Database-Oracle [3i Infotech Placement]: Sample Questions 33 - 34 of 132

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Question 33

Oracle
Edit

Statement

True-False▾

Constraints cannot be exported through Export command.

Answer

FALSE

Explanation

  • Export command can export constraints- it can specify whether table constraints should be exported with table data.
  • For import in the normal import order- referential constrains are imported only after all tables are imported.
  • This sequence prevents errors that occur when constraints can fail when data has not been fully imported.
  • When an error occurs, import generates an error message for failed row and continues importing other rows in the table.
  • Constrain export can be disabled to avoid this.

Question 34

Oracle

Question

MCQ▾

What are the types of calculated columns available?

Choices

Choice (4)

a.

Summary, Formula, & Placeholder columns

b.

Summary, Procedure, & Formula columns

c.

Summary, Placeholder, & Procedure column

d.

Procedure, Formula, & Placeholder columns

Answer

a.

Explanation

Define Placeholder Column
  • Summary, Formula & Placeholder columns are the three types of calculated columns.

Summary Column

  • Used for calculating summary information like sum, average etc. on particular columns of a data group.
  • Use a set of oracle aggregate functions.
  • Datatypes of summary column depend on the data type of the source of the summary.

    Following Standard Functions Are Provided by a Summary Column

    • Average
    • Count
    • First
    • Last
    • Maximum
    • Minimum
    • % of Total
    • Sum
    • Variance

Formula Column

  • Allows user-defined computation on the data from of one or more columns.
  • Used to apply some custom logic on input data and return some value.
  • Written using PL/SQL syntax and use PL/SQL function for computation on the data.
  • Value can be character, number, or data and returned value match data type.

Place Holder Column

  • An empty container at design time.
  • Used to hold some value at runtime.
  • Like local or global variables- used in the logic of a formula column or in report triggers.
  • Value can be directly accessible in the report layout.

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