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Interview Questions and Answers on .Net Framework, OOPS, ASP.Net, C#.Net, SQL Server, WCF Series – Part 29

 

Question 281 – How to Select an Authentication Mode in SQL Server?

  • Microsoft’s best practice recommendation is that you use Windows authentication mode whenever possible.
  • The main benefit is that the use of this mode allows you to centralize account administration for your entire enterprise in a single place: Active Directory.
  • This dramatically reduces the chances of error or oversight.


Question 282 – What is an Identity?

  • Identity (or AutoNumber) is a column that automatically generates numeric values.
  • A start and increment value can be set, but most DBA leave these at 1.
  • A GUID column also generates numbers; the value of this cannot be controlled.
  • Identity/GUID columns do not need to be indexed.
  • SELECT @@IDENTITY - returns the last IDENTITY value produced on a connection
  • SELECT IDENT_CURRENT('tablename') - returns the last IDENTITY value produced in a table
  • SELECT SCOPE_IDENTITY() - returns the last IDENTITY value produced on a connection


Question 283 – What are INNER JOINs in SQL?

  • This join returns rows when there is at least one match in both the tables.
  • Select * From Table1 Inner Join Table2 ON table1.ColumnName = Table2.ColumnName


Question 284 – What is a LEFT OUTER JOIN in SQL?

  • This join returns all the rows from the left table in conjunction with the matching rows from the right table.
  • If there are no columns matching in the right table, it returns NULL values.
  • Example - Select * From Table1 LEFT Join Table2 ON table1.ColumnName = Table2.ColumnName


Question 285 – What is a RIGHT OUTER JOIN in SQL?

  • This join returns all the rows from the right table in conjunction with the matching rows from the left table.
  • If there are no columns matching in the left table, it returns NULL values.
  • Example - Select * From Table1 RIGHT Join Table2 ON table1.ColumnName = Table2.ColumnName

 

Question 286 – What is a FULL OUTER JOIN in SQL?

  • This join combines left outer join and right after join. It returns row from either table when the conditions are met and returns null value when there is no match.
  • Example - Select * From Table1 FULL Join Table2 ON table1.ColumnName = Table2.ColumnName


Question 287 – What is an EQUI JOIN in SQL?

It is a specific type of comparator-based join, or the join that uses only equality(only =) comparisons in the join-predicate.


Question 288 – What is a CROSS JOIN in SQL?

  • It produces the Cartesian product of the tables involved in the join.
  • A cross join that does not have a WHERE clause
  • The size of a result set is the no of rows in the 1st table multiplied by the no of rows in the 2nd table.
  • Example: is when company wants to combine each product with a pricing table to analyze each product at each price.


Question 289 – What is a SELF JOIN in SQL?

Same table is specified twice with two different aliases in order to match the data within the same table.


Question 290 – What is a NATURAL JOIN in SQL?

  • It offers a further specialization of equi-joins.
  • The join predicate arises implicitly by comparing all columns in both tables that have the same column-name in the joined tables.
  • The resulting joined table contains only one column for each pair of equally-named columns.
  • Example - SELECT * FROM Vendor NATURAL JOIN advance

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About Author: Karthikeyan Anbarasan, Microsoft MVP (Most Valuable Professional) in ASP.NET/IIS Architecture. He is the Founder and Chief Editor of the www.f5debug.net website and has authored books on Windows Phone and Business Intelligence(SSIS). He is also a Passionate Speaker and a Blogger on Microsoft Technologies.

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