In today’s data-driven world, proficiency in SQL (Structured Query Language) is essential for any aspiring data professional. Oracle SQL, in particular, is widely used in enterprise environments for managing and manipulating relational databases. If you’re preparing for an interview that involves Oracle SQL, it’s crucial to familiarize yourself with common queries and concepts that are often tested. This blog will cover various Oracle SQL <\/a>queries and concepts that you should master to excel in your Oracle SQL Queries for Interview.<\/p>\n\n\n\n The most fundamental operation in SQL is the This query retrieves all columns from the The This query retrieves the first and last names of employees who work in department 10.<\/p>\n\n\n\n To sort the result set, you use the This query retrieves the first and last names of employees sorted by their last name in ascending order.<\/p>\n\n\n\n Aggregation functions, such as This query counts the number of employees in department 10.<\/p>\n\n\n\n Joins are used to combine rows from two or more tables based on a related column between them.<\/p>\n\n\n\n This query retrieves the first name, last name, and department name of employees by joining the This query retrieves all employees’ names and their respective departments, including employees who are not assigned to any department.<\/p>\n\n\n\n The This query retrieves the number of employees in each department.<\/p>\n\n\n\n Subqueries are nested queries used within another SQL query to perform additional operations.<\/p>\n\n\n\n This query retrieves the first and last names of employees whose salary is above the average salary.<\/p>\n\n\n\nBasic SQL Queries<\/h2>\n\n\n\n
Selecting Data<\/h3>\n\n\n\n
SELECT<\/code> statement, used to retrieve data from a database.<\/p>\n\n\n\nSELECT * FROM employees;
<\/code><\/pre>\n\n\n\nemployees<\/code> table. However, it’s often more efficient to specify only the columns you need:<\/p>\n\n\n\nSELECT employee_id, first_name, last_name FROM employees;
<\/code><\/pre>\n\n\n\nFiltering Data<\/h3>\n\n\n\n
WHERE<\/code> clause is used to filter records based on specified conditions.<\/p>\n\n\n\nSELECT first_name, last_name FROM employees WHERE department_id = 10;
<\/code><\/pre>\n\n\n\nSorting Data<\/h3>\n\n\n\n
ORDER BY<\/code> clause.<\/p>\n\n\n\nSELECT first_name, last_name FROM employees ORDER BY last_name ASC;
<\/code><\/pre>\n\n\n\nAggregating Data<\/h3>\n\n\n\n
COUNT<\/code>, SUM<\/code>, AVG<\/code>, MAX<\/code>, and MIN<\/code>, are used to perform calculations on a set of values.<\/p>\n\n\n\nSELECT COUNT(*) FROM employees WHERE department_id = 10;
<\/code><\/pre>\n\n\n\nIntermediate SQL Queries<\/a><\/h2>\n\n\n\n
Joining Tables<\/h3>\n\n\n\n
Inner Join<\/h4>\n\n\n\n
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SELECT e.first_name, e.last_name, d.department_name\nFROM employees e\nINNER JOIN departments d ON e.department_id = d.department_id;\n<\/code><\/pre>\n\n\n\nemployees<\/code> and departments<\/code> tables.<\/p>\n\n\n\nLeft Join<\/h4>\n\n\n\n
SELECT e.first_name, e.last_name, d.department_name
FROM employees e
LEFT JOIN departments d ON e.department_id = d.department_id;
<\/code><\/pre>\n\n\n\nGrouping Data<\/h3>\n\n\n\n
GROUP BY<\/code> clause groups rows that have the same values in specified columns into summary rows.<\/p>\n\n\n\nSELECT department_id, COUNT(*) AS employee_count
FROM employees
GROUP BY department_id;
<\/code><\/pre>\n\n\n\nSubqueries<\/h3>\n\n\n\n
SELECT first_name, last_name
FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);
<\/code><\/pre>\n\n\n\n