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SQL INTERVIEW QUESTIONS & ANSWERS

Databases
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36. What is unique key?
  The unique key constraint ensures that information in the column(s) is unique or value entered in unique column must not be repeated across the column(s). A table may have more than one unique key. Unique key can be null at the time of data entry. So value is not mandatory in unique column.
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37. What is foreign key?
  Foreign key constraint is used to represent relationship between two or more tables.
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38. What are the various data types of oracle?
 
  • BINARYJNTEGER
  • DEC
  • DECIMAL
  • DOUBLE PRECISION
  • FLOAT
  • INT
  • INTEGER
  • NATURAL
  • NATURALN
  • NUMBER
  • NUMERIC
  • REAL
  • SMALLINT
  • CHAR
  • CHARACTER
  • LONG
  • NCHAR
  • VARCHAR2
  • RAW
  • LONG RAW
  • ROWID
  • UROWID
  • BOOLEAN (Other)
  • DATE (Other)
  Posted by Srinivas. (Dec 12, 2013)
 

interval day to sec; interval year to month; timestamp timestamp(n) with time zone; timestamp(n)with local time zone
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39. What is the use of distinct keywords?
  The DISTINCT keyword is used to return only distinct (different) values.
  Posted by Gopal Suthar. (Oct 28, 2013)
 

Distinct keyword is used to find different records (no repetition). it does not allowed same record.
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40. What are views?
  Views are logical tables of data extracted from existing tables. A view can be thought of as a stored query or a VIRTUAL TABLE. We can use views in most places where a table can be used.
  Posted by Ibrahim. (Oct 09, 2013)
 

View is a virtual table. Every query has attached to it.
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