# Database-MySQL [3i Infotech Placement]: Sample Questions 124 - 125 of 162

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## Question 124

MySQL

### Explanation

- A decomposition of a relation R into is dependency preserving decomposition with respect to the set of functional dependencies F that hold on R only if the following is hold:
Where,

- Sets of functional dependencies of relations .

- Closure of union of all sets of functional dependencies.

- Closure of set of functional dependency

- If the closure of set of functional dependencies of individual relations are equal to the set of functional dependencies of the main relation R, then we would say the decomposition D is lossless dependency preserving decomposition.

- Example:
Decomposition of

Does this decomposition preserve the given dependencies?

- Solution:

In the following dependencies hold:

In the following dependencies hold:

In all the original dependencies occur,

So, this decomposition preserves dependencies.

## Question 125

MySQL

### Explanation

- A functional dependency (FD) on a relation schema R is a constraint X ⇾ Y, where X and Y are subsets of attributes of R.
- An FD is a relationship between an attribute “Y” and a determinant (1 or more other attributes) “X” such that for a given value of a determinant the value of the attribute is uniquely defined.
- X is a determinant
- X determines Y
- Y is functionally dependent on X
- X Y
- X Y is trivial if Y X