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What are the several kinds of the update operations on relations? Also explain the constraints on these update operation. Give instance in support of your answer.
There are three primary update separation on relations: (i) Insert : It is used to insert a latest tuple or tuples in a relation. Insert can violate any of the four tuples of constraints: Domain constraints, key constraints, entity integrity and referential integrity (ii) Delete : It is used to delete tuples. The delete operation can violate just referential integrity, if the tuple being deleted is referenced through the foreign keys from other tuples in the database (iii) Modify: It is used to change value of a few attributes in existing tuples. Modify can also violate any of the four constraints as specified within insert operation.
Examples: (1) Inserting a tuple having null value for primary key violates entity integrity (2) Deleting a tuple in a table for that tuples exist other tables that are dependent on those tuples will violate referential key integrity. (3) Modifying a primary key attribute to any other such that is aheady exists in the table will violate entity integrity.
Consider the subsequent relation Professor (Pfcode, dept, head, time) It is assumed that (i) A professor can work in much more than one
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How can i turn a conceptual entity relationship diagram into a logical entity relationship diagram? what do i have to do with "mandetory or" and "optional or" relationships?
find the name of supplier who supply some red part
What are audit trails? An audit trail is a log of all alters to the database along with information like which user performed the change and when the alter was performed.
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Explain Foreign Key? Foreign Key - Let there are two relations (tables) R and S. Any candidate key of the relation R that is referred within the relation S is known as the fo
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System level permissions : With the use of data dictionary you can view them. Let us take the table name as user_sys_privs (used in oracle). DESCRIBE USER_SYS_PRI
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