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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How does SQL Server choose an index key for a foreign key reference?

I am working with a legacy database that was imported from MS Access. There are about twenty tables with non-clustered, unique primary keys that were created during the MS Access > SQL Server upgrade. ...
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PostgreSQL: Corrupt primary key, inconsistent table

While recovering from a cloud failure, I found that some tables on a PostgreSQL database are behaving strangely. These tables are indexed using a primary key, but a pg_dump yielded duplicate fields, ...
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Primary Key Type's Effect on Performance in Oracle?

In MS SQL Server, it is well documented that the type of the primary key can have a dramatic effect on performance. Using narrower types and sequential values significantly improves insert performance ...
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PRIMARY KEY CONSTRAINT fundamentals

Can you explain why "primary key constraint" exists if, as you know, it is possible to create relationships between tables using unique indexes only ? The RDBMS that is used is SQL Server. In fact, ...
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395 views

Surrogate key / Primary key: Better to use an existing unique data field or create a key field?

I am not sure if this question has been asked or not. At least I couldn't find it. I am curious about a primary key in terms of efficiency with data searching and retrieval. This is a hypothetical ...
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SQL table design for primary keys (best practice)

I have a User table that contains the following fields ID (Auto-generated GUID) UserName Password FirstName LastName Email AddressID (GUID) This is linked to the table Address (1-1 relation) which ...
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5answers
481 views

Using Timestamp plus Integer as Primary Key

In Sql Server, what would the drawbacks and disadvantages be of using a primary key that is: Two Character Table Identifier + YEAR + MONTH + DAY + HOUR + MINUTE + MILLISECOND + random integer between ...
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2answers
501 views

checksum(newid()) as primary key - what happens if a collision occurs?

Inspecting a rather critical database that is used by some software on my system, I found that one of the tables had a primary key on the column Id, where Id is calculated using checksum(newid()). ...
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575 views

Index Key Column Order

I have created a joining table for many-to-many relationship. The table only has 2 cols in it, ticketid and groupid typical data would be groupid ticketid 20 56 20 87 20 ...
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Optimised Schema for City-to-City Distance Table

This is my first question, forgive me if this question is simple. I'm stuck here, trying to implement the relations for the data represented below. I want to scale it vertically (new rows), instead of ...
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1answer
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Is there any performance difference in using a unique index on primary key?

I know there are lost of similar questions to this one, but none that really answers this: Is there ANY difference in performance in using an unique index in a primary key, using a MyISAM table on a ...
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Postgres primary key sorted in the reverse order. Will it use the index efficiently?

My Rails database is backed by Postgres database. As you may know, each table in Rails gets assigned a primary key which is of Integer type and is indexed. My list views show records in the reverse ...
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“on duplicate key update” all the non-key fields mentioned in the insert

How can I update the field values mentioned in the insert portion without listing them again in the on duplicate key update portion? insert into tablename set keyname = 'keyvalue', fieldname = ...
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Is index_type ignored on MySQL primary keys in create table?

I have seen a create table whose primary key had an identifier where it should have an index_type, something like that: create table a (foo INTEGER, PRIMARY KEY foo_id (foo)); The thing is that ...
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1answer
463 views

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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MySQL - Normalization over meaningless data - Compound Primay Keys or Surrogate ID field

Please forgive my title; if you have a suggestion for it, feel free to comment. I have a database: DROP TABLE IF EXISTS `books`; CREATE TABLE `books` ( `isbn` VARCHAR(255) NOT NULL, `title` ...
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3answers
465 views

File name as primary key?

I have a few tables I'm going to create for a website, Literature, video, and image. Is there a good reason why I shouldn't use the file name as a primary key. For instance... "someimage.png" as the ...
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2answers
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Generalisation in databases

I am working on a Hospital Management project in DB2. I have one table for staff with a primary key of staff_id. The hospital has to have different staff... e.g doctors,nurses,e.t.c. Is it better to ...
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How can an identity primary key index become fragmented?

From what I understand about index fragmentation, this should not be possible. The cases I have found in my databases are non-clustered. Example: ALTER TABLE [dbo].[ClaimLineInstitutional] ADD ...
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4answers
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Two-sided UNIQUE INDEX for two columns

Creating a table with composite PRIMARY KEY or using UNIQUE INDEX for two columns guarantee uniqueness of col1, col2. Is there a tricky approach to make the reverse order of two columns UNIQUE too ...
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IDENTITY_INSERT is set to OFF?

Here is my script of my db , CREATE TABLE [dbo].[MyTable]( [ID] [int] IDENTITY(1,1) NOT NULL, [Code] [nvarchar](25) NULL, [Name] [nvarchar](25) NULL, [dob] [date] NULL , CONSTRAINT [PK_MyTable] ...
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How is INDEX on Composite Primary Key in mysql?

When making a composite primary key for two or more columns, e.g. PRIMARY KEY(col1, col2, col3); will the system INDEX each column individually? The reason that I am asking this question is that when ...
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size of a primary key and foreign key

Do a primary key and a foreign key referencing it must have the same column size in sql server 2008 ? could someone indicate me a link to a documentation explaining this ? Thank you for help.
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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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2answers
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What is the advantage of using numeric primary keys in a relational database?

Many tables in a relational database system (in my admittedly limited experience) have this sort of structure (Oracle syntax as that's what I'm used to): create table widgets ( widget_id number ...
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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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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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Why would i get a duplicate write error of auto-generated primary key?

Hi I'm not a DBA so forgive my ignorance. I don't have access to administrator tools etc. However, I do know that we have a live server which is approaching capacity ie 80%-90% full perhaps. What is ...
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3answers
501 views

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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1answer
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Can I use a Clob as a table key (from Java)?

Following a suggestion made to another question to store large amounts of text: can one use a CLOB as primary key field (i.e., from Java's DataNucleus implementation of JDO)? I know it is probably a ...
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2answers
3k views

Single Identity column and composite key, which to make primary?

I've got a table that's a working copy subset of a base table. The base table has a composite key with a clustered index. However I need a single column unique identifier for my framework to work ...
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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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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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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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Does the MySQL primary key affect the efficiency of a SELECT query?

Does the primary key serve any purposes apart from uniquely identifying a specific row? For example, a table with an autoincremented primary INT key could greatly aid in search due to the option of ...
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3answers
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performance of multi field primary key or 'contrived' 'semi artificial' key

This is not a question regarding the benefits or otherwise of using an artificial auto increment key in any given table against using a multi-field 'primary key'. That discussion (or argument) can ...
2
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1answer
586 views

Question on Design for User + User Groups + User Types + Subscriptions Model

I am redeveloping an existing web application with both weak source code and a weak underlying database design. I'm trying to develop things in a way that future expansion will be much easier, ...
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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
406 views

Does the size of the primary key contribute to table size?

I have a table (InnoDB) with data length around 36G and index length 23G. It had a composite primary key across three columns. As an initial attempt to reduce the size of this table, I dropped the ...
2
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1answer
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Validate Primary Key and Index Selection

I have a table that will store transaction data from store sales registers, I have read quite a bit on index and key choice and below is what I have concluded is the best option but I am new to this ...
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Is there a good way to select a row where the key represents the lower bound of a range?

I am designing some tables and a number of the tables have as the key a lower and upper bound which never overlap. I want to query by a value that can fall withing any of those ranges. If I keep both ...
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2answers
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Two primary keys to one foreign key

racing_couple ID (PRIMARY) breeding_couple ID (PRIMARY) egg IDpar(FOREIGN KEY) I have 2 IDs from 2 different tables (racing_couple and breeding_couple) and they are primary keys. In 3. table (egg) ...
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1answer
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prevent MySQL Workbench to add index for foreignkey constraint when it is first part of primary

I know for each foreign key we should make an index on its column, But it is not necessary when that column in first part of PRIMARY index. MySQL accepts this query: CREATE TABLE IF NOT EXISTS ...
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1answer
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NEWB Getting to KNow New Database and Understand Where Relationships Are

I'm teaching myself SQL using MYSQL and a textbook. While working through the textbook I'm using a database I'm kinda familiar with - an exported copy of my CMS driven websites database. My website ...
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2answers
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What can I do to make mysql use the expected indices?

What can I do to make mysql use the expected indices? I've got 4 tables, two containing resources, and the others containing historical changes. One pair uses indexes correctly, the other doesn't, ...
2
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1answer
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Unique insert performance: Primary Key vs Unique Index

I have a table of unique values (domains_unique), with collumn domain varchar(255), with more than 20 mil records. What's the fastest way to insert into the table, by keeping the domain unique ...
2
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1answer
601 views

SQL Server - storing ulong as primary key

I need to store ulong values as a primary key in SQL Server. Since SQL Server doesn't have a ulong datatype (or for that matter anything unsigned), the only way to go is to have column as ...
2
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1answer
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unique constraint violated (ORA-00001) in concurrent insert [closed]

I have a procedure that is called from concurrent transactions: //Some actions here INSERT INTO table1 (table1_id, table1_val1, table1_val2, table1_val3) VALUES ...
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2answers
463 views

Replacing composite key with surrogate

I have the following table that has a couple of million rows in it and is 99% fragmented virtually all of the time. My plan was to insert a IDENTITY field as a surrogate key to replace the current ...
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Why are runtimes different for a table including a primary key versus a table with a clustered unique index added after population [closed]

When I create a temporary table with a PK defined from the outset like this I get great performance in subsequent joins on that key: create table #temp ( field1 int not null field2 int ...