Clauses - (Oracle Clauses)

Clauses in Oracle SQL are special keywords that are used to modify the behavior of a SQL statement. They can be used to control the order of execution, filtering, grouping, and sorting of data in a query.

Syntax

The syntax for using clauses in Oracle SQL is as follows:

SELECT column1, column2, ...
FROM table_name
WHERE condition
GROUP BY column1, column2, ...
HAVING condition
ORDER BY column1, column2, ... ASC/DESC;

Here, SELECT is the keyword used to retrieve data from a table or view, FROM is used to specify the table or view to retrieve data from, WHERE is used to filter the results, GROUP BY is used to group the results based on one or more columns, HAVING is used to filter the results after they have been grouped, and ORDER BY is used to sort the results in ascending or descending order based on one or more columns.

Example

Here is an example of using clauses in Oracle SQL to retrieve and sort data from a table:

SELECT id, name, salary
FROM employees
WHERE department = 'Sales'
GROUP BY id, name
HAVING COUNT(*) > 1
ORDER BY salary DESC;

In this example, we are retrieving the id, name, and salary columns from the employees table, but only for employees who work in the 'Sales' department. We are grouping the results by id and name, and only returning results where there is more than one employee with the same id and name. Finally, we are ordering the results by salary in descending order.

Output

The output of the query will be a list of employees who work in the 'Sales' department, with duplicate id and name values removed, and sorted by salary.

Explanation

In the above example, we have used the WHERE clause to filter the results to only include employees who work in the 'Sales' department. We have used the GROUP BY clause to group the results based on the id and name columns, and the HAVING clause to filter out any groups with only one employee. Finally, we have used the ORDER BY clause to sort the results by salary in descending order.

Use

Clauses are an important aspect of Oracle SQL as they allow you to control how data is retrieved, filtered, grouped, and sorted. By using clauses effectively, you can create more complex queries that return the specific data you need.

Important Points

• Clauses in Oracle SQL are special keywords that are used to modify the behavior of a SQL statement.
• Clauses can be used to control the order of execution, filtering, grouping, and sorting of data in a query.
• The most commonly used clauses are SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY.
• Clauses can be combined to create more complex queries that return the specific data you need.

Summary

In summary, clauses in Oracle SQL are special keywords that are used to modify the behavior of a SQL statement. They can be used to control the order of execution, filtering, grouping, and sorting of data in a query. The most commonly used clauses are SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY. By using clauses effectively, you can create more complex queries that return the specific data you need.