Database-MySQL [3i Infotech Placement]: Sample Questions 122 - 123 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 122

Edit

Appeared in Year: 2006

Describe in Detail

Essay▾

What is the difference between Primary Key and Aggregate Key?

Explanation

Difference between Primary Key and Aggregate Key
Primary KeyAggregate Key
The column which is used for the unique identification of a record from a table is called the primary keyAggregate functions return a single result row based on groups of rows, rather than on single rows
It must contain a unique value for each row of data.They are commonly used with the GROUP BY clause in a SELECT statement, where Oracle Database divides the rows of a queried table or view into groups
It cannot contain null values.It can contain NULL value
A primary key is either an existing table column or a column that is specifically generated by the database accordingly to a define aequence.All database management and spreadsheet systems support a set of aggregate functions that can operate on a set of selected records or cells.

Question 123

Edit

Write in Short

Short Answer▾

How is the data structure of System R different from the relational structure?

Explanation

Unlike Relational systems in System R

  • Domains are not supported
  • Enforcement of candidate key uniqueness is optional
  • Enforcement of entity integrity is optional
  • Referential integrity is not enforced

Developed by: