oracle query parameters

Oracle is a widely used database management system that plays an important role in enterprise-level applications. In the process of using Oracle, query is a very important operation. Properly setting query parameters can improve query efficiency and reduce query time. Below, we will discuss in detail how to set Oracle query parameters.

1. Paging query parameter settings

Paging query is a very common query operation. You can limit the number of query results per page by setting parameters and control the starting position of the query.

SQL example:

SELECT * 
FROM table_name 
WHERE condition 
ORDER BY column_name 
OFFSET start_row 
FETCH NEXT row_count ROWS ONLY;

Among them, start_row represents the starting row number of the query, and row_count represents the number of rows queried on each page.

2. Optimizer parameter settings

Optimizer parameters refer to some parameter settings of the Oracle query optimizer. Oracle will dynamically adjust the query execution plan based on the conditions in the query statement and the data volume of the table when the query is executed. By setting the optimizer parameters, you can adjust the performance of the optimizer and improve query efficiency.

SQL example:

ALTER SESSION SET OPTIMIZER_MODE = ALL_ROWS;

This SQL statement can set the query optimizer mode. ALL_ROWS means that the optimizer will select the smallest full set scan to obtain the optimal query effect.

3. Parallel query parameter setting

Parallel query refers to a way for Oracle database to execute queries simultaneously among multiple CPUs. It can be set by setting the parallelism of the query. Improve query speed.

SQL example:

SELECT /*+ PARALLEL(table_name, degree) */ *
FROM table_name
WHERE condition;

Among them, degree represents the degree of parallelism and can be set to a number, indicating how many CPUs the query will use to execute. This parameter is only meaningful for large queries and large tables.

4. SQL Cache Parameter Settings

Oracle database can maintain a cache of SQL statements to speed up query response. You can control cache usage by setting SQL cache parameters.

SQL example:

ALTER SYSTEM SET cursor_sharing = FORCE;

This SQL statement can set the sharing mode of the SQL cache. FORCE means that the database will use similar SQL statements to share the cache to reduce query time.

5. Precompilation parameter settings

Oracle supports precompiling SQL statements to improve query performance. You can control the use of precompilation by setting precompilation parameters.

SQL example:

EXECUTE DBMS_PREPROCESSOR.PREREMOVE('SELECT * FROM table_name WHERE condition');

This SQL statement can set the parameters of the preprocessor to control the preprocessed SQL statement.

In short, in Oracle queries, setting query parameters reasonably is an important part of improving query efficiency. The query parameters discussed above can help users better master Oracle query skills, improve query efficiency, and also enhance the performance of the Oracle database. Due to the complexity and diversity of Oracle queries, in order to better optimize query performance, it is recommended that novice users improve their skills by reading official documents or referring to classic books.

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