true no Tag is allowed to insert a ItemTag value with this ItemID. How can i check this in the insert? For Updates i have this Statement: UPDATE ItemTag SET TagID = ? where ItemID = ? AND TagID = ? AND exists ( select ItemID from Item where ItemID = ? AND NoChange is null)"); Thank you.

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  • How can I do more than one level of cascading deletes in Linq?

    - by Gary McGill
    If I have a Customers table linked to an Orders table, and I want to delete a customer and its corresponding orders, then I can do: dataContext.Orders.DeleteAllOnSubmit(customer.Orders); dataContext.Customers.DeleteOnSubmit(customer); ...which is great. However, what if I also have an OrderItems table, and I want to delete the order items for each of the orders deleted? I can see how I could use DeleteAllOnSubmit to cause the deletion of all the order items for a single order, but how can I do it for all the orders?

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  • Reuse select query in a procedure in Oracle

    - by Jer
    How would I store the result of a select statement so I can reuse the results with an in clause for other queries? Here's some pseudo code: declare ids <type?>; begin ids := select id from table_with_ids; select * from table1 where id in (ids); select * from table2 where id in (ids); end; ... or will the optimizer do this for me if I simply put the sub-query in both select statements?

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  • Alternative to NOT EXISTS

    - by Dave Colwell
    Hi all, I have two tables linked by an ID column, lets call them Table A and table B. My goal is to find all the records in table A that have no record in table B. For instance: Table A: ID----Value 1-----value1 2-----value2 3-----value3 4-----value4 Table B ID----Value 1-----x 2-----y 4-----z 4-----l As you can see, record with ID = 3 does not exist in table B, so i want a query that will give me record 3 from table A. the way i am currently doing this is by saying AND NOT EXISTS (SELECT ID FROM TableB) but since the tables are huge, the performance on this is terrible. Also, when i tried using a Left Join where TableB.ID is null, it didnt work. Can anyone suggest an alternative?

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  • How to increase query speed without using full-text search?

    - by andre matos
    This is my simple query; By searching selectnothing I'm sure I'll have no hits. SELECT nome_t FROM myTable WHERE nome_t ILIKE '%selectnothing%'; This is the EXPLAIN ANALYZE VERBOSE Seq Scan on myTable (cost=0.00..15259.04 rows=37 width=29) (actual time=2153.061..2153.061 rows=0 loops=1) Output: nome_t Filter: (nome_t ~~* '%selectnothing%'::text) Total runtime: 2153.116 ms myTable has around 350k rows and the table definition is something like: CREATE TABLE myTable ( nome_t text NOT NULL, ) I have an index on nome_t as stated below: CREATE INDEX idx_m_nome_t ON myTable USING btree (nome_t); Although this is clearly a good candidate for Fulltext search I would like to rule that option out for now. This query is meant to be run from a web application and currently it's taking around 2 seconds which is obviously too much; Is there anything I can do, like using other index methods, to improve the speed of this query?

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  • Getting a linq table to be dynamically sent to a method

    - by Damian Spaulding
    I have a procedure: var Edit = (from R in Linq.Products where R.ID == RecordID select R).Single(); That I would like to make "Linq.Products" Dynamic. Something like: protected void Page_Load(object sender, EventArgs e) { something(Linq.Products); } public void something(Object MyObject) { System.Data.Linq.Table<Product> Dynamic = (System.Data.Linq.Table<Product>)MyObject; var Edit = (from R in Dynamic where R.ID == RecordID select R).Single(); My problem is that I my "something" method will not be able to know what table has been sent to it. so the static line: System.Data.Linq.Table Dynamic = (System.Data.Linq.Table)MyObject; Would have to reflect somthing like: System.Data.Linq.Table Dynamic = (System.Data.Linq.Table)MyObject; With being a dynamic catch all variable so that Linq can just execute the code just like I hand coded it statically. I have been pulling my hair out with this one. Please help.

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  • How to apply GROUP_CONCAT in mysql Query

    - by Query Master
    How to apply GROUP_CONCAT in this Query if you guys have any idea or any alternate solution about this please share me. Helps are definitely appreciated also (see Query or result required) Query SELECT WEEK(cpd.added_date) AS week_no,COUNT(cpd.result) AS death_count FROM cron_players_data cpd WHERE cpd.player_id = 81 AND cpd.result = 2 AND cpd.status = 1 GROUP BY WEEK(cpd.added_date); Query output result screen Result Required 23,24,25 AS week_no 2,3,1 AS death_count

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  • how to increase the limit of exceptions in oracle

    - by Arunachalam
    how to increase the limit of exceptions in oracle ? i have a excel sheet in which their are about 900 records to be appended .so i converted the excel to dat file and wrote a batch file that read from the dat file and appends it to the concern table but the batch file stop execution once the exceptions reach 51(all integrity constrain parent key not found) so the remaining valid files are not updated .its very difficult to find which record has integrity constrain is there a way to increase this exception limit ?

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  • Can somebody suggest good source for IMS?

    - by Raja Reddy
    I would like to learn working with IMS, can somebody suggest me a good source? I'm not sure if it matters to say that I have quite good exposure and experience with INSYNC DB2 and QMF. So anything that can depict and explain the advantages and disadvantages over IMS would be really helpful. Thanks for your help beforehand..

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  • MySQL Table structure of thumb UP & DOWN for comments system ?

    - by Axel
    Hello, i already created a table for comments but i want to add the feature of thumb Up and Down for comments like Digg and Youtube, i use php & mysql and i'm wondering What's the best table scheme to implement that so comments with many likes will be on the top. This is my current comments table : comments(id,user,article,comment,stamp) Note: Only registred will be able to vote, so there isn't need to restrict the votes by IP Thanks

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  • Which will be the best query OR there is an another one?

    - by serhan
    SELECT k.id,k.adsoyad, COUNT(DISTINCT(e.id)) as iletisimbilgisisay, COUNT(DISTINCT(f.id)) AS ilangonderensay, COUNT(DISTINCT(g.id)) AS emlaksahibisay, isNULL(MAX(eb.yonetici_kisi),0) AS yoneticiid FROM dbo.kisiler k LEFT OUTER JOIN dbo.emlaklar e ON e.iletisimbilgisi=k.id LEFT OUTER JOIN dbo.emlaklar f ON f.ilangonderen=k.id LEFT OUTER JOIN dbo.emlaklar g ON g.emlaksahibi=k.id LEFT OUTER JOIN dbo.emlakcibilgileri eb ON eb.yonetici_kisi=k.id GROUP BY k.id,k.adsoyad ORDER BY yoneticiid DESC, iletisimbilgisisay DESC, ilangonderensay DESC total execution time (above) 28 SELECT id,adsoyad, (select COUNT(id) FROM dbo.emlaklar WHERE iletisimbilgisi=k.id) AS iletisimbilgisisay, (select COUNT(id) FROM dbo.emlaklar WHERE emlaksahibi=k.id) AS emlaksahibisay, (select COUNT(id) FROM dbo.emlaklar WHERE ilangonderen=k.id) AS ilangonderensay, (Select isNULL(MAX(id),0) FROM dbo.emlakcibilgileri WHERE yonetici_kisi=k.id) AS yoneticiid FROM dbo.kisiler k total execution time 4 my tables are emlaklar: id int, ilangonderen int,iletisimbilgisi int,emlaksahibi int kisiler: id int,kisiadi emlakcibilgileri: id int,yonetici_kisi int,firma and ilangonderen,iletisimbilgisi,emlaksahibi,yonetici_kisi => kisiler.id

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  • sp_help with wildcards

    - by serhio
    There is a command in SqlServer sp_help 'table_name' (table_name or other stuff) Is there a possibility to use it when you don't know the whole table name, with wildcards or something like this: sp_help admin_%

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  • What are the rules governing how a bind variable can be used in Postgres and where is this defined?

    - by Craig Miles
    I can have a table and function defined as: CREATE TABLE mytable ( mycol integer ); INSERT INTO mytable VALUES (1); CREATE OR REPLACE FUNCTION myfunction (l_myvar integer) RETURNS mytable AS $$ DECLARE l_myrow mytable; BEGIN SELECT * INTO l_myrow FROM mytable WHERE mycol = l_myvar; RETURN l_myrow; END; $$ LANGUAGE plpgsql; In this case l_myvar acts as a bind variable for the value passed when I call: SELECT * FROM myfunction(1); and returns the row where mycol = 1 If I redefine the function as: CREATE OR REPLACE FUNCTION myfunction (l_myvar integer) RETURNS mytable AS $$ DECLARE l_myrow mytable; BEGIN SELECT * INTO l_myrow FROM mytable WHERE mycol IN (l_myvar); RETURN l_myrow; END; $$ LANGUAGE plpgsql; SELECT * FROM myfunction(1); still returns the row where mycol = 1 However, if I now change the function definition to allow me to pass an integer array and try to this array in the IN clause, I get an error: CREATE OR REPLACE FUNCTION myfunction (l_myvar integer[]) RETURNS mytable AS $$ DECLARE l_myrow mytable; BEGIN SELECT * INTO l_myrow FROM mytable WHERE mycol IN (array_to_string(l_myvar, ',')); RETURN l_myrow; END; $$ LANGUAGE plpgsql; Analysis reveals that although: SELECT array_to_string(ARRAY[1, 2], ','); returns 1,2 as expected SELECT * FROM myfunction(ARRAY[1, 2]); returns the error operator does not exist: integer = text at the line: WHERE mycol IN (array_to_string(l_myvar, ',')); If I execute: SELECT * FROM mytable WHERE mycol IN (1,2); I get the expected result. Given that array_to_string(l_myvar, ',') evaluates to 1,2 as shown, why arent these statements equivalent. From the error message it is something to do with datatypes, but doesnt the IN(variable) construct appear to be behaving differently from the = variable construct? What are the rules here? I know that I could build a statement to EXECUTE, treating everything as a string, to achieve what I want to do, so I am not looking for that as a solution. I do want to understand though what is going on in this example. Is there a modification to this approach to make it work, the particular example being to pass in an array of values to build a dynamic IN clause without resorting to EXECUTE? Thanks in advance Craig

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  • MySQL join problem

    - by David
    Table1 has u_name, Table2 has u_name, u_type and u_admin Table1.u_name is unique. But neither of the 3 fields in Table2 is unique. For any value of Table1.u_name, there are 0 to many entries in Table2 that Table2.u_name equals to that value. For any value of Table1.u_name, there are 0 to 1 entries in Table2 that Table2.u_name equals to that value AND Table2.u_type='S' What I want: Use Table1.u_name to get Table1.*, Table2.u_admin where Table1.u_name=Tabl2.u_name and Table2.u_type='S'. If there is no such entry in Table2 we still need to get Table1.* Please help give me some hints. Thank you so much!

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