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  • why this left join query failed to load all the data in left table ?

    - by lzyy
    users table +-----+-----------+ | id | username | +-----+-----------+ | 1 | tom | | 2 | jelly | | 3 | foo | | 4 | bar | +-----+-----------+ groups table +----+---------+-----------------------------+ | id | user_id | title | +----+---------+-----------------------------+ | 2 | 1 | title 1 | | 4 | 1 | title 2 | +----+---------+-----------------------------+ the query SELECT users.username,users.id,count(groups.title) as group_count FROM users LEFT JOIN groups ON users.id = groups.user_id result +----------+----+-------------+ | username | id | group_count | +----------+----+-------------+ | tom | 1 | 2 | +----------+----+-------------+ where is the rest users' info? the result is the same as inner join , shouldn't left join return all left table's data? PS:I'm using mysql

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  • Do a query only if there are no results on previous query

    - by yes123
    Hi guys: I do this query(1): (1)SELECT * FROM t1 WHERE title LIKE 'key%' LIMIT 1 I need to do a second(2) query only if this previous query has no results (2)SELECT * FROM t1 WHERE title LIKE '%key%' LIMIT 1 basically i need only 1 row who got the most close title to my key. Atm i am using an UNION query with a custom field to order it and a LIMIT 1. Problem is I don't want to do the others query if already the first made the result. Thanks

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  • Help on understanding multiple columns on an index?

    - by Xaisoft
    Assume I have a table called "table" and I have 3 columns, a, b, and c. What does it mean to have a non-clustered index on columns a,b? Is a nonclustered index on columns a,b the same as a nonclustered index on columns b,a? (Note the order). Also, Is a nonclustered index on column a the same as a nonclustered index on a,c? I was looking at the website sqlserver performance and they had these dmv scripts where it would tell you if you had overlapping indexes and I believe it was saying that having an index on a is the same as a,b, so it is redundant. Is this true about indexes? One last question is why is the clustered index put on the primary key. Most of the time the primary key is not queried against, so shouldn't the clustered index be on the most queried column. I am probably missing something here like having it on the primary key speeds up joins? Great explanations. Should I turn this into a wiki and change the title index explanation?

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  • Tables with no Primary Key

    - by Matt Hamilton
    I have several tables whose only unique data is a uniqueidentifier (a Guid) column. Because guids are non-sequential (and they're client-side generated so I can't use newsequentialid()), I have made a non-primary, non-clustered index on this ID field rather than giving the tables a clustered primary key. I'm wondering what the performance implications are for this approach. I've seen some people suggest that tables should have an auto-incrementing ("identity") int as a clustered primary key even if it doesn't have any meaning, as it means that the database engine itself can use that value to quickly look up a row instead of having to use a bookmark. My database is merge-replicated across a bunch of servers, so I've shied away from identity int columns as they're a bit hairy to get right in replication. What are your thoughts? Should tables have primary keys? Or is it ok to not have any clustered indexes if there are no sensible columns to index that way?

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  • LINQtoSQL Custom Constructor off Partial Class?

    - by sah302
    Hi all, I read this question here: http://stackoverflow.com/questions/82409/is-there-a-way-to-override-the-empty-constructor-in-a-class-generated-by-linqtosq Typically my constructor would look like: public User(String username, String password, String email, DateTime birthday, Char gender) { this.Id = Guid.NewGuid(); this.DateCreated = this.DateModified = DateTime.Now; this.Username = username; this.Password = password; this.Email = email; this.Birthday = birthday; this.Gender = gender; } However, as read in that question, you want to use partial method OnCreated() instead to assign values and not overwrite the default constructor. Okay so I got this : partial void OnCreated() { this.Id = Guid.NewGuid(); this.DateCreated = this.DateModified = DateTime.Now; this.Username = username; this.Password = password; this.Email = email; this.Birthday = birthday; this.Gender = gender; } However, this gives me two errors: Partial Methods must be declared private. Partial Methods must have empty method bodies. Alright I change it to Private Sub OnCreated() to remove both of those errors. However I am still stuck with...how can I pass it values as I would with a normal custom constructor? Also I am doing this in VB (converted it since I know most know/prefer C#), so would that have an affect on this?

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  • What resources will help me understand the fundamentals of Relational Database Systems.

    - by Rachel
    This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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  • Two different tables or just one with bool column?

    - by Aidas
    We have two tables: OriginalDocument and ProcessedDocument. In the first one we put an original, not processed document. After it's validated and processed (converted to our xml format and parsed), it's put into Document table. Processed document can be valid or invalid. Which makes more sense: have two different tables for valid and invalid documents or just have one with 'Valid' column? Some of the columns (~5-7) are irrelevant for invalid document. Storing both invalid and valid documents would also make Document table filled with 'NULL' columns (if document is invalid, information like document number, receiver can be unknown). What else should we consider and weigh, when making this decision?

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  • Compiled Queries and "Parameters cannot be sequences"

    - by David B
    I thought that compiled queries would perform the same query translation as DataContext. Yet I'm getting a run-time error when I try to use a query with a .Contains method call. Where have I gone wrong? //private member which holds a compiled query. Func<DataAccess.DataClasses1DataContext, List<int>, List<DataAccess.TestRecord>> compiledFiftyRecordQuery = System.Data.Linq.CompiledQuery.Compile <DataAccess.DataClasses1DataContext, List<int>, List<DataAccess.TestRecord>> ((dc, ids) => dc.TestRecords.Where(tr => ids.Contains(tr.ID)).ToList()); //this method calls the compiled query. public void FiftyRecordCompiledQueryByID() { List<int> IDs = GetRandomInts(50); //System.NotSupportedException //{"Parameters cannot be sequences."} List<DataAccess.TestRecord> results = compiledFiftyRecordQuery (myContext, IDs); }

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  • How to move from untyped DataSets to POCO\LINQ2SQL in legacy application

    - by artvolk
    Good day! I've a legacy application where data access layer consists of classes where queries are done using SqlConnection/SqlCommand and results are passed to upper layers wrapped in untyped DataSets/DataTable. Now I'm working on integrating this application into newer one where written in ASP.NET MVC 2 where LINQ2SQL is used for data access. I don't want to rewrite fancy logic of generating complex queries that are passed to SqlConnection/SqlCommand in LINQ2SQL (and don't have permission to do this), but I'd like to have result of these queries as strong-typed objects collection instead of untyped DataSets/DataTable. The basic idea is to wrap old data access code in a nice-looking from ASP.NET MVC "Model". What is the fast\easy way of doing this?

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  • Can I serialize an object if I didn't write the class used to instantiate that object?

    - by Richard77
    Hello, I've a simple class [Serializable] public class MyClass { public String FirstName { get; set: } public String LastName { get; set: } //Bellow is what I would like to do //But, it's not working //I get an exception ContactDataContext db = new ContactDataContext(); public void Save() { Contact contact = new Contact(); contact.FirstName = FirstName; contact.LastName = LastName; db.Contacts.InsertOnSubmit(contact); db.SubmitChanges(); } } I wanted to attach a Save method to the class so that I could call it on each object. When I introduced the above statement which contains ContactDataContext, I got the following error "In assembly ... PublicKeyToken=null' is not marked as serializable" It's clear that the DataContext class is generated by the framework (). I checked and did not see where that class was marked serialize. What can I do to overcome that? What's the rule when I'm not the author of a class? Just go ahead and mark the DataContext class as serializable, and pretend that everything will work? Thanks for helping

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  • privmsg system db schema

    - by Bartek
    I'm making a PM-system on my site. And I want to know ultimate db schema. I have always just used only 1 table. But my users have started complained that the messages in their outbox suddently dissapers =D Thats because if the other users deletes it, the one who sent it wont see it to. So im thinking of making another table with the same fields So im thinking something like this: privmsgs id | to | from | subject | message | date -- -- ---- ------- ------- ---- 1 76 893 blabla. blabla. 20100404 sent_msgs id | to | from | subject | message | date -- -- ---- ------- ------- ---- 1 76 893 blabla. blabla. 20100404 Whatya think? Sorry for my bad english

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  • Calling sp and Performance strategy.

    - by Costa
    Hi I find my self in a situation where I have to choose between either creating a new sp in database and create the middle layer code. so loose some precious development time. also the procedure is likely to contain some joins. Or use two existing sp(s), the problem of this approach is that I am doing two round trips to database. which can be poor performance especially if I have database in another server. Which approach you will go?, and why? thanks

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  • Displaying a single rank in MySQL table

    - by MichaelInno
    I have a table called 'highscores' that looks like this. id udid name score 1 1111 Mike 200 2 3333 Joe 300 3 4444 Billy 50 4 0000 Loser 10 5 DDDD Face 400 Given a specific udid, I want to return the rank of that row by their score value. i.e. if udid given = 0000, I should return 5. Any idea how to write this query for a MySQL database?

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  • select rows with column that is not null?

    - by fayer
    by default i have one column in mysql table to be NULL. i want to select some rows but only if the field value in that column is not NULL. what is the correct way of typing it? $query = "SELECT * FROM names WHERE id = '$id' AND name != NULL"; is this correct?

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  • Query to find all the nodes that are two steps away from a particular node.

    - by iecut
    Suppose I have two columns in a table that represents a graph, the first column is a FROMNODE and second one is TONODE. What I would like to know is that how will we find all the nodes that are two steps away from a particular node. Lets suppose I have a node numbered '1' and i would like to know all the nodes that are two steps away from it. I have tried(I am assuming the table name as graph) SELECT FROMNODE FROM GRAPH WHERE TONODE=1 (this is to select all the nodes that are connected to node 1, but I couldn't figure out how would I find all the nodes that are two steps away from node 1??)

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  • How to calculate the sum of a column in an MS Access table for a given date (a single day, month or year)

    - by cMinor
    I have a table in Access in a custom format saved as dd/MM/yyyy hh:mm:ss tt , Also A form in VB.NET 2010, I get a specific day, month and year with no problem but the problem comes when I want to query the sum of a column named value depending on a specific month or day or year.... The table is like: +-----+-----------+-------------------------+ | id | value | date | +-----+-----------+-------------------------+ | id1 | 1499 | 01/01/2012 07:30:11 p.m.| | id2 | 1509 | 11/02/2012 07:30:11 p.m.| | id3 | 1611 | 21/10/2012 07:30:11 p.m.| | id1 | 1115 | 11/10/2012 07:30:11 p.m.| | id1 | 1499 | 17/05/2012 07:30:11 p.m.| | id2 | 1709 | 11/06/2012 07:30:11 p.m.| | id3 | 1911 | 30/07/2012 07:30:11 p.m.| | id1 | 1015 | 01/08/2012 07:30:11 p.m.| | id1 | 1000 | 11/05/2012 07:30:11 p.m.| |+-----+-----------+------------------------+ So I Know the query SELECT SUM(value) FROM mytable WHERE date in='01/05/2012 00:00:00' ... How to tell the query I want the month of May so I would get 1499+1000= 2499 Or how to tell I want the year 2012 so I would get the sum of all the table Which would be the correct syntax...

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  • To log in stored procedures?

    - by hgulyan
    If you have a long running SP, do you log somehow it's actions or just wait for this message? "Command(s) completed successfully." I assume, that there can be plenty solutions on this subject, but is there any best practice - a simple solution that is frequently used?

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  • Strange: Planner takes decision with lower cost, but (very) query long runtime

    - by S38
    Facts: PGSQL 8.4.2, Linux I make use of table inheritance Each Table contains 3 million rows Indexes on joining columns are set Table statistics (analyze, vacuum analyze) are up-to-date Only used table is "node" with varios partitioned sub-tables Recursive query (pg = 8.4) Now here is the explained query: WITH RECURSIVE rows AS ( SELECT * FROM ( SELECT r.id, r.set, r.parent, r.masterid FROM d_storage.node_dataset r WHERE masterid = 3533933 ) q UNION ALL SELECT * FROM ( SELECT c.id, c.set, c.parent, r.masterid FROM rows r JOIN a_storage.node c ON c.parent = r.id ) q ) SELECT r.masterid, r.id AS nodeid FROM rows r QUERY PLAN ----------------------------------------------------------------------------------------------------------------------------------------------------------------- CTE Scan on rows r (cost=2742105.92..2862119.94 rows=6000701 width=16) (actual time=0.033..172111.204 rows=4 loops=1) CTE rows -> Recursive Union (cost=0.00..2742105.92 rows=6000701 width=28) (actual time=0.029..172111.183 rows=4 loops=1) -> Index Scan using node_dataset_masterid on node_dataset r (cost=0.00..8.60 rows=1 width=28) (actual time=0.025..0.027 rows=1 loops=1) Index Cond: (masterid = 3533933) -> Hash Join (cost=0.33..262208.33 rows=600070 width=28) (actual time=40628.371..57370.361 rows=1 loops=3) Hash Cond: (c.parent = r.id) -> Append (cost=0.00..211202.04 rows=12001404 width=20) (actual time=0.011..46365.669 rows=12000004 loops=3) -> Seq Scan on node c (cost=0.00..24.00 rows=1400 width=20) (actual time=0.002..0.002 rows=0 loops=3) -> Seq Scan on node_dataset c (cost=0.00..55001.01 rows=3000001 width=20) (actual time=0.007..3426.593 rows=3000001 loops=3) -> Seq Scan on node_stammdaten c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=0.008..9049.189 rows=3000001 loops=3) -> Seq Scan on node_stammdaten_adresse c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=3.455..8381.725 rows=3000001 loops=3) -> Seq Scan on node_testdaten c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=1.810..5259.178 rows=3000001 loops=3) -> Hash (cost=0.20..0.20 rows=10 width=16) (actual time=0.010..0.010 rows=1 loops=3) -> WorkTable Scan on rows r (cost=0.00..0.20 rows=10 width=16) (actual time=0.002..0.004 rows=1 loops=3) Total runtime: 172111.371 ms (16 rows) (END) So far so bad, the planner decides to choose hash joins (good) but no indexes (bad). Now after doing the following: SET enable_hashjoins TO false; The explained query looks like that: QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- CTE Scan on rows r (cost=15198247.00..15318261.02 rows=6000701 width=16) (actual time=0.038..49.221 rows=4 loops=1) CTE rows -> Recursive Union (cost=0.00..15198247.00 rows=6000701 width=28) (actual time=0.032..49.201 rows=4 loops=1) -> Index Scan using node_dataset_masterid on node_dataset r (cost=0.00..8.60 rows=1 width=28) (actual time=0.028..0.031 rows=1 loops=1) Index Cond: (masterid = 3533933) -> Nested Loop (cost=0.00..1507822.44 rows=600070 width=28) (actual time=10.384..16.382 rows=1 loops=3) Join Filter: (r.id = c.parent) -> WorkTable Scan on rows r (cost=0.00..0.20 rows=10 width=16) (actual time=0.001..0.003 rows=1 loops=3) -> Append (cost=0.00..113264.67 rows=3001404 width=20) (actual time=8.546..12.268 rows=1 loops=4) -> Seq Scan on node c (cost=0.00..24.00 rows=1400 width=20) (actual time=0.001..0.001 rows=0 loops=4) -> Bitmap Heap Scan on node_dataset c (cost=58213.87..113214.88 rows=3000001 width=20) (actual time=1.906..1.906 rows=0 loops=4) Recheck Cond: (c.parent = r.id) -> Bitmap Index Scan on node_dataset_parent (cost=0.00..57463.87 rows=3000001 width=0) (actual time=1.903..1.903 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_stammdaten_parent on node_stammdaten c (cost=0.00..8.60 rows=1 width=20) (actual time=3.272..3.273 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_stammdaten_adresse_parent on node_stammdaten_adresse c (cost=0.00..8.60 rows=1 width=20) (actual time=4.333..4.333 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_testdaten_parent on node_testdaten c (cost=0.00..8.60 rows=1 width=20) (actual time=2.745..2.746 rows=0 loops=4) Index Cond: (c.parent = r.id) Total runtime: 49.349 ms (21 rows) (END) - incredibly faster, because indexes were used. Notice: Cost of the second query ist somewhat higher than for the first query. So the main question is: Why does the planner make the first decision, instead of the second? Also interesing: Via SET enable_seqscan TO false; i temp. disabled seq scans. Than the planner used indexes and hash joins, and the query still was slow. So the problem seems to be the hash join. Maybe someone can help in this confusing situation? thx, R.

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  • how to use insert command in sql analysis services

    - by imcolin
    Hi all, I have a problem regarding how to use insert command in ssas, i try to send a request to server, server give a response saying "No binding exists for it", my request envelope is:- <Envelope xmlns="http://schemas.xmlsoap.org/soap/envelope/"> SSAS SsasCubes Sales Territory Sales Territory Key fds aa 1033 Should i create a attribut binding before using insert command??? any body can help me ? one more question, when i use Update command in ssas, I also got a error say "Attributes cannot appear in Where ". can you tell me why?? Thanks

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  • mysql query for getting all messages that belong to user's contacts

    - by aharon
    So I have a database that is setup sort of like this (simplified, and in terms of the tables, all are InnoDBs): Users: contains based user authentication information (uid, username, encrypted password, et cetera) Contacts: contains two rows per relationship that exists between users as (uid1, uid2), (uid2, uid1) to allow for a good 1:1 relationship (must be mutual) between users Messages: has messages that consist of a blob, owner-id, message-id (auto_increment) So my question is, what's the best MySQL query to get all messages that belong to all the contacts of a specific user? Is there an efficient way to do this?

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  • MySQL foreign key creation with alter table command

    - by user313338
    I created some tables using MySQL Workbench, and then did forward ‘forward engineer’ to create scripts to create these tables. BUT, the scripts lead me to a number of problems. One of which involves the foreign keys. So I tried creating separate foreign key additions using alter table and I am still getting problems. The code is below (the set statements, drop/create statements I left in … though I don’t think they should matter for this): SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL'; DROP SCHEMA IF EXISTS `mydb` ; CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ; -- ----------------------------------------------------- -- Table `mydb`.`User` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User` ; CREATE TABLE IF NOT EXISTS `mydb`.`User` ( `UserName` VARCHAR(35) NOT NULL , `Num_Accts` INT NOT NULL , `Password` VARCHAR(45) NULL , `Email` VARCHAR(45) NULL , `User_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_ID`) ) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `mydb`.`User_Space` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User_Space` ; CREATE TABLE IF NOT EXISTS `mydb`.`User_Space` ( `User_UserName` VARCHAR(35) NOT NULL , `User_Space_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_Space_ID`), FOREIGN KEY (`User_UserName`) REFERENCES `mydb`.`User` (`UserName`) ON UPDATE CASCADE ON DELETE CASCADE) ENGINE = InnoDB; SET SQL_MODE=@OLD_SQL_MODE; SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS; SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS; The error this produces is: Error Code: 1005 Can't create table 'mydb.user_space' (errno: 150) Anybody know what the heck I’m doing wrong?? And anybody else have problems with the script generation done by mysql workbench? It’s a nice tool, but annoying that it pumps out scripts that don’t work for me. [As an fyi here’s the script it auto-generates: SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL'; DROP SCHEMA IF EXISTS `mydb` ; CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ; -- ----------------------------------------------------- -- Table `mydb`.`User` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User` ; CREATE TABLE IF NOT EXISTS `mydb`.`User` ( `UserName` VARCHAR(35) NOT NULL , `Num_Accts` INT NOT NULL , `Password` VARCHAR(45) NULL , `Email` VARCHAR(45) NULL , `User_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_ID`) ) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `mydb`.`User_Space` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User_Space` ; CREATE TABLE IF NOT EXISTS `mydb`.`User_Space` ( `User_Space_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_Space_ID`) , INDEX `User_ID` () , CONSTRAINT `User_ID` FOREIGN KEY () REFERENCES `mydb`.`User` () ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; SET SQL_MODE=@OLD_SQL_MODE; SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS; SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS; ** Thanks!]

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