ORACLE SQL Query Order of Operations (Basic 1 - 7)

ORACLE SQL query order of operations is the sequence in which ORACLE processes the different clauses of a SQL query. The order of operations is as follows:

1. FROM
2. JOINs
3. GROUP BY
4. HAVING
5. WHERE
6. SELECT
7. ORDER BY

ORACLE will process the clauses in order, from top to bottom. This means that the FROM clause is processed first, followed by the JOINs clause, and so on.

Understanding the ORACLE SQL Query Logical Processing Order

Here is a more detailed explanation of the ORACLE SQL query logical processing order:

• FROM clause: The FROM clause specifies the tables from which the data will be retrieved. ORACLE will first identify the tables that need to be accessed, and then it will join the tables together, if necessary.
• JOINs clause: The JOINs clause specifies how to join the tables together. ORACLE will join the tables together based on the join conditions that are specified in the JOINs clause.
• GROUP BY clause: The GROUP BY clause groups the data together based on the specified columns. ORACLE will first group the data together, and then it will apply the HAVING clause to the groups.
• HAVING clause: The HAVING clause filters the groups of data based on the specified conditions. ORACLE will apply the HAVING clause to the groups of data, and then it will return the groups that meet the conditions.
• WHERE clause: The WHERE clause filters the data based on the specified conditions. ORACLE will apply the WHERE clause to the data, and then it will return the rows that meet the conditions.
• SELECT clause: The SELECT clause specifies the columns that will be returned in the result set. ORACLE will project the data based on the columns that are specified in the SELECT clause.
• ORDER BY clause: The ORDER BY clause sorts the data in the result set based on the specified columns. ORACLE will sort the data in the result set, and then it will return the sorted data to the user.

Examples

Here are some examples of SQL queries that illustrate the ORACLE SQL query order of operations:

SQL

-- Simple SELECT query
SELECT *
FROM employees;

-- SELECT query with a JOIN clause
SELECT employees.last_name, departments.department_name
FROM employees
JOIN departments ON employees.department_id = departments.department_id;

-- SELECT query with a GROUP BY clause
SELECT department_id, COUNT(*) AS num_employees
FROM employees
GROUP BY department_id;

-- SELECT query with a HAVING clause
SELECT department_id, COUNT(*) AS num_employees
FROM employees
GROUP BY department_id
HAVING COUNT(*) > 10;

-- SELECT query with a WHERE clause
SELECT last_name, salary
FROM employees
WHERE salary > 100000;

-- SELECT query with an ORDER BY clause
SELECT last_name, salary
FROM employees
ORDER BY salary DESC;

Conclusion

Understanding the ORACLE SQL query order of operations is important for writing efficient and effective SQL queries. By understanding the order in which the clauses are processed, you can write queries that will be executed quickly and accurately.