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Hi, given Sql server executes queries order from, where, group by, having, select, order by. Why don't we write queries in same order? Would that improve speed of execution ?
I guess that is why you do not use many indexes in OLTP setup? I mean, since they do mostly inserts, updates and deletes.jedishrfu said:No the sql engine constructs an execution tree and decides how to best execute the query.
Some systems have a describe or explain command that will show how the query will be executed and the actual tables it will use.
It can be quite surprising too. As an example you might have built an index table to speed your query only to discover that it’s not being used. This may mean a different index table is needed.
One caveat is it can be a negative to create too many index tables especially in a high performance application where data is added and deleted constantly. Each time you add or drop data the associated index tables needed to be added to or deleted from.
It seems from doing informal research that SQL Server will not execute queries that are not done in the order : SELECT FROM WHERE GROUP BY HAVING ORDER BY. I get error messages every time I try any query that violates this order sequence.jedishrfu said:No the sql engine constructs an execution tree and decides how to best execute the query.
Some systems have a describe or explain command that will show how the query will be executed and the actual tables it will use.
It can be quite surprising too. As an example you might have built an index table to speed your query only to discover that it’s not being used. This may mean a different index table is needed.
One caveat is it can be a negative to create too many index tables especially in a high performance application where data is added and deleted constantly. Each time you add or drop data the associated index tables needed to be added to or deleted from.
The order of execution refers to the sequence in which SQL statements are processed by the database engine. This is determined by the logical processing order, which can be affected by factors such as the use of subqueries or the presence of nested views. On the other hand, design in SQL Server refers to the structure and organization of the database, including tables, columns, indexes, and relationships.
The order of execution can impact the performance and efficiency of a database design. For example, if a query is frequently executed and involves multiple subqueries, it may be beneficial to redesign the database by creating views or indexes to improve the logical processing order and reduce execution time.
The logical processing order in SQL Server is determined by the database engine and cannot be directly changed. However, database designers and developers can optimize their database design to influence the order of execution and improve performance.
The order of execution can impact the result of a query in SQL Server, particularly when the query involves complex logic or joins. If the logical processing order is not optimized, the result may be incorrect or take longer to retrieve.
Yes, the design of a database in SQL Server can impact the order of execution. For example, if a table is heavily indexed, it may improve the logical processing order and result in faster execution of queries. Similarly, a poorly designed database with redundant or unnecessary tables can lead to a less efficient order of execution.