A foreign key constraint enforces referential integrity by linking a column in one table to the primary key of another table. Explanation: Example SQL Foreign Key Constraint: sqlCopyEditCREATE TABLE Employees ( emp_id INT PRIMARY KEY, dept_id INT, FOREIGN KEY (dept_id) REFERENCES Departments(dept_id) ON DELETE SET NULL ); Here, if a department is deleted, dept_id in…

Data redundancy occurs when the same piece of data is stored multiple times in a database. Explanation:

Referential integrity ensures that relationships between tables remain consistent by enforcing foreign key constraints. Explanation: Example SQL Enforcing Referential Integrity: sqlCopyEditCREATE TABLE Orders ( order_id INT PRIMARY KEY, customer_id INT, FOREIGN KEY (customer_id) REFERENCES Customers(customer_id) ON DELETE CASCADE ); Here, if a customer is deleted, all their orders are automatically deleted (ON DELETE CASCADE).

A composite key is a primary key that consists of two or more attributes that uniquely identify a record. Explanation: Example SQL Composite Key: sqlCopyEditCREATE TABLE Enrollment ( student_id INT, course_id INT, enrollment_date DATE, PRIMARY KEY (student_id, course_id) ); Here, student_id and course_id together form a composite key.

A candidate key is an attribute (or set of attributes) that can uniquely identify each tuple in a table. Explanation: Example: For a Students table: student_id email name 101 alice@email.com Alice Here, student_id and email are candidate keys, as both uniquely identify a student.

A tuple is a single record (row) in a relational database table. Explanation: Example: For the Employees table: emp_id name dept_id 1 Alice 10 The row (1, Alice, 10) is a tuple.

A schema is the logical structure of a database, defining tables, columns, relationships, constraints, and indexes. Explanation: Example Schema Definition in SQL: sqlCopyEditCREATE SCHEMA School; CREATE TABLE School.Students ( student_id INT PRIMARY KEY, name VARCHAR(50), age INT ); Here, we created a schema named School and a table Students within it.

A subquery (also known as a nested query) is an SQL query that is embedded inside another SQL query. Explanation: Example: Find employees who earn more than the average salary in the company. sqlCopyEditSELECT name, salary FROM Employees WHERE salary > (SELECT AVG(salary) FROM Employees); Here, the subquery (SELECT AVG(salary) FROM Employees) calculates the average…

An OUTER JOIN retrieves all records from one or both tables, even if there are no matches, by filling missing values with NULLs. Explanation: There are three types of outer joins: Example: SQL Query for LEFT OUTER JOIN: sqlCopyEditSELECT Employees.name, Departments.department_name FROM Employees LEFT OUTER JOIN Departments ON Employees.dept_id = Departments.dept_id; Output: name department_name Alice…

An INNER JOIN in SQL returns only the rows where there is a match in both tables based on a specified condition. Explanation: Example: Consider two tables:Employees Table emp_id name dept_id 1 Alice 10 2 Bob 20 3 Charlie 30 Departments Table dept_id department_name 10 HR 20 IT SQL Query for INNER JOIN: sqlCopyEditSELECT Employees.name,…