Wednesday, June 9, 2021

SQL Concept- Part 3

 In this blog we are going to understand the important and basic concepts of SQL.


 1.Union :

  • Union operator selects only distinct values.
  • Union removes duplicate records.
       Example:







2.Union All: 

  • Union All keeps all records from each data sets. 
  • Union All is used to allow duplicate values.
         Example:
          






3.Oder By:

  •  The Order By clause is used for sorting data in ascending and descending order based on one or more columns.
         Example:







4.Group By:

  • Group By is used to group the rows that have the same values.
  • This clause is used with this SELECT statement.
  • The Group By clause is used with aggregate functions like: COUNT , MAX, MIN, SUM, and AVG.
        Example:





5.Subquery:

  • Subquery is also termed as nested subquery.
  • Subquery is nothing but query inside a query.
  • While the statement containing a subquery is also called an outer query or outer select.
  • In a subquery first, execute inner query and result pass to outer query then outer query executes.
         Example:







2.Correlated subqueries:

  • Correlated subquery is a subquery that uses values from the outer query.
  • The inner query needs an outer query value. Then the result pass to the outer query.
  • Correlated subquery depends upon the outer query and cannot execute on its own.
  • In this query, By using the EXISTS operator we define correlated subquery.
       Example:







For more understanding watch below video :




Thank you!!!!






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