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  • Database indexes and their Big-O notation

    - by miket2e
    I'm trying to understand the performance of database indexes in terms of Big-O notation. Without knowing much about it, I would guess that: Querying on a primary key or unique index will give you a O(1) lookup time. Querying on a non-unique index will also give a O(1) time, albeit maybe the '1' is slower than for the unique index (?) Querying on a column without an index will give a O(N) lookup time (full table scan). Is this generally correct ? Will querying on a primary key ever give worse performance than O(1) ? My specific concern is for SQLite, but I'd be interested in knowing to what extent this varies between different databases too.

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  • Reducing a normalized table to one value

    - by Dio
    Hello, I'm sure this has been asked but I'm not quite sure how to properly search for this question, my apologies. I have two tables, Foo and Bar. For has one row per Food, bar has many rows per food matching descriptors. Foo name id Apple 1 Orange 2 Bar id description 1 Tasty 1 Ripe 2 Sweet etc (sorry for the somewhat contrived example). I'm trying to return a query where if, for each row in Foo, Bar contains a descriptor in ('Tasty', 'Juicy') return true ex: Output Apple True Orange False I had been solving this somewhat trivially with a case when I only had one item to match select Foo.name, case bar.description when 'Tasty' then True else 'False' end from Foo left join Bar on foo.id = bar.id where bar.description = 'Tasty' But with multiple items, I keep ending up with extra rows: Output Apple True Apple False etc etc Can someone point me in the right direction on how to think about this problem or what I should be doing? Thank you.

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  • filter by multiple attributes

    - by cosy
    I have the table : id id_products id_atribut name value 1 13 8 autdio 2.1 2 13 9 hdd 200 Gb 3 13 10 cd-rom 2 4 20 8 audio 2.1 the problem is, how can i select from this table where name="audio" and value="2.1" and name="hdd" and value="200 gb" and return id_products=13 .... How can i do this?

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  • Combining 2 Linq queries into 1

    - by Mike Fielden
    Given the following information, how can I combine these 2 linq queries into 1. Having a bit of trouble with the join statement. 'projectDetails' is just a list of ProjectDetails ProjectDetails (1 to many) PCardAuthorizations ProjectDetails (1 to many) ExpenditureDetails Notice I am grouping by the same information and selecting the same type of information var pCardAccount = from c in PCardAuthorizations where projectDetails.Contains(c.ProjectDetail) && c.RequestStatusId == 2 group c by new { c.ProjectDetail, c.ProgramFund } into g select new { Key = g.Key, Sum = g.Sum(x => x.Amount) }; var expenditures = from d in ExpenditureDetails where projectDetails.Contains(d.ProjectDetails) && d.Expenditures.ExpenditureTypeEnum == 0 group d by new { d.ProjectDetails, d.ProgramFunds } into g select new { Key = g.Key, Sum = g.Sum(y => y.ExpenditureAmounts.FirstOrDefault(a => a.IsCurrent && !a.RequiresAudit).CommittedMonthlyRecords.ProjectedEac) };

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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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  • Check if row already exists, if so tell the referenced table the id

    - by flhe
    Let's assume I have a table magazine: CREATE TABLE magazine ( magazine_id integer NOT NULL DEFAULT nextval(('public.magazine_magazine_id_seq'::text)::regclass), longname character varying(1000), shortname character varying(200), issn character varying(9), CONSTRAINT pk_magazine PRIMARY KEY (magazine_id) ); And another table issue: CREATE TABLE issue ( issue_id integer NOT NULL DEFAULT nextval(('public.issue_issue_id_seq'::text)::regclass), number integer, year integer, volume integer, fk_magazine_id integer, CONSTRAINT pk_issue PRIMARY KEY (issue_id), CONSTRAINT fk_magazine_id FOREIGN KEY (fk_magazine_id) REFERENCES magazine (magazine_id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION ); Current INSERTS: INSERT INTO magazine (longname,shotname,issn) VALUES ('a long name','ee','1111-2222'); INSERT INTO issue (fk_magazine_id,number,year,volume) VALUES (currval('magazine_magazine_id_seq'),'8','1982','6'); Now a row should only be inserted into 'magazine', if it does not already exist. However if it exists, the table 'issue' needs to get the 'magazine_id' of the row that already exists in order to establish the reference. How can i do this? Thx in advance!

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  • t-sql get variable value from string with variable name

    - by Markus
    Hi. Is there a way to convert '@my_variable' string into a value of @my_variable? I have a table which stores names of variables. I need to get the value of this variable. Something like this: DECLARE @second_variable AS NVARCHAR(20); DECLARE @first_variable AS NVARCHAR(20); SET @first_variable = '20'; SET @second_variable = SELECT '@first_variable'; --here I want that @second variable be assigned a value of "20".

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  • Removing "Using temporary; Using filesort" from this MySQL select+join+group by query

    - by claytontstanley
    I have the following query: select t.Chunk as LeftChunk, t.ChunkHash as LeftChunkHash, q.Chunk as RightChunk, q.ChunkHash as RightChunkHash, count(t.ChunkHash) as ChunkCount from chunksubset as t join chunksubset as q on t.ID = q.ID group by LeftChunkHash, RightChunkHash And the following explain table: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE subsets ref PRIMARY,IDIndex,SubsetIndex SubsetIndex 767 const 522014 "Using where; Using temporary; Using filesort" 1 SIMPLE subsets eq_ref PRIMARY,IDIndex,SubsetIndex PRIMARY 771 sotero.subsets.Id,const 1 "Using where; Using index" 1 SIMPLE c ref IDIndex IDIndex 4 sotero.subsets.Id 12 "Using where" 1 SIMPLE c ref IDIndex IDIndex 4 sotero.subsets.Id 12 note the "using temporary; using filesort". When this query is run, I quickly run out of RAM (presumably b/c of the temp table), and then the HDD kicks in, and the query slows to a halt. I thought it might be an index issue, so I started adding a few that sort of made sense: Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment chunks 0 PRIMARY 1 ChunkId A 17796190 NULL NULL BTREE chunks 1 ChunkHashIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 IDIndex 1 Id A 1483015 NULL NULL BTREE chunks 1 ChunkIndex 1 Chunk A 243783 NULL NULL BTREE chunks 1 ChunkTypeIndex 1 ChunkType A 2 NULL NULL BTREE chunks 1 chunkHashByChunkIDIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 chunkHashByChunkIDIndex 2 ChunkId A 17796190 NULL NULL BTREE chunks 1 chunkHashByChunkTypeIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 chunkHashByChunkTypeIndex 2 ChunkType A 261708 NULL NULL BTREE chunks 1 chunkHashByIDIndex 1 ChunkHash A 243783 NULL NULL BTREE chunks 1 chunkHashByIDIndex 2 Id A 17796190 NULL NULL BTREE But still using the temporary table. The db engine is MyISAM. How can I get rid of the using temporary; using filesort in this query? Just changing to InnoDB w/o explaining the underlying cause is not a particularly satisfying answer. Besides, if the solution is to just add the proper index, then that's much easier than migrating to another db engine.

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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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  • Postgesql select from 2 tables. Joins?

    - by Daniel
    I have 2 tables that look like this: Table "public.phone_lists" Column | Type | Modifiers ----------+-------------------+-------------------------------------------------------------------- id | integer | not null default nextval(('"phone_lists_id_seq"'::text)::regclass) list_id | integer | not null sequence | integer | not null phone | character varying | name | character varying | and Table "public.email_lists" Column | Type | Modifiers ---------+-------------------+-------------------------------------------------------------------- id | integer | not null default nextval(('"email_lists_id_seq"'::text)::regclass) list_id | integer | not null email | character varying | I'm trying to get the list_id, phone, and emails out of the tables in one table. I'm looking for an output like: list_id | phone | email ---------+-------------+-------------------------------- 0 | | [email protected] 0 | | [email protected] 0 | | [email protected] 0 | | [email protected] 0 | | [email protected] 1 | 15555555555 | 1 | 15555551806 | 1 | 15555555508 | 1 | 15055555506 | 1 | 15055555558 | 1 | | [email protected] 1 | | [email protected] I've come up with select pl.list_id, pl.phone, el.email from phone_lists as pl left join email_lists as el using (list_id); but thats not quite right. Any suggestions?

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  • how to Solve the "Digg" problem in MongoDB

    - by user193116
    A while back,a Digg developer had posted this blog ,"http://about.digg.com/blog/looking-future-cassandra", where the he described one of the issues that were not optimally solved in MySQL. This was cited as one of the reasons for their move to Cassandra. I have been playing with MongoDB and I would like to understand how to implement the MongoDB collections for this problem From the article, the schema for this information in MySQL : CREATE TABLE Diggs ( id INT(11), itemid INT(11), userid INT(11), digdate DATETIME, PRIMARY KEY (id), KEY user (userid), KEY item (itemid) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE TABLE Friends ( id INT(10) AUTO_INCREMENT, userid INT(10), username VARCHAR(15), friendid INT(10), friendname VARCHAR(15), mutual TINYINT(1), date_created DATETIME, PRIMARY KEY (id), UNIQUE KEY Friend_unique (userid,friendid), KEY Friend_friend (friendid) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; This problem is ubiquitous in social networking scenario implementation. People befriend a lot of people and they in turn digg a lot of things. Quickly showing a user what his/her friends are up to is very critical. I understand that several blogs have since then provided a pure RDBMs solution with indexes for this issue; however I am curious as to how this could be solved in MongoDB.

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  • url Query and Security

    - by jasmine
    In url query with id I use is_numeric($_GET['id']) for security issues. But in query with for example category name, is urlencode() a right way for security? Thanks in advance.

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  • Free tool to watch database for changes?

    - by 01
    Im looking for a tool that can watch database(mysql and oracle) for changes. When someone inserts or updates something in any table i want to get to know about it. I know that it can be done using triggers(http://stackoverflow.com/questions/167254/watching-a-table-for-change-in-mysql), but im more interested in some tool that can do it. free tool.

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  • Storing users in a database

    - by EMcKenna
    Im wondering whats the best way of storing different types of users in my database. I am writing an application that has 4 main user types (admin, school, teacher, student). At the moment I have a table for each of these but i'm not sure thats the best way of storing user information. For instance... Allowing students to PM other student is simple (store sender and receiver student_id) but enabling teachers to PM students requires another table (sender teacher_id, sender student_id). Should all users be stored in one users table with a user_type field? If so, the teacher / student specific information will still have to be stored in another table. users user_id, password_hash, user_type students user_id, student_specific_stuff... teachers user_id, teacher_specific_stuff... How do I stop a user who has a user_type = student from being accidentally being entered into the teachers table (as both have a user_id) Just want to make sure I get the database correct before i go any further. Thanks...

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  • INSERT data from Textbox to Postgres SQL

    - by user1479013
    I just learn how to connect C# and PostgresSQL. I want to INSERT data from tb1(Textbox) and tb2 to database. But I don't know how to code My previous code is SELECT from database. this is my code private void button1_Click(object sender, EventArgs e) { bool blnfound = false; NpgsqlConnection conn = new NpgsqlConnection("Server=127.0.0.1;Port=5432;User Id=postgres;Password=admin123;Database=Login"); conn.Open(); NpgsqlCommand cmd = new NpgsqlCommand("SELECT * FROM login WHERE name='" + tb1.Text + "' and password = '" + tb2.Text + "'",conn); NpgsqlDataReader dr = cmd.ExecuteReader(); if (dr.Read()) { blnfound = true; Form2 f5 = new Form2(); f5.Show(); this.Hide(); } if (blnfound == false) { MessageBox.Show("Name or password is incorrect", "Message Box", MessageBoxButtons.OK, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1); dr.Close(); conn.Close(); } } So please help me the code.

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  • Slow query with unexpected scan

    - by zerkms
    Hello I have this query: SELECT * FROM SAMPLE SAMPLE INNER JOIN TEST TEST ON SAMPLE.SAMPLE_NUMBER = TEST.SAMPLE_NUMBER INNER JOIN RESULT RESULT ON TEST.TEST_NUMBER = RESULT . TEST_NUMBER WHERE SAMPLED_DATE BETWEEN '2010-03-17 09:00' AND '2010-03-17 12:00' the biggest table here is RESULT, contains 11.1M records. The left 2 tables about 1M. this query works slowly (more than 10 minutes) and returns about 800 records. executing plan shows clustered index scan over all 11M records. RESULT.TEST_NUMBER is a clustered primary key. if I change 2010-03-17 09:00 to 2010-03-17 10:00 - i get about 40 records. it executes for 300ms. and plan shows clustered index seek if i replace * in SELECT clause to RESULT.TEST_NUMBER (covered with index) - then all become fast in first case too. this points to hdd io issues, but doesn't clarifies changing plan. so, any ideas?

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  • How can I format Custom Data and display in autocomplete when source is an DB

    - by Andres Scarpone
    so I'm trying to get some info in the auto-complete widget like it's shown in the JQuery UI demo Demo, the only problem is they use a variable that they fill with the data they want to show, I instead want to access the data and the different description and stuff using a Data Base in MySQL, for this I have changed the source to use another php page that looks up the info. here is the code for the Auto-complete, I really don't understand the methods so I haven't changed it from the basic search. This is the JS: $(document).ready((function(){ $( "#completa" ).autocomplete({ source: "buscar.php", minLength: 1, focus: function (event, ui){ $("#completa").val(ui.item.val); return false; }; })); This is what I have in buscar.php: <?php $conec = mysql_connect(localhost, root, admin); if(!$conec) { die(mysql_error()); } else { $bd = mysql_select_db("ve_test",$conec ); if(!$bd) { die(mysql_error()); } } $termino = trim(strip_tags($_GET['term']));//Obtener el termino que envia el autocompletar $qstring = "SELECT name, descripcion FROM VE_table WHERE name LIKE '%".$termino."%'"; $result = mysql_query($qstring);//Solicitud a la Base de Datos while ($row = mysql_fetch_array($result,MYSQL_ASSOC))//Realizar un LOOP sobre los valores obtenidos { $row['value']=htmlentities(stripslashes($row['name'])); $row_set[] = $row;//build an array } echo json_encode($row_set);//Enviar los datos al autocompletar en codificacion JSON, Altamente Necesario. ?

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  • MySQL Count If using 4 tables or Perl

    - by user1726133
    Hi I have a relatively convoluted query that relies on 4 different tables, unfortunately I do not have control of this data, but I do have to query it. I ran this simpler query and it works using just table 1 and table 2 SELECT actor, receiver, count(IF(t2.group1 = "anxiety behavior", 1,0)) AS 'anxiety' FROM ethogram_edited_obs_behaviors t1 JOIN ethogram_behaviors t2 on t1.behavior = t2.behavior_code GROUP BY actor; Below are the 4 tables I need and the query I tried that didn't work Table 1 | Table 2 | Table 3 | Table 4 Actor | Behavior | Behavior | type of Behavior | subject | sex | subject |subject_code er frown | frown anxiety behavior | Eric M | Eric | er Here is the query that is failing SELECT actor, count(IF(t2.group1 = "anxiety behavior", 1,0) AND(t3.sex = "M", 1,0)) AS 'anxiety', FROM ethogram_edited_obs_behaviors t1 JOIN ethogram_behaviors t2 on t1.behavior = t2.behavior_code JOIN subject_code t3 on t1.actor = t3.behavior_code1 JOIN subjects t4 on t3.subject = t4.yerkes_code GROUP BY actor; Any help would be much appreciated!! Thanks :) P.S. if this is easier to do in Perl tips also much appreciated

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  • SaaS Multi-tenancy Applications: How is data import/export/backup being implemented?

    - by Mark Redman
    How are applications providing import / export (or backups) of data in SaaS based multi-tenancy applications, particularly single database designs? Imports: Keeping things simple I think basic imports are useful, ie CSV to a spec (or a way of providing a mapping between CSV columns and fields in the database. Exports: In single database designs I have seen XML exports and HTML (basic sitse generated) exports of data? I would assume that XML is a better option? How does one cater for relational data? Would you reference various things within XML and provide documentation of the relationships or let users figurethis out? Are vendors providing an export/backup that can be imported back in/restored? Your comments appreciated.

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  • Can't register credit card with Microsoft Windows Azure

    - by user1083268
    I get the following error when trying to sign up for the Microsoft Azure 90-day free trial: We can't authorize the payment method. Please make sure the information is correct, or use another payment method. If you continue to get this message, please contact your financial institution. I've tried three different cards, two credit and one debit. Those cards are issued from two different banks. I've also tried the cards on two separate accounts. Someone from my work also confirmed that he could not sign up for the free trial either. Has anyone else had this problem? I haven't really seen much help searching Google and the support staff doesn't seem interested in helping people sign up for free accounts.

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