What SQL Construct Enables The Definition Of A Relation? What Constructs Allow Modification Of Relation Instance? (OR) Explain How Insertion, Deletion And Updating Of Database Are Performed In Relation Algebra?

In SQL, the CREATE TABLE statement is used to define a relation, which creates a new table in the database with the specified columns and data types.

To modify a relation instance (i.e., the data in a table), SQL provides several constructs:

• INSERT INTO: used to add new rows to a table
• DELETE FROM: used to remove one or more rows from a table
• UPDATE: used to modify the values in one or more rows of a table

For example, to insert a new row into a table called students with columns name, age, and major, you could use the following SQL statement:

sql
INSERT INTO students (name, age, major) VALUES ('John Doe', 22, 'Computer Science');

To delete all rows from the students table where the major column is 'Biology', you could use the following SQL statement:

sql
DELETE FROM students WHERE major = 'Biology';

To update the age column for all rows in the students table where the major column is 'Computer Science', you could use the following SQL statement:

sql
UPDATE students SET age = age + 1 WHERE major = 'Computer Science';

In relational algebra, insertion, deletion, and updating of a database are performed using the following operators:

• INSERT: adds a new tuple to a relation
• DELETE: removes a tuple from a relation
• UPDATE: modifies the value of one or more attributes in a tuple

For example, to insert a new tuple into a relation Students with attributes Name, Age, and Major, you could use the following relational algebra expression:

r
Students <- Students U {(John Doe, 22, Computer Science)}

To delete all tuples from the Students relation where the Major attribute is 'Biology', you could use the following relational algebra expression:

scss
Students <- Students - (σ(Major='Biology')(Students))

To update the Age attribute for all tuples in the Students relation where the Major attribute is 'Computer Science', you could use the following relational algebra expression:

go
Students <- Students {Age:=Age+1 | Major='Computer Science'}

In both SQL and relational algebra, these constructs allow you to manipulate the data in a relation instance, enabling you to add, remove, and modify the data as needed.