How to use with in oracle

WITH clause creates temporary tables or views in Oracle, used to create complex temporary tables or views, rename query results and improve query performance: Create temporary tables: WITH clause_name AS (subquery) Rename query Result: WITH clause_name AS (subquery) Improve query performance: Store subqueries in temporary tables to improve performance

WITH clause in Oracle Usage

What is WITH clause?

WITH clause is used in Oracle to create temporary tables or views that are visible only in the current session.

Syntax

<code>WITH clause_name AS (subquery)
SELECT ...
FROM ...</code>

• clause_name: The name of the temporary table or view.
• subquery: Query statement, used to create temporary tables or views.

Usage

WITH clause is usually used in the following scenarios:

• Create complex temporary tables or views for Inquiry.
• Rename the results of complex queries to simpler names for easy subsequent reference.
• Improve query performance by storing the results of subqueries in temporary tables.

Example

Create temporary table

<code>WITH EmployeeTemp AS (
  SELECT employee_id, salary, department_id
  FROM Employees
  WHERE salary > 10000
)
SELECT * FROM EmployeeTemp;</code>

Rename query results

<code>WITH EmployeeSalaries AS (
  SELECT employee_id, salary
  FROM Employees
)
SELECT employee_id, salary AS emp_salary
FROM EmployeeSalaries;</code>

Improve query performance

<code>WITH EmployeeAvgSalary AS (
  SELECT department_id, AVG(salary) AS avg_salary
  FROM Employees
  GROUP BY department_id
)
SELECT * FROM EmployeeAvgSalary
WHERE avg_salary > 50000;</code>

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