CBSE Class 12 Computer Science Chapter 6: Database Concepts NCERT Solutions

The RDBMS operation used to produce the RESULT is the Cartesian Product. This operation combines each row from the first table (PARTICIPANTS) with each row from the second table (EVENTS).

To find the Degree and Cardinality of the RESULT table:

• Degree: The degree is the number of columns in the RESULT table. The RESULT table has columns: No., Name, EVENTCODE, EVENTNAME. Therefore, the Degree is 4.
• Cardinality: The cardinality is the number of rows in the RESULT table. The PARTICIPANTS table has 3 rows, and the EVENTS table has 2 rows. The Cartesian Product results in (Number of rows in PARTICIPANTS) * (Number of rows in EVENTS) = 3 * 2 = 6 rows. Therefore, the Cardinality is 6.

Answer: Cartesian Product, Degree = 4, Cardinality = 6

Degree: The degree of a relation (or table) is defined as the number of attributes (columns) it contains. In simpler terms, it's the count of columns in the table.

Cardinality: The cardinality of a relation (or table) is defined as the number of tuples (rows or records) it contains. In simpler terms, it's the count of rows in the table.

For the given 'Patients' table:

• The attributes are PatNo, PatName, Dept, and DocID. There are 4 attributes. So, the Degree = 4.
• The tuples (rows) are: (1, Leena, ENT, 100), (2, Supreeth, Ortho, 200), (3, Madhu, ENT, 100), (4, Neha, ENT, 100), (5, Deepak, Ortho, 200). There are 5 tuples. So, the Cardinality = 5.

Answer: Degree = 4, Cardinality = 5

1. Can Qty be a primary key? No, we cannot have 'Qty' as the primary key in the 'Store' table. A primary key must uniquely identify each record in a table, meaning each value in the primary key column must be distinct. In the given 'Store' table, the 'Qty' column has values 1500 (for Item Code 11) and 1600 (for Item Code 12 and 13), which are duplicated. Since primary keys cannot have duplicate values, 'Qty' is not a suitable primary key. 'Item Code' would be a more appropriate primary key as it appears to be unique for each item.
2. Cardinality and Degree:
   • Degree: The degree is the number of columns in the table. The table has columns: Item Code, Item, Qty, Rate. Therefore, the Degree is 4. ($Degree\; =\; 4$)
   • Cardinality: The cardinality is the number of rows in the table. There are 5 rows representing 5 different items. Therefore, the Cardinality is 5. ($Cardinality\; =\; 5$)

The UNION operation in relational database management systems (RDBMS) is used to combine the result sets of two or more SELECT statements. It merges rows from multiple tables into a single result set. A key characteristic of the UNION operation is that it automatically removes duplicate rows from the combined result.

Conditions for UNION:

• The tables involved must have the same number of columns.
• The corresponding columns in each table must have compatible data types. For example, you can combine a column of integers with another column of integers, or text with text.
• The order of the columns matters. The first column of the first SELECT statement is combined with the first column of the second SELECT statement, and so on.

Example:

Consider two tables, Employees and Contractors, both having columns EmpID and Name.

Employees Table:

Contractors Table:

To get a combined list of all unique employee and contractor IDs and their names, we can use the UNION operation:

SELECT EmpID, Name FROM Employees

UNION

SELECT EmpID, Name FROM Contractors;

The result of this UNION operation would be:

Notice that the row (101, Alice) appears only once in the result, as UNION removes duplicates.