Sunday, March 31, 2013

NormalForms and DDL,DCL,DML,TCL commands


DDL : CREATE, ALTER, DROP

DML : INSERT, UPDATE, DELETE
DCL : GRANT, REVOKE
TCL : COMMIT, SAVE POINT, ROLLBACK
DQL : SELECT

Normalization is a process of efficiently organizing data in the database.
goles of NF: There are two goals of the normalization process: eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table).
1stNF : The first normal form (or 1NF) requires that the values in each column of a table are atomic. By atomic we mean that there are no sets of values within a column.
1NF --every row should be in atomic form....there should not be more than one value for an attribute in a row...
2NF --there should be no partial dependency. it means that there should be no dependency between part of a key to non-key. This does not happen if you choose a single attribute as your primary key.
3NF -- there should be no transitive dependecy. we can also say as there should be no Non-Key to Non-key dependency...
BCNF -- every determinant should be a candidate key.

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