SQL- COUNT Function - The Diigo Meta page

• 05 Sep 12
  

  darkpanda89
  • COUNT function returns the number of rows in a query.
  • SELECT COUNT(expression)
      FROM tables
      WHERE predicates;
  • ield in the brackets is NOT NULL.
  • use the DISTINCT clause within the COUNT function.

  2 more annotations...

• 04 Apr 12
  

  julianez

  2008-08-13 Fecha imported

• 24 Oct 11
  

  sgandhi017

  • A more efficient implementation of the same solution would be the following SQL statement:

     

     

    SELECT COUNT(1) as "Number of employees"
     FROM employees
     WHERE salary > 55000;
  • Now, the COUNT function does not need to retrieve all of the fields from the table (ie: employee_number, employee_name, and salary), but rather whenever the condition is met, it will retrieve the numeric value of 1. Thus, increasing the performance of the SQL statement.
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