Database-MySQL [3i Infotech Placement]: Sample Questions 83 - 85 of 162

Glide to success with Doorsteptutor material for competitive exams : get questions, notes, tests, video lectures and more- for all subjects of your exam.

Question 83

Edit

Describe in Detail

Essay▾

What is BCNF (Boyce-Codd Normal Form) ?

Explanation

Boyce Codd Normal Form (BCNF)
  • A relational schema R is considered to be in Boyce-Codd normal form (BCNF) if, for every one of its dependencies X ⇾ Y, one of the following conditions holds true:
    • X ⇾ Y is a trivial functional dependency (i.e.. . , Y is a subset of X)
    • X is a superkey for schema R
  • Informally the Boyce-Codd normal form is expressed as “Each attribute must represent a fact about the key, the whole key, and nothing but the key.”

Question 84

Edit

Write in Short

Short Answer▾

What is VDL (View Definition Language) ?

Explanation

  • This language is used to specify user views and their mapping to conceptual schema.
  • It defines the subset of records available to classes of users.
  • It creates virtual tables and the view appears to users like conceptual level. It specifies user interfaces.

Question 85

Edit

Describe in Detail

Essay▾

Which date function is used to find the difference between two dates?

Explanation

Brifily Define MONTH Between
  • MONTH_BETWEEN is used to find the difference between two dates.
  • Start date is put in the first cell and end date in another.
  • This function returns the number of month between date 1 and date 2.
  • When the two dates have same day component, then the return value is a whole number.
  • Return value might thus include a fraction that considers the difference in the days on 31-day month.
  • Return date is positive when the first date is later than the second date otherwise it is negative.

Return value:

NUMBER

Syntax:

MONTHS_BETWEEN (date1, date2)

Developed by: