Primary Key :-
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A primary key is a single field or combination of fields that uniquely identifies a row in the table.
The following are rules that make a column a primary key:
- A primary key column cannot contain a NULL value
- A primary key value must be unique within the entire table
- A primary key value should not be changed over time
Foreign Key :-
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A foreign key means that values in one table must also appear in another table.
The referenced table is called the parent table while the table with the foreign key is called the child table.
The foreign key in the child table will generally reference a primary key in the parent table.
Natural Key and Surrogate Key:-
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Sometimes the primary key is made up of real data and these are normally referred to as natural keys, while other times the key is generated when a new record is inserted into a table. When a primary key is generated at runtime, it is called a surrogate key.
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. A natural key is a column value that has a relationship with the rest of the column values in a given data record.
keys that don’t have a natural relationship with the rest of the columns in a table. The surrogate key is just a value that is generated and then stored with the rest of the columns in a record. The key value is typically generated at run time right before the record is inserted into a table.
---------------
A primary key is a single field or combination of fields that uniquely identifies a row in the table.
The following are rules that make a column a primary key:
- A primary key column cannot contain a NULL value
- A primary key value must be unique within the entire table
- A primary key value should not be changed over time
Foreign Key :-
---------------
A foreign key means that values in one table must also appear in another table.
The referenced table is called the parent table while the table with the foreign key is called the child table.
The foreign key in the child table will generally reference a primary key in the parent table.
Natural Key and Surrogate Key:-
------------------------------------
Sometimes the primary key is made up of real data and these are normally referred to as natural keys, while other times the key is generated when a new record is inserted into a table. When a primary key is generated at runtime, it is called a surrogate key.
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. A natural key is a column value that has a relationship with the rest of the column values in a given data record.
keys that don’t have a natural relationship with the rest of the columns in a table. The surrogate key is just a value that is generated and then stored with the rest of the columns in a record. The key value is typically generated at run time right before the record is inserted into a table.
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