A set of zero, one or more attributes, the value(s) of which are guaranteed to be unique for each tuple (row) in a relation.

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2
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1answer
89 views

Multi-row uniqueness constraint, checking a field has one of two values

I'd like to enforce that only one row in a database matches value A in column 1, and either value B or value C in column 2. A small example create table builders ( id text serial ); create table ...
3
votes
3answers
567 views

How does unique key help to improve SQL query performance?

Suppose I have a table with an id column and and I am maintaining unique values manually while inserting and updating records instead of creating a unique key on that column (e.g. by using a date ...
1
vote
1answer
148 views

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 ...
1
vote
0answers
25 views

Can I populate a table in mysql without ending up with duplicated entries [migrated]

I have a database. However whenever I am trying to add products to the cart table from a shopping page, I realize that the same item is added multiple times to the table if the add button for that ...
0
votes
1answer
31 views

auto_increment incremented on non-affecting queries

When performing the following query on 'sessions': INSERT IGNORE INTO sessions (user_id, archived) VALUES (3, 0) while: CREATE TABLE `sessions` ( `id` bigint(20) unsigned NOT NULL ...
1
vote
1answer
37 views

Percona MySQL 5.6 databases ignoring key length at constrait creation

We have a 3 servers running Percona MySQL 5.6 in a Master/Master configuration that are all reporting errors on key length, either too long or not specified. The structure of the databases is all ...
2
votes
0answers
63 views

Unique Index much bigger than the table itself

Pg 9.3 on debian 7. I have a very huge table in rows, about 178 million (will turn 250 million in a week and then grow 500 thousand a day), but not that huge in size, wich is 20GB, it's a small ...
0
votes
1answer
25 views

Clustering a heap by date in stead of unique composite key

I've been working on improving the performance of a large reporting database. This database is 2TB in size, and one of the larger tables is a heap with three non-clustered indexes on it. The ...
2
votes
2answers
63 views

Unique across tables

I have a table containing users. Each user has a primary email and a flag indicating if the user is deleted or not (we never hard-delete users). However, each user can also have additional emails. ...
7
votes
3answers
5k views

Differences between “Unique Key” and “Primary Key”

What are the major differences between Unique Key and Primary Key in MySQL?
0
votes
1answer
55 views

Why does InnoDB allow a 772 byte unique constraint?

I've defined a unique constraint for two columns: A bigint and a VARCHAR(256) COLLATE utf8mb4_unicode_ci Then this error occured (which I'm already familiar with): Specified key was too long; max ...
0
votes
1answer
30 views

SQL Server unique index, per subset of data, based on values of another column

Say I have a Customers table, and an Emails table. Emails table has these fields: Id CustomerId EmailValue Now, I want to create a constraint so that no duplicate emails should be ...
-1
votes
2answers
74 views

Question about choosing primary key

My scenario is that I have a super type named PERSON and two sub types EMPLOYEE and CUSTOMER. I use the Primary key from PERSON, PersonID, in both EMPLOYEE and CUSTOMER as foreign keys. However, I ...
2
votes
1answer
1k views

Mysql 5.5.38 ERROR 1062 (23000): Duplicate entry '' for key 'anykey'

I dropped my UNIQUE KEY index 'myindex' on a table and I wanted to change the UNIQUE KEY to something else, so after dropping it I did: alter table mytable add unique key anykey (add1, city, state); ...
0
votes
1answer
43 views

set unique key checks 0 in mydql

In a table i have unique value check for the combination of box_number,price,start_val,end_val so there can not be a two box number with same number which have same price , start_val and end_val.. ...
0
votes
1answer
23 views

Records in a table unique period

I have the following table: +--+---------+-------+--------------+--------------+ |ID|HEADER_ID|VERSION|FROM_DATE_TIME| TO_DATE_TIME| +--+---------+-------+--------------+--------------+ | 1| ...
5
votes
2answers
198 views

Managing CTE execution order under uncertainty

I am writing a large, multi-step CTE for performance reasons. In one query, data must be moved from one table to another, but the quantity of rows moved is uncertain and could be zero. In a ...
2
votes
1answer
272 views

Foreign Key NULL vs Foreign Key to an empty string

This is a table for a catalog of medicines. Some have a pharmaceutical brand, others are generic (i.e. they will never have brand information) CREATE TABLE medicine ( id serial PRIMARY KEY, ...
1
vote
2answers
103 views

Is unique index better than unique constraint when an index with an operator class is required

Postgres docs say: The use of indexes to enforce unique constraints could be considered an implementation detail that should not be accessed directly. One should, however, be aware that there's ...
27
votes
3answers
21k views

PostgreSQL multi-column unique constraint and NULL values

I have a table like the following: create table my_table ( id int8 not null, id_A int8 not null, id_B int8 not null, id_C int8 null, constraint pk_my_table primary key (id), ...
0
votes
1answer
121 views

MySQL performance of applying unique constraint single column vs combination column

I have a large MySQL InnoDB table containing around 137 million rows. I need to add a unique constraint to the table. We have two options: 1) A combination index on three columns, one of which will ...
8
votes
3answers
1k views

Email address unique or primary key?

I am a newbie in databases. I read around and found out that it's probably not a great idea to use email address as primary key because string comparisons are slower which effects performance in ...
1
vote
1answer
164 views

Merge Problems SQL Server

I'm trying to create a procedure that will take the values from a temporary table, and load them into another table. The second table has a composite unique constraint across its three columns (Not ...
1
vote
1answer
127 views

MySql - unique key not working

I have the following table: CREATE TABLE `timeline_lists` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(11) NOT NULL, `list_type` int(11) NOT NULL, `s_object_id` int(11) NOT NULL ...
0
votes
4answers
109 views

SqlServer: can one table's PK be the FK of other two table's? [duplicate]

I have three tables project, users and proj_user. The PK of proj_user table is the FK of project and users table's pk e.g.(project_id,user_id) My question is, is it possible for the project_id and ...
1
vote
0answers
41 views

Combining fields to make a unique record or keeping them separated

I've been asked to implement what has before, been a bunch of CSV files, into a MySQL database. I'm at a point in the design where all the schemas, tables and fields have been mocked-up; however I'm ...
1
vote
1answer
134 views

Unique constraint to enforce max one null per item

I am using PostgreSQL 9.3. Suppose we are manufacturing some items of certain types, at any moment we are producing at most one item of a certain type. The following table captures our history of ...
0
votes
1answer
83 views

Is it possible to have a unique key condition based on another value?

I have a table with the following columns: ID, STRING_VALUE, ENUM_VALUE, CATEGORY_IDENTIFIER I'd like to create a condition that won't allow two identical ENUM_VALUEs, but only if their ID is also ...
2
votes
2answers
52 views

Strategy to find the unique bivariate polynomials

I have table that stores Tutte polynomials of a large set of graphs. These are bivariate polynomials with integer coefficients. An example of a polynomial taken from Wikipedia is: Since the ...
0
votes
1answer
86 views

Creating unique constraint to be validated from input

I have this table name tbl with this table definition: create table tbl ( id serial primary key not null, counter integer not null default 1, ref_id integer not null, date_booked date ...
0
votes
1answer
45 views

“key violation” when trying to import data into MS Access

I am trying to import data into an MS Access table from a flat ASCII file. I've done this many times before but now I am getting a "key violation." There is only one key in the table and it's an ...
1
vote
0answers
32 views

Clarify unique constraint and index, cannot grasp the concepts to 100% [duplicate]

When reading about UNIQUE, I understand the concept but when it comes to the practical part of it, I get confused and I'm unsure of what it means. What I do understand, is that there are two ways to ...
1
vote
2answers
136 views

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 ...
0
votes
2answers
73 views

Should I create a multi-column UNIQUE index?

I have created the following MySQL table, which stores which sections of our site a user visited (and the Count of visits): CREATE TABLE `Visits` ( `ID` int(10) unsigned NOT NULL AUTO_INCREMENT, ...
50
votes
5answers
16k views

When should I use a unique constraint instead of a unique index?

When I want a column to have distinct values, I can either use a constraint create table t1( id int primary key, code varchar(10) unique NULL ); go or I can use a unique index create table t2( id ...
0
votes
0answers
22 views

Should a surrogate key reflect one of my columns? [duplicate]

I currently have a column called LoadID which is a surrogate key that just increment by max()+1. I also have LoadNumber which always seems to have the exact same value of LoadID, since they will ...
1
vote
0answers
29 views

Preventing unique key constraint violation when pre-existing row has 'expired' [duplicate]

I have the following table schema; CREATE TABLE LOCKS ( lock_uid INTEGER NOT NULL, file_uid VARCHAR2(32 char) NOT NULL UNIQUE, owner VARCHAR2(255 char) NOT NULL, expires DATE NOT ...
1
vote
1answer
96 views

How to find the length of multiple column index in MySQL

Is there a way to find out what is the length in bytes for the unique index (NKU) key created through the following command: CREATE TABLE test_ ( testId bigint(20) NOT NULL, name varchar(75) ...
1
vote
1answer
29 views

Duplicate Data from two column

i have a table which has only two column one is pid(Photo ID) and another one is tid(Tag ID) +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
2
votes
2answers
2k views

Optimized query to fetch a record from 10 million entries

A table has 2 fields | UniqueKey | TimeStamp | ------------------------- | xfsddddq | 1024125412 | | xfstttdx | 1024125413 |< | xfsdxxau | 1024125415 | Estimated, there are 10 million ...
5
votes
1answer
411 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: ...
1
vote
1answer
57 views

What problem prevents well defined behavior of a foreign key on a non-unique column?

In my noob opinion, it strikes me that in a serialized environment, this shouldn't be a problem. Is that correct? If not, please explain to me why a foreign key's behavior on a non-unique column is ...
4
votes
1answer
2k views

When changing the size of a nvarchar column, do I need to drop the unique index? And will the table get locked when recreating the index?

In our database a big table exists that more or less looks like this: CREATE TABLE dbo.production_data ( pd_id BIGINT PRIMARY KEY, serial NVARCHAR(16) NOT NULL UNIQUE, ... ); but now ...
4
votes
2answers
370 views

How can I enforce ensure uniqueness of an association with a time dimension?

I have a database table AB which tracks the association of A and B over time: create table AB columns ( ARef ..., -- FK of A BRef ..., -- FK of B Since as Timestamp, Until as Timestamp, ...
2
votes
1answer
159 views

Does a SQL server unique constraint partially or fully fail a multi-row write?

If some rows of a writing query fails a unique constraint, will only those writes be rejected, or will the entire query fail?
2
votes
1answer
278 views

NEWSEQUENTIALID() resets sequence on server restart

MSDN learns me that NEWSEQUENTIALID(): Creates a GUID that is greater than any GUID previously generated by this function on a specified computer since Windows was started. After restarting ...
1
vote
1answer
184 views

Unique constraint on multiple nullable columns Sql Server

We have a PriceCombo table with the following columns: id (not null), a_id(null),b_id(null),c_id(null), discount(not null). We are using this table to figure out which price to assign various combos ...
2
votes
1answer
151 views

ER relation with unique key

I've a problem about my ER diagram. Assume that I want to draw a diagram with student, member and team. Here is my specs: A student does not have to be a member of any team. A student could be a ...
1
vote
1answer
2k views

Duplicate key violates unique constraint

When I use this query everything is fine: UPDATE users SET f_name='Mike', l_name='MyLastName', username='blabla', "password"='asdfsdaf', "class"=12, ...
1
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0answers
35 views

table scheme definiation it this way that insert duplicate into another table

I have a table in which there is a column name with SP varchar(10) NOT NULL. I want that column always to be unique so i created unique index on that column . My table schema as follows : CREATE ...