SQL Query Structure

There are two types of Execution plan in SQL Server i.e. Estimated execution plan Actual execution plan Estimated execution plan is generated based on the statistics available for the SQL table columns and indexes. The estimated execution plan may differ from the actual execution plan as the latter is generated when the query is executed and depicts the execution mechanism followed by the server in order to generate the query in the best possible way (least time). Execution plan is the steps taken by the SQL server optimiser to reach the SQL query results in best possible way. We always have questions such as why our query is running slow, how we can reduce the time to execute the query. The query which is to be executed is submitted to the SQL Server, the query optimiser is responsible for parsing the query and generating the execution plan. When the query is submitted to the system, there are many underlying operation that are happening in the backend before the result is...

The following steps show the logical processing order, or binding order, for a SELECT statement. This order determines when the objects defined in one step are made available to the clauses in subsequent steps. For example, if the query processor can bind to (access) the tables or views defined in the FROM clause, these objects and their columns are made available to all subsequent steps. Conversely, because the SELECT clause is step 8, any column aliases or derived columns defined in that clause cannot be referenced by preceding clauses. However, they can be referenced by subsequent clauses such as the ORDER BY clause.  Note that the actual physical execution of the statement is determined by the query processor and the order may vary from this list. which gives the following order: FROM ON JOIN WHERE GROUP BY WITH CUBE or WITH ROLLUP HAVING SELECT DISTINCT ORDER BY TOP Complete SELECT query SELECT DISTINCT column, AGG_FUNC( column_or_expression ), … F...