oracle query efficiency

Oracle query is an important operation of the database and one of the most commonly used methods when operating the database. Good query efficiency can effectively improve the data processing speed and response time of the database, and greatly enhance the performance of the database. Therefore, mastering Oracle query methods and techniques is of great significance for improving the efficiency and performance of the database.

In order to improve the efficiency of Oracle queries, we need to start from the following aspects.

1. Create an index

An index is a data structure used to speed up data retrieval. Creating an index is to create an index for one or more columns in a database table. When you query this table, you can quickly locate the required row data through this index. When performing query operations, indexes should be used to speed up queries. When using indexes, pay attention to creating indexes for the most commonly used columns, and do not need to index some rarely used columns.

2. Use views correctly

A view is a virtual table generated using SQL statements based on the data stored in the table. It has the same data format as the actual table. Views can simplify query statements and improve query efficiency. If some queries are used frequently, and these queries often include JOIN of multiple tables, you can use the view to preprocess all the JOIN operations of these tables so that the view can be called directly later.

3. Use the optimizer

Oracle optimizer is a query processing engine. You can use this tool to optimize query planning, calculate different query plans, and obtain the best query plan. When using Oracle queries, you should be good at using the optimizer and use different optimizer query methods for different situations.

4. Avoid using SELECT *

"SELECT " will query all columns in the table. For large tables, it will cause the execution speed of SQL statements to become very slow. In practice, not all columns need to be used every time. Therefore, when performing query operations, you should use the method of specifying column names to perform query operations and avoid using SELECT .

5. Try to use efficient query methods such as inner joins and set joins.

Use efficient query methods such as inner joins and set joins, such as using the WHERE keyword and INNER JOIN to connect tables. Effectively improve query efficiency, while using complex connection methods such as outer joins can easily lead to reduced query efficiency.

6. Avoid using fuzzy queries in queries

When using fuzzy queries, please note that "%" cannot be used on the left side of the matching conditions, which will cause the query optimizer to be unable to use index optimization. Inquire. If there are fuzzy query conditions in the column, it can be implemented using function-based indexes or full-text indexes.

7. Reduce the scope of the query

When performing query operations, try to reduce the scope of the query and avoid querying the entire table. You can avoid full table scan operations through paging queries, partition queries, etc., thereby improving query efficiency.

8. Clean up junk data in a timely manner

Junk data refers to some unused, expired or duplicate data. Once this data is stored in the database, it will occupy a certain amount of storage space, thereby reducing the performance of the entire database. Therefore, when using Oracle queries, pay attention to cleaning up junk data in time to ensure the overall performance of the database.

In short, the efficiency of Oracle query needs to be considered and improved from many aspects to achieve the best query effect. Only by fully understanding the basic knowledge and application methods of the database can we operate it freely in practical applications and continuously improve the efficiency of Oracle queries, thereby fully utilizing the performance of the database.

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