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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Almost sequential GUIDs vs random GUIDs?

I'm looking at using GUIDs (UUID) as primary key with clustered index in SQL Server. In my webb-app I have many clients who will create items client side in javascript and save them only now and ...
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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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667 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 ...
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170 views

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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84 views

If A and B are candidate keys, then AB is candidate key or not ?

If R{abc} is a relation, f{ a->b b->a a->c b->c }, then a and b are candidate keys. What about ab ? Is it a candidate key or is it a super key or both ?
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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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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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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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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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156 views

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, ...
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2k views

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 ...
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799 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 ...
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Superkeys of this relation

I am trying to find the superkeys of this relation, but I am having troubles finding out how many superkeys there are and exactly what they are. I figured out that the candidate keys were ...
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73 views

Storing URLs in a database

I am thinking about storing URL's in my database, but I am not sure whether the way I use is an efficient way to do things or not. Table name : url url_id (Primary Key & Auto Increment) url_value ...
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817 views

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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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 ...
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2k views

Is it recommended to use Identity as an alternative to primary key?

We can declare an Identity like id_num so that id_num will have an increment of unique numbers. CREATE TABLE new_employees ( id_num int IDENTITY(1,1), fname varchar (20), minit char(1), lname ...
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538 views

NVARCHAR column as PRIMARY KEY or as UNIQUE column

I'm developing a SQL Server 2012 database and I have a doubt about nvarchar columns as primary keys. I have this table: CREATE TABLE [dbo].[CODES] ( [ID_CODE] [bigint] IDENTITY(1,1) NOT NULL, ...
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159 views

How do I create a rule for a Primary Key

I am using SQL Server 2005 and I need to create a primary key with an alpha character and 3 numbers together: p001 b201 I know I need to create a rule and bind that rule to the primary ...
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3answers
659 views

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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6k views

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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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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does last_insert_id() returns correct result when writes from multiple sessions?

I have a table in which there is a combination of 4 columns that will act as a unique key. Instead of using a composite primary key, I want to keep an id column as the primary key. This field is on ...
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152 views

Is it require to fill all tables inside of the database?

Now,I created upper that table and in order to test I will give 3 textboxes values as below. SqlCommand cmd = new SqlCommand ("Insert Into dbo.PrnInf(PrnName, PrnSurName, PrnEgn ) Values ...
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238 views

PostgreSQL SELECT primary key as “serial” or “bigserial”

I've meshed together a way to determine what the data_type is as in the data_type you use in the syntax when creating a new table based off of the PostgreSQL wiki page. If there is something wrong ...
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What and How is the ID antipattern?

What is the ID antipattern and why / under which circumstances is it considered an antipattern? The id antipattern is having a unique ID column in each table. The ID is generated for each new ...
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80 views

Shorthand for on primary key?

Is there a shorthand for merging rows based on the primary key? For example: MERGE INTO [MyDatabase].[MySchema].[MyTable] AS target USING [MyLinkedServer].[MyDatabase].[MySchema].[MyTable] AS source ...
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90 views

What Columns to create Indexes on?

I have a table , which contains upto 20 columns. The data is selected, inserted, and deleted by 3 columns: Username, StartDate, and EndDate. These 3 columns are NOT unique. The table is a ...
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does the mere existence of a primary key increase query speed for large data sets?

So, I have a table with about 2.4M rows and ~30 columns. There is no unique column within the data. The data is transaction logs from stores where each transaction number is only unique on a per store ...
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193 views

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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78 views

When do you add your foreign keys?

I'm scripting out a fairly simple database so I can simply hand off a script to someone else for an application to use. I'm curious about where best practice/the community stand on this: When should ...
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180 views

Multiple primary keys

I am new to database design and have been looking at some example data models here. One thing I don't understand is if you have a table like client_addresses from the link above: ...
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28 views

Need advice on Primary and Clustering Keys of a table

I need advise on a table which is part of a development project I'm involved. A brief summary on the use of the table: Data from multiple databases will be consolidated in this table for the purpose ...
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3answers
127 views

Copy table with separate sequences for serial columns

While creating a column management tool I came across the need to quickly replicate tables in PostgreSQL so I would not test new tools with non-test tables. To effectively test the new column tool ...
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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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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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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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serial field issue

Q: I use a serial as a datatype for my primary keys in my tables. I insert a lot of data then truncate these data one after one many times to test the data entry. My question is: Is there any ...
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78 views

“Transitive” keys

I have a central table, A, which will have a key that I'll call A_ID. Now, I have a table B in a "one to many" relationship with A (many B's map to one A). Each link will, of course, have a link ...
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Relationship with a table without unique/primary key

I have a database with 3 tables. Table Work, with a field named workName. Table SubWorks, which have a field subWorkName and work with a relationship with Work.workName. And table Activity with ...
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377 views

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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180 views

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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282 views

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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1answer
260 views

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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123 views

Relations, dependencies and normal form

I have some issues in understanding about relations and dependencies. I will show two examples and what I want to know: Assume the relation GTX {G,T,X} with the following dependencies: G,X -> T ...
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Is there a way to extract a report of or script all of the primary keys in a database?

I have just discovered that deployed copies of one of our databases have no primary keys. This is probably the fault of the SSMS Import/Export wizard, which has done the same to me. Our master copy of ...
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709 views

Missing PK/FK after database migration

We recently had a server migration. A new server is now the PROD server, and what used to be the PROD server is now the staging environment. Apparently, the data was transferred correctly, but the ...
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690 views

How to alter primary key constraint for 2 columns in same table in SQL Server?

In SQL Server, I already created a table called tblDatabase with some columns. I want to add a primary key on the two columns DatabaseName and Servername. I tried to add: ALTER TABLE tblDatabase ...
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950 views

DynamoDB: searching with primary key or range key, which way is faster?

To those familiar with DynamoDB, I'm trying to make a table where items only have 2 entries. For example, . Most of the time I'll be searching the user_id with a facebook_id on hand. Amazon's ...