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What is a foreign key, and what is it used for?
A foreign key is used to establish relationships between relations in the relational model. Technically, a foreign key is a column (or columns) appearing in one relation that is (are) the primary key of another table. Although there might be exceptions, the values in the foreign key columns usually must correspond to values existing in the set of primary key values. This correspondence necessity is created in a database using a referential integrity constraint on the foreign key.
DROP TABLE Command: When an existing object is not needed for further use, it is always better to eliminate it from the database. To remove the existing object from the databas
2NF Normal Form : A relation schema process R is in 2NF if it is in 1NF and each non-prime attribute A in R is fully functionally related on primary key. Second normal form (2N
how to write a in a text and load it on mysql
Question: Using the data model express the following queries in SQL. (a) Create the Table named "Cinema" and make the cinema_code to be the primary key of the relation and
Determine the rule that a value of a foreign key should appear as a value of some particular table is called a Ans: Referential constraint. The rule that a value of a fo
Define data model? A data model is a collection of conceptual tools for explaining data, data relationships, data semantics and consistency constraints.
Benefits and Limitations od Data Models?
Which is a legal expression in SQL? SELECT NAME FROM EMPLOYEE is a legal expression in SQL.
Types of Locks There are two necessary types of locks: Binary lock : This locking mechanism has two states for to a data item: locked or unlocked Multiple-mode loc
What are segments in oracle? Segments - Each table has single field of disk space, known as segment, set aside for it in the tablespace. Segments consist of contiguous sections
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