Databases hold a crucial role in the performance of online operations which makes them quite essential to keep them optimized for an overall higher performance. For a database to operate seamlessly, it should be performance-tuned and optimized on a frequent basis. Oracle is one of the most popular databases used by users for optimizing the speed. In the Oracle database, query optimization plays a significant role in tuning the performance of the database.

There are several ways in which an SQL query can be optimized and that’s what we are here to read about. But before leaping on to the Oracle SQL query optimization techniques, let us first understand the term query optimization completely.

What is Oracle Query Optimization?

In simple words, query optimization can be defined as the process of selecting the most effective means of executing a SQL statement. By nature, SQL is non-procedural which means that the optimizer is free to reorganize, process, and merge the SQL statements in any order for the utmost efficiency.

Depending on the statistics gathered on the accessed data, every SQL statement is optimized by the database. The optimizers identify the optimal plan for a SQL statement. This is done by analyzing multiple access methods including index scans or full table scans, different join methods like hash joins and nested loops, possible transformations, and different join orders.

Experimented Oracle SQL Query Optimization Techniques

Here we have described some of the used oracle SQL query optimization techniques that are surely going to performance tune your database if used properly:

• Begin with the System Level SQL tuning

To begin with the SQL query optimization, firstly, it’s essential to perform SQL tuning at the system level or other changes automatically get undo. It leads to rework in performance tuning.

• Along with temporary tables, rewrite complex sub queries

With SQL WITH operator and GTT (Global Temporary Table), rewriting complex sub queries in Oracle SQL is pretty easy and simple. This is beneficial in complex sub queries such as FROM clause in-line views, SELECT clause scalar sub queries, and WHERE clause sub queries. After tuning with the temporary tables with queries and WITH clause, the performance of the SQL query in Oracle may improve by many folds in certain environment such as same sub queries appears multiple times in a SQL statement.  This method is not applicable when the sub queries can be effectively merged into main query by Oracle SQL optimizer.

• Instead of Outer Joins, make use of inner joins

Outer joins should be used only when it is required, in the rest of the cases, try replacing them with inner joins for a better performing SQL query. Since outer joins slow down the SQL execution, thereby, affecting optimization, hence, using inner joins is highly recommendable for better performance.

• Index all the predicates

Indexing all the predicates of WHERE, JOIN, GROUP BY and ORDER By clauses in SQL queries increases the performance as well as scalability of the database and query. In the absence of the proper indexing, it lets table scanning of SQL queries which consequently results in locking issues or performance. Hence, it is intelligent to index all the predicates except where the column data has low cardinality.

• Use BLOB/CLOB columns

Oracle 10g and 11g need BLOB/CLOB columns; otherwise, it will lead to an execution failure when the input value size is beyond 1000 characters.