| KEY NAMES |
KEY DESCRIPTION |
| PRIMARY KEY |
Name of the column which uniquely identifies each row of the table with no null value in any row of the table. |
| UNIQUE KEY |
Name of the column which uniquely identifies each row of the table, but it can accept a null value for any row of the table. |
| COMPOSITE KEY |
The combination of two or more column representing as a unique for each row of the table after merging the columns. It acts like a single column in contest of the key. |
| SURROGATE KEY |
A key which has no buisness logic or which have no existance in the real world. for more clarity see NATURAL KEY |
| FOREIGN KEY |
Name of the column which have the reference of the other table by having the same value of any column other table. |
| CANDIDATE KEY |
Any key which can represent as unique for each row is called CANDIDATE KEY. Hence PRIMARY KEY, UNIQUE KEY and COMPOSITE KEY are a member of CANDIDATE KEY |
| NATURAL KEY |
A key which have a real existinence in business logic or have the real value in the world like AADHAR NO in India and SSN NO in USA |
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