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Order of Execution

  • First, the product of all tables in the FROM clause is formed.
  • The WHERE clause is then evaluated to eliminate rows that do not satisfy the search_condition.
  • Next, the rows are grouped using the columns in the GROUP BY clause.
  • Then, groups that do not satisfy the search_condition in the HAVING clause are eliminated.
  • Next, the expressions in the SELECT statement target list are evaluated.
  • If the DISTINCT keyword in present in the select clause, duplicate rows are now eliminated.
  • The UNION is taken after each sub-select is evaluated.
  • Finally, the resulting rows are sorted according to the columns specified in the ORDER BY clause.
  • TOP clause is executed.