Correlated subqueries

Correlated subqueries in SQL are nested queries where the inner query references a column from the outer query. These subqueries are evaluated for each row processed by the outer query.

Consider a table named Employees with columns EmployeeID, EmployeeName, and Salary. We want to retrieve all employees whose salary is greater than the average salary of their department.

SELECT EmployeeID, EmployeeName, Salary FROM Employees e1 WHERE Salary > ( SELECT AVG(Salary) FROM Employees e2 WHERE e1.DepartmentID = e2.DepartmentID );

In this example, the subquery (SELECT AVG(Salary) FROM Employees e2 WHERE e1.DepartmentID = e2.DepartmentID) is correlated because it references the DepartmentID column from the outer query (e1). For each row processed by the outer query, the subquery calculates the average salary of the corresponding department. The outer query then retrieves the EmployeeID, EmployeeName, and Salary where the salary is greater than the average salary of the department. This query returns employees whose salary exceeds the average salary of their department.

Comments

TechUplift: Elevating Your Expertise in Every Click

Unlock the potential of data with SQL Fundamental: Master querying, managing, and manipulating databases effortlessly. Empower your database mastery with PL/SQL: Unleash the full potential of Oracle databases through advanced programming and optimization. Unlock the Potential of Programming for Innovation and Efficiency. Transform raw data into actionable insights effortlessly. Empower Your Data Strategy with Power Dataware: Unleash the Potential of Data for Strategic Insights and Decision Making.

SQL Fundamentals

SQL, or Structured Query Language, is the go-to language for managing relational databases. It allows users to interact with databases to retrieve, manipulate, and control data efficiently. SQL provides a standardized way to define database structures, perform data operations, and ensure data integrity. From querying data to managing access and transactions, SQL is a fundamental tool for anyone working with databases. 1. Basics of SQL Introduction : SQL (Structured Query Language) is used for managing and manipulating relational databases. SQL Syntax : Basic structure of SQL statements (e.g., SELECT, INSERT, UPDATE, DELETE). Data Types : Different types of data that can be stored (e.g., INTEGER, VARCHAR, DATE). 2. SQL Commands DDL (Data Definition Language) : CREATE TABLE : Define new tables. ALTER TABLE : Modify existing tables. DROP TABLE : Delete tables. DML (Data Manipulation Language) : INSERT : Add new records. UPDATE : Modify existing records. DELETE : Remove records. DQL (Da...

DAX Functions

These are just some of the many DAX functions available in Power BI. Each function serves a specific purpose and can be used to perform a wide range of calculations and transformations on your data. Aggregation Functions: SUM : Calculates the sum of values. AVERAGE : Calculates the arithmetic mean of values. MIN : Returns the smallest value in a column. MAX : Returns the largest value in a column. COUNT : Counts the number of rows in a table or column. COUNTA : Counts the number of non-blank values in a column. DISTINCTCOUNT : Counts the number of unique values in a column. Logical Functions: IF : Returns one value if a condition is true and another value if it's false. AND : Returns TRUE if all the conditions are true, otherwise FALSE. OR : Returns TRUE if any of the conditions are true, otherwise FALSE. NOT : Returns the opposite of a logical value. Text Functions: CONCATENATE : Concatenates strings together. LEFT : Returns the leftmost characters from a text string. RIGHT : Ret...

DataMindSphere

Search This Blog