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  • MySQL won't use index for query?

    - by Jack Sleight
    I have this table: CREATE TABLE `point` ( `id` INT(11) NOT NULL AUTO_INCREMENT, `siteid` INT(11) NOT NULL, `lft` INT(11) DEFAULT NULL, `rgt` INT(11) DEFAULT NULL, `level` SMALLINT(6) DEFAULT NULL, PRIMARY KEY (`id`), KEY `point_siteid_site_id` (`siteid`), CONSTRAINT `point_siteid_site_id` FOREIGN KEY (`siteid`) REFERENCES `site` (`id`) ON DELETE CASCADE ) ENGINE=INNODB AUTO_INCREMENT=35 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci And this query: SELECT * FROM `point` WHERE siteid = 1; Which results in this EXPLAIN information: +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ | 1 | SIMPLE | point | ALL | point_siteid_site_id | NULL | NULL | NULL | 6 | Using where | +----+-------------+-------+------+----------------------+------+---------+------+------+-------------+ Question is, why isn't the query using the point_siteid_site_id index?

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  • JPA entity design / cannot delete entity

    - by timaschew
    I though its simple what I want, but I cannot find any solution for my problem. I'm using playframework 1.2.3 and it's using Hibernate as JPA. So I think playframework has nothing to do with the problem. I have some classes (I omit the nonrelevant fields) public class User { ... } public class Task { public DataContainer dataContainer; } public class DataContainer { public Session session; public User user; } public class Session { ... } So I have association from Task to DataContainer and from DataContainer to Sesssion and the DataContainer belongs to a User. The DataContainers can have always the same User, but the Session have to be different for each instance. And the DataContainer of a Task have also to be different in each instance. A DataContainer can have a Sesesion or not (it's optinal). I use only unidirectional assoc. It should be sufficient. In other words: Every Task must has one DataContainer. Every DataContainer must has one/the same User and can have one Session. To create a DB schema I use JPA annotations: @Entity public class User extends Model { ... } @Entity public class Task extends Model { @OneToOne(optional = false, cascade = CascadeType.ALL) public DataContainer dataContainer; } @Entity public class DataContainer extends Model { @OneToOne(optional = true, cascade = CascadeType.ALL) public Session session; @ManyToOne(optional = false, cascade = CascadeType.ALL) public User user; } @Entity public class Session extends Model { ... } BTW: Model is a play class and provides the primary id as long type. When I create some for each entity a object and 'connect them', I mean the associations, it works fine. But when I try to delete a Session, I get a constraint violation exception, because a DataContainer still refers to the Session I want to delete. I want that the Session (field) of the DataContainer will be set to null respectively the foreign key (session_id) should be unset in the database. This will be okay, because its optional. I don't know, I think I have multiple problems. Am I using the right annotation @OneToOne ? I found on the internet some additional annotation and attributes: @JoinColumn and a mappedBy attribute for the inverse relationship. But I don't have it, because its not bidirectional. Or is a bidirectional assoc. essentially? Another try was to use @OnDelete(action = OnDeleteAction.CASCADE) the the contraint changed from NO ACTIONs when update or delete to: ADD CONSTRAINT fk4745c17e6a46a56 FOREIGN KEY (session_id) REFERENCES annotation_session (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE CASCADE; But in this case, when I delete a session, the DataContainer and User is deleted. That's wrong for me. EDIT: I'm using postgresql 9, the jdbc stuff is included in play, my only db config is db=postgres://app:app@localhost:5432/app

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  • MySQL forgot about automatically creating an index for a foreign key?

    - by bobo
    After running the following SQL statements, you will see that, MySQL has automatically created the non-unique index question_tag_tag_id_tag_id on the tag_id column for me after the first ALTER TABLE statement has run. But after the second ALTER TABLE statement has run, I think MySQL should also automatically create another non-unique index question_tag_question_id_question_id on the question_id column for me. But as you can see from the SHOW INDEXES statement output, it's not there. Why does MySQL forget about the second ALTER TABLE statement? By the way, since I have already created a unique index question_id_tag_id_idx used by both question_id and tag_id columns. Is creating a separate index for each of them redundant? mysql> DROP DATABASE mydatabase; Query OK, 1 row affected (0.00 sec) mysql> CREATE DATABASE mydatabase; Query OK, 1 row affected (0.00 sec) mysql> USE mydatabase; Database changed mysql> CREATE TABLE question (id BIGINT AUTO_INCREMENT, html TEXT, PRIMARY KEY(id)) ENGINE = INNODB; Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE tag (id BIGINT AUTO_INCREMENT, name VARCHAR(10) NOT NULL, UNIQUE INDEX name_idx (name), PRIMARY KEY(id)) ENGINE = INNODB; Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE question_tag (question_id BIGINT, tag_id BIGINT, UNIQUE INDEX question_id_tag_id_idx (question_id, tag_id), PRIMARY KEY(question_id, tag_id)) ENGINE = INNODB; Query OK, 0 rows affected (0.00 sec) mysql> ALTER TABLE question_tag ADD CONSTRAINT question_tag_tag_id_tag_id FOREIGN KEY (tag_id) REFERENCES tag(id); Query OK, 0 rows affected (0.10 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> ALTER TABLE question_tag ADD CONSTRAINT question_tag_question_id_question_id FOREIGN KEY (question_id) REFERENCES question(id); Query OK, 0 rows affected (0.13 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> SHOW INDEXES FROM question_tag; +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | question_tag | 0 | PRIMARY | 1 | question_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | PRIMARY | 2 | tag_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | question_id_tag_id_idx | 1 | question_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 0 | question_id_tag_id_idx | 2 | tag_id | A | 0 | NULL | NULL | | BTREE | | | question_tag | 1 | question_tag_tag_id_tag_id | 1 | tag_id | A | 0 | NULL | NULL | | BTREE | | +--------------+------------+----------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 5 rows in set (0.01 sec) mysql>

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  • Get a random subset from a set in F#

    - by Cay
    I am trying to think of an elegant way of getting a random subset from a set in F# Any thoughts on this? Perhaps this would work: say we have a set of 2x elements and we need to pick a subset of y elements. Then if we could generate an x sized bit random number that contains exactly y 2n powers we effectively have a random mask with y holes in it. We could keep generating new random numbers until we get the first one satisfying this constraint but is there a better way?

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  • Check if Database raises a particular exception

    - by mcabral
    using Nhibernate; I'm trying to insert several values a on table which has an unique index on some columns. I'd like to know if a particular insert raises an exception for having violated the unique constraint. So, which particular exception type should i catch? I only want to catch this particular one and let all others go up. Thanks a lot!

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  • ASp.NET Dropdown and Dictionary

    - by Lijo
    Hi Team, I am using a dropdown list in ASP.NET with C#. I am trying to bind a dictionary to the dropdownlist. How can we specify the "Text" (key of dictionary as Text of drop down) and "value" (value as Value) for the dropdown? Could you please help? Note: There is a constraint that a class should not be introduced for this purpose. That is why I am trying to use a dictionary. Thanks Lijo

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  • Many to Many delete in NHibernate two parents with common association

    - by Joshua Grippo
    I have 3 top level entities in my app: Circuit, Issue, Document Circuits can contain Documents and Issues can contain Documents. When I delete a Circuit, I want it to delete the documents associated with it, unless it is used by something else. I would like this same behavior with Issues. I have it working when the only association is in the same table in the db, but if it is in another table, then it fails due to foreign key constraints. ex 1(This will cascade properly, because there is only a foreign constraint from Circuit to Document) Document1 exists. Circuit1 exists and contains a reference to Document1. If I delete Circuit1 then it deletes Document1 with it. ex 2(This will cascade properly, because there is only a foreign constraint from Circuit to Document.) Document1 exists. Circuit1 exists and contains a reference to Document1. Circuit2 exists and contains a reference to Document1. If I delete Circuit1 then it is deleted, but Document1 is not deleted because Circuit2 exists. If I then delete Circuit2, then Document1 is deleted. ex 3(This will throw an error, because when it deletes the Circuit it sees that there are no other circuits that reference the document so it tries to delete the document. However it should not, because there is an Issue that has a foreign constraint to the document.) Document 1 exists. Circuit1 exists and contains a reference to Document1. Issue1 exists and contains a reference to Document1. If I delete Circuit1, then it fails, because it tries to delete Document1, but Issues1 still has a reference. DB: This think won't let upload an image, so here is the ERD to the DB: http://lh3.ggpht.com/_jZWhe7NXay8/TROJhOd7qlI/AAAAAAAAAGU/rkni3oEANvc/CircuitIssues.gif Model: public class Circuit { public virtual int CircuitID { get; set; } public virtual string CJON { get; set; } public virtual IList<Document> Documents { get; set; } } public class Issue { public virtual int IssueID { get; set; } public virtual string Summary { get; set; } public virtual IList<Model.Document> Documents { get; set; } } public class Document { public virtual int DocumentID { get; set; } public virtual string Data { get; set; } } Mapping Files: <?xml version="1.0" encoding="utf-8"?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Model" assembly="Model"> <class name="Circuit" table="Circuit"> <id name="CircuitID"> <column name="CircuitID" not-null="true"/> <generator class="identity" /> </id> <property name="CJON" column="CJON" type="string" not-null="true"/> <bag name="Documents" table="CircuitDocument" cascade="save-update,delete-orphan"> <key column="CircuitID"/> <many-to-many class="Document"> <column name="DocumentID" not-null="true"/> </many-to-many> </bag> </class> </hibernate-mapping> <?xml version="1.0" encoding="utf-8"?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Model" assembly="Model"> <class name="Issue" table="Issue"> <id name="IssueID"> <column name="IssueID" not-null="true"/> <generator class="identity" /> </id> <property name="Summary" column="Summary" type="string" not-null="true"/> <bag name="Documents" table="IssueDocument" cascade="save-update,delete-orphan"> <key column="IssueID"/> <many-to-many class="Document"> <column name="DocumentID" not-null="true"/> </many-to-many> </bag> </class> </hibernate-mapping> <?xml version="1.0" encoding="utf-8"?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Model" assembly="Model"> <class name="Document" table="Document"> <id name="DocumentID"> <column name="DocumentID" not-null="true"/> <generator class="identity" /> </id> <property name="Data" column="Data" type="string" not-null="true"/> </class> </hibernate-mapping> Code: using (ISession session = sessionFactory.OpenSession()) { var doc = new Model.Document() { Data = "Doc" }; var circuit = new Model.Circuit() { CJON = "circ" }; circuit.Documents = new List<Model.Document>(new Model.Document[] { doc }); var issue = new Model.Issue() { Summary = "iss" }; issue.Documents = new List<Model.Document>(new Model.Document[] { doc }); session.Save(circuit); session.Save(issue); session.Flush(); } using (ISession session = sessionFactory.OpenSession()) { foreach (var item in session.CreateCriteria<Model.Circuit>().List<Model.Circuit>()) { session.Delete(item); } //this flush fails, because there is a reference to a child document from issue session.Flush(); foreach (var item in session.CreateCriteria<Model.Issue>().List<Model.Issue>()) { session.Delete(item); } session.Flush(); }

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  • Trasnfer of dirctory structure on network

    - by singh
    Hi I am designing a remote CD/DVD burner to address hardware constraint on my Machine. My design work like that :(Analogous to network paper printer) Unix Based Machine (acts as server) hosts a burner. Windows based machine acts as client. Client prepare data to be burn and transfer it to server. Server burn the data on CD/DVD. My Question is : . Which is the best protocol to transfer data over network (Keeping same Directory hierarchy) between different OS

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  • How to use Unique Composite Key

    - by LifeH2O
    I have a table Item(ItemName*, ItemSize*, Price, Notes) I was making composite key of (ItemName,ItemSize) to uniquely identify item. And now after reading some answers on stackoverflow suggesting the use of UNIQUE i revised it as Item(ItemID*, ItemName, ItemSize, Price, Notes) But How to apply UNIQUE constraint on ItemName and ItemSize please correct if there is something wrong in question

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  • Postgresql 9.1: ERROR: type "citext" does not exist

    - by gotuskar
    I am trying to execute following query through PgAdmin utility. CREATE TABLE svcr."EventLogs" ("eventId" BIGINT NOT NULL, "eventTime" TIMESTAMP WITH TIME ZONE NOT NULL, "userid" CITEXT, "realmid" CITEXT NOT NULL, "onUserid" CITEXT, "description" TEXT, CONSTRAINT eventlogs_pkey PRIMARY KEY ("eventId")); And I get following error - ERROR: type "citext" does not exist SQL state: 42704 Character: 120 However, following query runs fine - CREATE TABLE svcr."CategoryMap" ("category" INT NOT NULL, "userData" INT NOT NULL); What is wrong with the first query?

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  • App Engine Django Form Uniqueness Validation?

    - by GeekTantra
    Is there a simpler way to use uniqueness validation with Django Forms in AppEngine? I understand that performance would be problem if we keep an uniqueness constraint but since the amount of data being added is very small performance is not a big concern, rather development time is a concern here. Any help is appreciated.

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  • B-trees, databases, sequential inputs, and speed.

    - by IanC
    I know from experience that b-trees have awful performance when data is added to them sequentially (regardless of the direction). However, when data is added randomly, best performance is obtained. This is easy to demonstrate with the likes of an RB-Tree. Sequential writes cause a maximum number of tree balances to be performed. I know very few databases use binary trees, but rather used n-order balanced trees. I logically assume they suffer a similar fate to binary trees when it comes to sequential inputs. This sparked my curiosity. If this is so, then one could deduce that writing sequential IDs (such as in IDENTITY(1,1)) would cause multiple re-balances of the tree to occur. I have seen many posts argue against GUIDs as "these will cause random writes". I never use GUIDs, but it struck me that this "bad" point was in fact a good point. So I decided to test it. Here is my code: SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[T1]( [ID] [int] NOT NULL CONSTRAINT [T1_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO CREATE TABLE [dbo].[T2]( [ID] [uniqueidentifier] NOT NULL CONSTRAINT [T2_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO declare @i int, @t1 datetime, @t2 datetime, @t3 datetime, @c char(300) set @t1 = GETDATE() set @i = 1 while @i < 2000 begin insert into T2 values (NEWID(), @c) set @i = @i + 1 end set @t2 = GETDATE() WAITFOR delay '0:0:10' set @t3 = GETDATE() set @i = 1 while @i < 2000 begin insert into T1 values (@i, @c) set @i = @i + 1 end select DATEDIFF(ms, @t1, @t2) AS [Int], DATEDIFF(ms, @t3, getdate()) AS [GUID] drop table T1 drop table T2 Note that I am not subtracting any time for the creation of the GUID nor for the considerably extra size of the row. The results on my machine were as follows: Int: 17,340 ms GUID: 6,746 ms This means that in this test, random inserts of 16 bytes was almost 3 times faster than sequential inserts of 4 bytes. Would anyone like to comment on this? Ps. I get that this isn't a question. It's an invite to discussion, and that is relevant to learning optimum programming.

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  • I am looking for a System level activity logging application for Symbian

    - by Prashant
    Is there any free application available for logging all the activity ( both user initiated and system initiated ) on Symbian along with state of various resource variables on device (like Memory , I/O, Media player etc ). I want to use it to examine if there is any dependency /conflict /resource constraint when multiple Application are running . Any pointer in this direction will be greatly appreciated .

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  • Django - 2 fields unique together

    - by webvulture
    Suppose, I want to record say poll choices by users everyday. In this case, i have a table named vote which has columns poll , choice and user-id . So how can i out the constraint (maybe in the django models or wherever possible) that poll and user-id both should not be the same for any entry but like the same user can vote for various different polls once and obviously various users can vote for the same poll. I hope I am clear.

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  • How do I limit JPQ output?

    - by den-javamaniac
    I need to limit number of entities returned by a query to some certain value inside a JPA query (through JPQL). Particularly: select m from Manual m //constraint e.g. in sql (mysql syntax) I would do it like: select * from Manual limit 1 The only solution that comes up is simply to get all entities and then choose first one, which is out of the issue. Any ideas?

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  • Does table (string, string) require index?

    - by abatishchev
    In my database running on SQL Server 2008 R2 I have a special table for global variables: CREATE TABLE global_variables ( name NVARCHAR(50), value NVARCHAR(50) NOT NULL CONSTRAINT PK_global_variables PRIMARY KEY CLUSTERED ( name ASC ) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO Does such table require indexing on value or not?

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  • postgresql insert value in table in serial value

    - by Jesse Siu
    my database using postgresql. the table pk is uing serial value.if i want to insert a record in table, do i need type pk or it will automatic contain id. Can you give me a example about how to insert a record in dataset CREATE TABLE dataset ( id serial NOT NULL, age integer NOT NULL, name character varying(32) NOT NULL, description text NOT NULL DEFAULT ''::text CONSTRAINT dataset_pkey PRIMARY KEY (id ) )

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  • Foreign Keys in SQLITE in the Google Gears framework

    - by Maxim Gershkovich
    Hi all, Could someone please tell me why the following foreign key constraint (although executes fine) is not enforced by SQLITE? Could someone pleasse provide an example of how I can go about enforcing the relationship? CREATE TABLE User (UserID TEXT Unique NOT NULL PRIMARY KEY, FirstName TEXT NOT NULL, LastName TEXT NOT NULL, Username TEXT NOT NULL, Password TEXT NOT NULL, Email TEXT NOT NULL, SignupDate TEXT NOT NULL) CREATE TABLE Category (CategoryID TEXT Unique NOT NULL PRIMARY KEY, UserID TEXT, FOREIGN KEY(UserID) REFERENCES User(UserID))

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  • Not able to add column value

    - by peter
    I have project which contain 4 tables among these shedule table Session column i am not able to add vaue,,this table contain three foriegn key from two tables(in which single table has two foreign keys here) i added values here..Any one has any idea about this..Actually my intention is to remove the error "the insert statement conflicted with the foreign key constraint sql server"

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  • Using a model to represent the overall state of a view

    - by James P.
    Is there a standard practise for representing the state of a user interface that is not linked to a single Component? For example, a Swing interface could have a series of tabs with a constraint that a single tab should only be displayed once per a given entity type (this could be represented as a HashSet). Or a message could give the result of the last operation carried out. Or a JPanel could be linked to a single entity instance for editing purposes.

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  • Is there a command to test an SQL query without executing it? ( MySQL or ANSI SQL )

    - by Petruza
    Is there anything like this: TEST DELETE FROM user WHERE somekey = 45; That can return any errors, for example that somekey doesn't exist, or some constraint violation or anything, and reporting how many rows would be affected, but not executing the query? I know you can easily turn any query in a select query that has no write or delete effect in any row, but that can lead to errors and it's not very practical if you want to test and debug many queries.

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