How to query the database in oracle

After connecting to the database through SQL*Plus or other clients, use the SELECT statement to query, which includes: the retrieval column, the table to be queried, and the optional WHERE clause for filtering. After executing the query, the results will be displayed in tabular form.

How to use Oracle to query the database

Oracle provides powerful query capabilities that allow database users to retrieve specific information. Here is a step-by-step guide to querying a database using Oracle:

1. Establish a connection

• Connect to the database using SQL*Plus or other Oracle client tools.
• Enter the following command:

<code>connect username/password@database_name</code>

2. Write the query statement

• The query statement consists of SELECT Begins with a keyword, followed by the column to be retrieved, or * (for all columns).
• Next is the FROM keyword, followed by the name of the table to be queried.
• The optional WHERE clause is used to filter the results.

Sample query:

<code>SELECT * FROM employees WHERE last_name = 'Jones';</code>

3. Execute the query

• In SQL*Plus, Press F5 or enter the following command:

<code>;</code>

4. View the results

• The query results will be displayed in the command line.
• The results will be displayed in a table, with each row representing a record.

Advanced query functions:

• Aggregation functions: Used to group and summarize data, such as SUM(), COUNT() and AVG().
• JOIN: is used to combine data from multiple tables .
• Subquery: Embedded query in the main query.
• Sort: Use the ORDER BY clause to sort the results based on columns.

Tips:

• Use the DESCRIBE table_name command to view the column information of the table.
• Learn SQL syntax to take full advantage of Oracle's query capabilities.
• Simplifly query process using tools (such as SQL Developer).

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