Q.Which of the following SQL command can change the degree of the existing relation ? (A) DROP TABLE (B) ALTER TABLE (C) UPDATE…SET (D) DELETE

The key idea is that the degree of a relation is the number of attributes (columns) it has. To change the degree, you must add or remove a column.

• DROP TABLE removes the entire relation — not just a column.
• UPDATE…SET modifies existing data values, not the schema.
• DELETE removes rows (tuples), not columns. …

The concept: degree of a relation

In relational database terminology, the degree of a relation (table) is simply the number of attributes (columns) it contains. For example, a Student table with columns RollNo, Name, Age has degree 3.

If you want to change the degree, you must either add a new column (increasing the degree) or remove an existing column (decreasing the degree). This is a structural change to the table schema — not a change to the data inside the table.

Why each option does or doesn't change the degree

Let's examine each SQL command:

1. DROP TABLE — This removes the entire table from the database. It doesn't change the degree of an existing relation; it destroys the relation itself. So this is not about altering degree.

2. ALTER TABLE — This command is specifically designed to modify the structure of an existing table. You can use it with clauses like:

   • ADD column_name datatype — adds a new column, increasing the degree.
   • DROP COLUMN column_name — removes an existing column, decreasing the degree.

   Therefore, ALTER TABLE can directly change the degree of a relation.

3. UPDATE…SET — This modifies the values of existing rows in a table. It changes the content of cells, but it never adds or removes columns. The degree remains exactly the same.

4. DELETE — This removes rows (tuples) from a table. It changes the cardinality (number of rows), but not the degree. The column structure is untouched. …