3i Infotech Placement: Sample Questions 219 - 220 of 1245

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Question 219




A column defined as PRIMARY KEY can have NULL՚s




Understanding of Primary Key Constrain
  • Column defined as PRIMARY KEY cannot be null because primary key and unique key can both be used for uniquely identifying a row and unique key can have null value once.
  • PRIMARY KEY indicates a column or group of columns used as a unique identifier for rows in the table.
  • A unique constraint does not by itself it is provide a unique identifier because it does not exclude null value.
  • Primary key should be UNIQUE because a primary key identifies rows in a table so 2 different rows should not have the same key.
  • Use for PRIMARY KEY may be as foreign key in other table.
  • A primary key is cannot be null.

Question 220


Write in Short

Short Answer▾

What is the main functionality of prepared statement?


  • Prepare is used to send SQL queries.
  • Prepares stores the query in in system global area memory.
  • For same query sent a second time no compilation is done to improve performance.
  • Thus first time it is not precompiled but for the second time it is precompiled.
  • It is wrong assumption that prepared statement is precompiled statement.
  • Prepared statement have faster execution than other statements.

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