Maximizing Performance: Tips for Optimizing Your Oracle SQL Statements（oracle语句优化器）

Optimizing Oracle SQL Statements is an important step in boosting the performance of your Oracle databases. The goal of optimizing SQL statements is to make the most efficient use of the computational power available in the database to enable the best possible performance.

There are several steps to optimizing Oracle SQL Statements, including using proper aliases, indexing columns, using small table scans, using cost-based optimization, and caching results.

To start, proper aliases should be used. Aliases can be used to give tables or columns an easy to remember name while still being easy to reference within the query. For example, instead of writing the following query:

SELECT id, first_name, last_name, phone 
FROM contacts 

you could use an alias to shorten the query:

SELECT c.id, c.first_name, c.last_name, c.phone
FROM contacts c
``` 
Using aliases can significantly speed up a query because the database can easily reference the alias.

Next, indexing can be used to improve query performance. Indexing helps in cases where the query needs to look up data in tables whenever it needs to be retrieved, as the index is maintained in order so that it can quickly provide the column data needed to return a result. Indexes can also provide better cardinality, allowing optimizer to provide query cost estimates more accurately.

Small table scans should also be used when possible. The smaller the amount of data Oracle SQL has to parse, the better the query will perform. The smaller the table scan, the fewer rows Oracle SQL will need to process and the faster it will produce the query results.

Caching can also be used to improve performance. When caching a query, query result sets are stored in memory so that Oracle SQL can more quickly retrieve them and produce results. This technique can drastically speed up the query performance due to the reduced amount of work Oracle SQL will need to do to retrieve the query results.

Cost-based optimization should also be used when optimizing Oracle SQL queries. Cost-based optimization is an approach that looks at the resources each step of the process requires, and can determine the cheapest and most efficient way to attain the results desired. This can help reduce the amount of computational resources necessary to perform an operation to improve the overall query performance.

Optimizing Oracle SQL statements is an important step in improving query performance. By using proper aliases, indexing columns, using small table scans, cost-based optimization, and caching results, you can dramatically improve the speed and efficiency of your Oracle SQL queries.