@prateek987 said:my tips for it officer..Respected guys (and girls if any)VERY VERY IMP. TOPICSNORMALIZATION ..LOCKING....FEW VERY BASIC SQL STATEMENTS...DATA COMMUNICATION...OS mein...banker algo..NOW COMING TO THE NORMAL FORMS...LETS LEARN THEM..(pakka aana hain atleast 2-3 marks)..UNF = If a table contains non-atomic values at each row, it is said to be in UNF. An atomic value is something that can not be further decomposed. A non-atomic value, as the name suggests, can be further decomposed and simplified. Consider the following table:First Normal Form (1NF)A relation is said to be in 1NF if it contains no non-atomic values and each row can provide a unique combination of values. The above table in UNF can be processed to create the following table in 1NF.Second Normal Form (2NF)A relation is said to be in 2NF f if it is already in 1NF and each and every attribute fully depends on the primary key of the relation. Speaking inversely, if a table has some attributes which is not dependant on the primary key of that table, then it is not in 2NF.Third Normal Form (3NF)A relation is said to be in 3NF, if it is already in 2NF and there exists no transitive dependency in that relation. Speaking inversely, if a table contains transitive dependency, then it is not in 3NF, and the table must be split to bring it into 3NF.What is a transitive dependency? Within a relation if we seeA → B [B depends on A] And B → C [C depends on B] Then we may derive A → C[C depends on A]Such derived dependencies hold well in most of the situations. For example if we have Roll → Marks AndMarks → GradeThen we may safely derive Roll → Grade.Boyce-Code Normal Form (BCNF)A relationship is said to be in BCNF if it is already in 3NF and the left hand side of every dependency is a candidate key. A relation which is in 3NF is almost always in BCNF. These could be same situation when a 3NF relation may not be in BCNF the following conditions are found true.The candidate keys are composite.There are more than one candidate keys in the relation.There are some common attributes in the relation.Fourth Normal Form (4NF)When attributes in a relation have multi-valued dependency, further Normalization to 4NF and 5NF are required. Let us first find out what multi-valued dependency is.A multi-valued dependency is a typical kind of dependency in which each and every attribute within a relation depends upon the other, yet none of them is a unique primary key.Fifth Normal Form (5NF)These relations still have a problem. While defining the 4NF we mentioned that all the attributes depend upon each other. While creating the two tables in the 4NF, although we have preserved the dependencies between Vendor Code and Item code in the first table and Vendor Code and Item code in the second table, we have lost the relationship between Item Code and Project No. If there were a primary key then this loss of dependency would not have occurred. In order to revive this relationship we must add a new table like the following. Please note that during the entire process of normalization, this is the only step where a new table is created by joining two attributes, rather than splitting them into separate tables.Chahe kuch bhi ho jay...just learn the above..koi confusion ho toh bataye...
Thanks Sir/Madam for this elucidation of Forms
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