Tuesday, June 29, 2010

What are the advantages of stored procedures, triggers, indexes?

Stored procedure : Stored procedureis a set of SQL commands that can be compiled and stored in the server. Once this process has been done, user don’t need to keep re-issuing the entire query he can refer to the stored procedure. This provides better overall performance because the query has to be parsed only once and less information needs to be sent between the server and the user. We can also raise the conceptual level by having libraries of functions in the server. However, stored procedures of course do increase the load on the database server system, as more of the work is done on the server side and less on the client (application) side.

Trigger : A trigger is effectively a type of stored procedure, one that is invoked when a particular event occurs. For example, we can install a stored procedure that is triggered each time a record is deleted from a transaction table and that stored procedure automatically deletes the corresponding customer from a customer table when all his transactions are deleted.

Indexes : Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly determine the position to seek to in the middle of the data file without having to look at all the data. If a table has 1,000 rows, this is at least 100 times faster than reading sequentially. If you need to access most of the rows, it is faster to read sequentially, because this minimizes disk seeks.

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