SQL - Unique Key, Primary Key & Foreign Key - Stack Overflow
Apr 25, 2015 · What are the differences between Unique Key, Primary Key and Foreign Key with respect to concept of SQL? How they are different from each other?
sql - What is the difference between primary, unique and foreign …
Nov 7, 2009 · What is the difference between primary, unique and foreign key constraints, and indexes? I work on Oracle 10g and SQL Server 2008.
sql - difference between secondary key, foreign key, and primary …
Jun 1, 2018 · Primary Key: Is a single field chosen by the designer to uniquely identify a record in a table (relation), cannot be null (empty/unassigned). Foreign Key: Is the Primary Key one …
sql - What is the difference between a primary key and a surrogate …
Apr 21, 2016 · A primary key is the identifying column or set of columns of a table. Can be surrogate key or any other unique combination of columns (for example a compound key).
What is difference between foreign key and reference key?
Dec 22, 2011 · The Reference Key is the primary key that is referenced in the other table. On the other hand, Foreign Key is how you link the second table to the primary tables Primary Key (or …
Is it fine to have foreign key as primary key? - Stack Overflow
Jun 11, 2012 · A foreign key is just a referential constraint between two tables One could argue that a primary key is necessary as the target of any foreign keys which refer to it from other …
sql - When should I use primary key or index? - Stack Overflow
May 20, 2010 · A primary key is a constraint, not an index. An index can be associated with a primary key, but it's not required. And unless using SQL Server, an index doesn't ensure …
sql - Diferença e utilização entre Primary Key e Foreign Key - Stack ...
Jan 15, 2019 · Fiz uma modelagem do banco de dados relacionando algumas tabelas e no final de tudo foi me dito que estava errado por não possuir as chaves PK e FK. A questão é, como …
sql - What is the difference between a candidate key and a …
Oct 10, 2012 · As a practical matter, the use of foreign key references without a declared primary key leads to a mess. It could be a logically correct mess, but it's a mess nonetheless. …
What is the difference between an Index and a Foreign Key?
Jan 18, 2017 · The primary key for the table is a unique index, and usually only has one column. A foreign key is a value in a table that references a unique index in another table.