what is the difference between natural key composite keys and surrogate keys?
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A natural key is a column value that has a relationship with the rest of the column values in a given data record. ... A surrogate key like a natural key is a column that uniquely identifies a single record in a table. But this is where the similarity stops. Surrogate keys are similar to surrogate mothers.
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['Super Key. Super key is a set of one or more than one keys that can be used to identify a record uniquely in a table. ... ', 'Candidate Key. A Candidate Key is a set of one or more fields/columns that can identify a record uniquely in a table. ... ', 'Primary Key. ... ', 'Alternate key. ... ', 'Composite/Compound Key. ... ', 'Unique Key. ... ', 'Foreign Key.']
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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.
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3 Answers. Primary Key: Is a single field chosen by the designer to uniquely identify a record in a table (relation), cannot be null (empty/unassigned). ... Secondary (or Alternative) Key: Is any field in the table that isn't selected to be any of the two types above.
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Primary Key - is a column or group of columns in a table that uniquely identify every row in that table. Candidate Key - is a set of attributes that uniquely identify tuples in a table. Candidate Key is a super key with no repeated attributes. ... Foreign Key - is a column that creates a relationship between two tables.
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The primary key is a unique value that identifies each record. ... A natural key is a single column or set of columns that uniquely identifies a single record in a table, where the key columns are made up of real data. When I say “real data” I mean data that has meaning and occurs naturally in the world of data.
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A primary key uniquely identifies a record in the relational database table, whereas a foreign key refers to the field in a table which is the primary key of another table.
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A primary key is a special key used to uniquely identify records in a table, whereas a foreign key is used to establish relationship between two tables. Both are identical in structure but play different roles in relational database schema.
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Secondary key is a non-unique field. One secondary key value may refer to many records. Candidate Key or Alternate key A relation can have only one primary key. It may contain many fields or combination of fields that can be used as primary key.
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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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Primary key will not accept NULL values whereas Unique key can accept one NULL value. A table can have only primary key whereas there can be multiple unique key on a table. A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index.
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A primary key is a column or a set of columns that uniquely identify a row in a table. ... A foreign key is a field (or collection of fields) in a table whose value is required to match the value of the primary key for a second table. ...
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Primary Key can't accept null values. Unique key can accept only one null value. By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index. ... In SQL Server, Unique key can be made foreign key into another table.
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A primary key is a column or a set of columns that uniquely identify a row in a table. A primary key should be short, stable and simple. A foreign key is a field (or collection of fields) in a table whose value is required to match the value of the primary key for a second table. ... A table can have multiple foreign keys.
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A superkey is a set of attributes within a table whose values can be used to uniquely identify a tuple. A candidate key is a minimal set of attributes necessary to identify a tuple; this is also called a minimal superkey.
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You can only have one primary key per table, but multiple unique keys. Similarly, a primary key column doesn't accept null values, while unique key columns can contain one null value each. And finally, the primary key column has a unique clustered index while a unique key column has a unique non-clustered index.
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['NOT NULL - Ensures that a column cannot have a NULL value.', 'UNIQUE - Ensures that all values in a column are different.', 'PRIMARY KEY - A combination of a NOT NULL and UNIQUE. ... ', 'FOREIGN KEY - Uniquely identifies a row/record in another table.']