In relational database design, a primary key can uniquely identify each row in a table. A primary key comprises a single column or a set of columns.

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Listing indexes and constraints

I am looking at a SQL Server database for an application I have inherited. I have not looked into SQL Server for approximately 10 years, so please bear with me. The database table I am looking at has ...
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What's better here - a single column or multicolumn primary key?

Let's assume you have a table groups and a table item. Each item belongs to exactly one group. It is an inherent part of that group. An item cannot exist outside of a group and it cannot be moved to ...
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postgresql bigserial or sequence using jpa

I'm a java developer working with jpa, before to define the indexes in my entities i would like to known which one is faster o better to use?.
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How do I validate all my constraints in postgresql?

It seems like I have been bitten by the first bug described in the release notes of postgresql 9.3.4: http://www.postgresql.org/docs/devel/static/release-9-3-4.html I now have e.g. duplicate primary ...
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EAV-like table with both primary column pointing to the same foreign column

Background: I'm a programmer who, while had to work with simple databases several times, never had to work with complex ones. I.e. I'm proficient with basic stuff, but clueless about advanced features ...
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Column suitable for natural key?

I have read many articles now about natural vs surrogate primary keys, and came to the conclusion there is no single best practice. I have a table that will have around 2000 definite unique values, ...
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191 views

What could cause an auto increment primary key to skip numbers?

I have a table created with the following T-SQL: CREATE TABLE [dbo].[TableName]( [id] [int] IDENTITY(1,1) NOT NULL PRIMARY KEY CLUSTERED ( [id] ASC )WITH (PAD_INDEX = OFF, ...
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Converting UUID's from CHAR(32) to BIN(16)

I have a few questions relating to UUID's, but before I go on, let me explain our schema a bit, first, we're on MySQL 5.5 (Percona's version to be exact)... In each applicable table, we use a two ...
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primary key: username+current time or serial

I need to choose a primary key, but I'm not sure what the best option would be. Currently I'm in a scenario where a user has machines (workers) calculating hashes. For each user I track the current ...
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159 views

Why does InnoDB table by default uses the UNIQUE constraint instead of the PRIMARY KEY?

In my MySQL database I have a table with 4 columns, the PRIMRAY KEY, two columns with a FOREIGN KEY CONSTRAINT and one UNIQUE index on all fields except for the PRIMARY KEY. The SHOW CREATE TABLE: ...
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Primary keys optimized for database sync

I am implementing lazy multi-master database synchronization in star shape network using SymmetricDS. I can not estimate the number of nodes, so I can't use simple auto-increment integers. Database ...
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1answer
45 views

one to one relationship

This is my database structure: Users {user_id, username} Profiles {profile_id, user_id, user_views} My question is: If I do it the way mentioned above, should I to set user_id as primary key or ...
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Can one part of a multi-column primary key be used across tables?

I want to use SQLite as file format for my app, a reporting program. Below is an idea of the kind of schema I'll use (just the first few tables). There will be one report per file and all tables are ...
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1answer
61 views

Proper implementation of child (derived) table PK/FK during single and multiple inheritance hard coded generalization physical data model

Below is an image of hard coded generalization UML logical model of entities. I'd like to implement these classes as tables in a physical data model. Two derived classes/entities (Class2 and ...
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2answers
159 views

Best practice to avoid a composite key?

Suppose my students fill every year a survey, containing some questions (called fields) which answer is real-valued (called value). Every student may answer the survey, at most once a year. A simple ...
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1answer
54 views

How are auto_increment keys handled in INSERT (SELECT * FROM…)

I have table1 and table2 in MySQL. Both have a primary auto_increment key id. If the table schemas match and I do INSERT INTO table1 (SELECT * FROM table2) what happens with regards to the new rows ...
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35 views

Can a complex primary key made up of 4 fields have only one of this fields set to AUTO INCREMENT?

I have a complex primary key, I wonder if what I write in the title is possible: I have a look up table with 4 fields (they should compose the primary key of the table): 1) an INT column; 2) ...
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Is matriculation number a good primary key?

I am trying to design a grade assignment database and i am facing the following dilemma. I have a student table which has the following characteristics: matriculation number which i know for a fact ...
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Platform independent select ordered by primary key

Is there a reasonably standard way to perform a select on a single table and have the result set ordered by primary key without having to specify the primary key condition explicitly? Ideally I wish ...
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64 views

Primary key for link/junction table with time-dependent data

I want to link two tables in such a way that for any given time period the relationship is one-to-one, but over time the relationship can change. As an minimal example, suppose I want to list the ...
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Impact of additional int field as primary key

Directly to the point, at one time I have a table like this: create table item( item_id varchar(50), constraint pk_item1 primary key (item_id) } However from my discussion one day, there is ...
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1answer
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MySQL, temporary on disk table on primary key retrieval?

MySQL 5.5.24, Windows 7 64-bit. I've InnoDB table with primary key defined on three columns: CREATE TABLE `common_descriptions` ( `object_id` mediumint(8) unsigned NOT NULL DEFAULT '0', ...
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Table design for departments with duplicate department numbers

How should I define a database table for my company's departments where we have a set of duplicate department numbers used by an upper management tier. dept_id dept_name manager_id ...
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1answer
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How to set up multiple fields as primary key in MySQL?

I have a table with fields EmployeeID blahblah blahblah2 ..... RecordMonth RecodrdYear so each employee should only have a matching entry for a month, year, Emp#. How do I set up a table. ...
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MySQL Subquery returns more than one row

I have a table namely tbl_plays. It has the following columns and data id(PK)| gameid | drawid | etc ---------------------------------------------- 1 | 1509 | 73 | ...
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Auto Increment Primary ID inserting random values

Today I was asked to look into this problem and I have never seen anything like this before. A table in our MySQL database, with a primary IDs column, which is set to autoincrement int, had some weird ...
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Should I replace my varchar primary key with an integer primary key?

I have a table that has a varchar primary key that's associated with "Base Product Codes". They rarely change, and if they do, it's usually just being deleted or added. I figured it would be better ...
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Keys of a relation

I got relation: R = { (ABCDEF) , (A B F -> C, B C -> F, F -> A, F -> B, D E -> E, E -> D)} keys of this relation are: {BCE}, {EF} But i dont get it... why? Why not only {EF}.. it got less ...
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Autoincrement primary key in CREATE TABLE … AS SELECT

I created table using a complicated select query via CREATE TABLE ... AS SELECT.... How can I add an autoincrement primary key in this query? For example: create table `user_mv` select ...
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Overcoming the HDD IOPS limits on a billion row table? Is getting SSD the only solution?

I have a table with this structure: CREATE TABLE `requests` ( `userid` int(11) NOT NULL, `messageid` int(11) NOT NULL, `queueid` int(11) NOT NULL AUTO_INCREMENT, `problem_id` int(3) NOT NULL, ...
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Guid vs INT - Which is better as a primary key?

I've being reading around reasons to use or not Guid and int. int is smaller, faster, easy to remember, keeps a chronological sequence. And as for Guid, the only advantage I found is that it is ...
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How can I manage Primary Key length limit of 900 bytes when using hirarchyid 2 columns?

I have to define a Primary key on a table which has following 4 columns and its data types. GSiteID hirarchyid,, SiteID varchar(10), GComID hirarchyid, ComID nvarchar(10) As we know there is limit ...
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Primary Key Question

Building a database on Access 2007 and having trouble selecting the primary key. The tables consists of a student table and another table where the students are checked in. I would have liked to make ...
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How to retrieve pkey value in mysql/python on duplicate key update

I'm currently using _mysql library in python. it uses pkey(int, auto increment) value that's created when inserting data using function conn.insert_id() This is how the query is made. INSERT INTO ...
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Why should I create an ID column when I can use others as key fields? [duplicate]

Possible Duplicate: Why use an int as a lookup table's primary key? So far, I'm accustomed to creating an ID column for every table and it is practical in a way that it makes me not ...
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Normalization: 'zip code' as a primary key

I've seen frequently that you should not have all address fields (zip, street, city, state, country, etc) in the same table as your user info table (pk_id, name, email... ). This would be in ...
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Need for indexes on foreign keys

I'm struggling with indexes, primary keys and foreign keys... And the need of having them all. If I have two tables, both of them have an integer as a primary key. The first table references ...
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How do I find all tables in a DB that have no explicit primary key?

A Google search spewed forth millions of hits on how to find tables without clustered indexed, the PK normally being the clustered index of a table. However, a table could easily have a natural key as ...
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Implementing foreign keys on generalized data model

Suppose the ASCII tree below is a UML generalized concept model. To represent these entities/classes in UML, lets assume [mammal] a super class, and the level 1 classes, [wild] and [domestic] are sub ...
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MySQL auto_increment delivers different primary key in MyISAM and InnoDB

I have a table with auto incremental primary key. If I want to change a row and add new rows I got different primary keys depending on engine MyISAM and InnoDB. The original table is: pk.. ...
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553 views

Candidate key = Key = Minimal Superkey?

I got a little confused by all these keys. As I understand A key of a relational schema = The minimal subset of a superkey that is still a key = A candidate key Is this correct or not?
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Performance of primary key IDs with gaps (but in sequential order)

I know that having non-sequential IDs is bad for index performance. But assuming all my IDs are created in correct order, but with large gaps: i.e: 154300000 283700000 351300000 464200000 ...will ...
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MySQL - Autoincrement does not increment sequentally if last row was deleted

I have a table which contains an auto incremented primary key id. If I delete the last row (highest id, for exampe id = 6) and insert a new row, the new id starts at 7. Which paramater I have to ...
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2answers
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best approach to keys, if data from separate DBs to be presented in same UI

Suppose we are creating databases containing information about monkeys, and a user interface to present monkey information to users. We have two separate databases. The schemas are identical (and are ...
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Composite Primary Key efficiency as a Foreign Key

I have a table with a Composite Primary key (consisting of 4 columns) which is used to ensure no duplicates are entered into the table. I am now in need of a new table which will need to reference the ...
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How to arrange rows selected in MYSQL query?

I'm fetching data from a table "TABLE_A", it's having Primary Key as "PK_ONE" (which is unsigned INT) . I'm fetching data from "TABLE_A" with where clause on PK_ONE ; Ex: SELECT PK_ONE from TABLE_A ...
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Sharing a single primary key sequence across a database?

Is it an acceptable practice to use a single sequence as a primary key across all tables (instead of a primary key being unique for a given table, it is unique for all tables)? If so, is it ...
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MySQL looking up more rows than needed (indexing issue)

In our MySQL 5.5 database, we have following InnoDB table with 30M+ rows: +----------------+-------------+-----------------+--------+ | participant_id | question_id | given_answer_id | status | ...
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1answer
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Use surrogate or natural PK if a row is uniquely identified by two or more columns?

I am having a hard time choosing between natural and surrogate PK for my database table. The database is for a ranking system for an MOBA game. Here is more or less what I would do if I were to go ...
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Does the order of columns in a PK index matter?

I have a few very large tables with the same basic strucure. Each one has a RowNumber (bigint) and DataDate (date) column. Data is loaded using SQLBulkImport every night, and no "new" data is ever ...