what is the difference between a primary key and foreign key in a database?
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Difference between Primary Key and Foreign Key. Primary key uniquely identify a record in the table. Foreign key is a field in the table that is primary key in another table. ... By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index.
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Primary Key is a unique and non-null key which identify a record uniquely in table. A table can have only one primary key. Candidate key is also a unique key to identify a record uniquely in a table but a table can have multiple candidate keys. Primary key column value can not be null.
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Before you can ask the difference between primary key and clustered index, you have to know that a key and an index are not the same thing. A key can be a primary key or a foreign key. ... A clustered index is a special index that defines the physical order of your table (it should be a sequential data).
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Relational - it means data is organized in tables and there are several mechanisms recognized like primary key, foreign key, uniqueness, data normalization. ... Transactional database is database able to manipulate data within transactions.
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You define a foreign key with the FOREIGN KEY clause in the CREATE TABLE or ALTER TABLE statement. A foreign key makes its table dependent on another table called a parent table. ... A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values.
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When you design a database, you divide your information into tables, each of which has a primary key. You then add foreign keys to related tables that reference those primary keys. These foreign key-primary key pairings form the basis for table relationships and multi-table queries.
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Primary Key: that is used for uniquely identified a perticular row of a database table . Primary INDEX: That is used for getting a index from a database table and that indexing is done on unique based.
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The main difference between relation and relationship in DBMS is that relation refers to a table in a relational model based database while relationship refers to how two tables are connected together in a relational model based database. A database is a collection of related data.
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A primary key is a table column that serves a special purpose. Each database table needs a primary key because it ensures row-level accessibility. ... The values that compose a primary key column are unique; no two values are the same. Each table has one and only one primary key, which can consist of one or many columns.
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MySQL: MySQL is an open-source relational database management system (RDBMS). ... MySQL uses primary keys to uniquely identify each row (a.k.a record) in a table, and foreign keys to assure the referential integrity between two related tables. Oracle: Oracle is a multi-model database with a single, integrated back-end.
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Answer: The primary key is the field or combination of fields that uniquely identifies each record in a table. A foreign key is a field in a related table that is also a primary key in a primary table.
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The primary key is a unique key in your table that you choose that best uniquely identifies a record in the table. All tables should have a primary key, because if you ever need to update or delete a record you need to know how to uniquely identify it. A surrogate key is an artificially generated key.
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Primary and foreign keys are a way in which to constrain related data together to ensure data in your database remains consistent and to ensure no redundant data is in the database as a result of deleting a table or row in one table that affects data in other tables that may perhaps rely on that information.
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Primary key is used to identify data uniquely therefore two rows can't have the same primary key. It can't be null. On the other hand, foreign key is used to maintain relationship between two tables. Primary of a table act as forgein key in the other table.
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You can only have 1 primary key in a database table. ... You can have more than 1 unique key table column (unlike primary key which means only 1 table column in the table is unique). INDEX also creates uniqueness. MySQL (example) will create a indexing table for the column that is indexed.
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A relational databases relies on the relational model, on the other hand a object database relies on the OOP. ... The difference between relational database and object oriented database is that the relational data base stores data in the form of tables which contains rows and columns.
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In MySQL, a primary key is a single field or combination of fields that uniquely defines a record. None of the fields that are part of the primary key can contain a NULL value. A table can have only one primary key.