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प्रश्न
Differentiate Unique and Primary Key constraint.
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उत्तर
| Unique Key Constraint | Primary Key Constraint |
| The constraint ensures that no two rows have the same value in the specified columns. | This constraint declares a field as a Primary Key which helps to uniquely identify a record. |
| The UNIQUE constraint can be applied only to fields that have also been declared as NOT NULL. | The Primary Key does not allow NULL values and therefore a field declared as Primary Key must have the NOT NULL constraint. |
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संबंधित प्रश्न
The command to delete a table is ______
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| EMP CODE | NAME | DESIG | PAY | ALLO WANCE |
| S1001 | Hariharan | Supervisor | 29000 | 12000 |
| P1002 | Shaji | Operator | 10000 | 5500 |
| P1003 | Prasad | Operator | 12000 | 6500 |
| C1004 | Manjima | Clerk | 8000 | 4500 |
| M1005 | Ratheesh | Mechanic | 20000 | 7000 |
To display the details of all employees in descending order of pay.
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| EMP CODE | NAME | DESIG | PAY | ALLO WANCE |
| S1001 | Hariharan | Supervisor | 29000 | 12000 |
| P1002 | Shaji | Operator | 10000 | 5500 |
| P1003 | Prasad | Operator | 12000 | 6500 |
| C1004 | Manjima | Clerk | 8000 | 4500 |
| M1005 | Ratheesh | Mechanic | 20000 | 7000 |
To remove the employees who are mechanics.
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Construct the following SQL statement in the student table-
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Construct the following SQL statement in the student table-
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