Retrieve Data from Oracle: SQL Guide

To extract important data in Oracle database, you can use SQL query statements and relevant functions of Oracle database.

Here are some ways to extract important data in Oracle database:

1. The SELECT statement is used to query data. It allows you to retrieve data from a database table by specifying the columns and conditions to filter out the required information. For example, SELECT * FROM table_name WHERE condition;
2. Aggregate functions are used for data summarization: By using aggregate functions such as SUM, COUNT, and AVG, data can be summarized. You can use these functions to extract the total sum, count, or average values of the data. For example, SELECT SUM(column_name) FROM table_name;
3. Use JOIN operation to connect multiple tables: If you need to extract data from multiple tables, you can use JOIN operation to connect them. JOIN operation combines rows from multiple tables based on the values in common columns. For example, SELECT * FROM table1 JOIN table2 ON table1.column_name = table2.column_name;.
4. Retrieve nested query results using a subquery: Embedding a subquery within a query allows you to retrieve data based on the results of the main query. This is very useful for extracting important data from a single query. For example, SELECT * FROM table_name WHERE column_name IN (SELECT column_name FROM another_table WHERE condition);.
5. Arrange the results using ORDER BY: Utilizing the ORDER BY clause allows you to sort the results by a specified column. This is helpful for viewing important data in a specific order. For example, SELECT * FROM table_name ORDER BY column_name ASC;.
6. Grouping data using GROUP BY: Using the GROUP BY statement allows you to group results by a specified column. This is very useful for categorizing and analyzing data. For example, SELECT column_name1, SUM(column_name2) FROM table_name GROUP BY column_name1;
7. Limit the size of the result set using LIMIT (or ROWNUM): If you only need to fetch the top few rows of data, you can use the LIMIT clause (or ROWNUM in Oracle) to restrict the size of the result set. For example, SELECT * FROM table_name WHERE condition ORDER BY column_name LIMIT 10;

Please choose a suitable method based on your needs, and make corresponding adjustments according to the database structure and data. You can also refer to the official documentation and tutorials of Oracle database to learn more about methods and techniques for data extraction.