next → ← prev Relational algebra is a procedural query language. It gives a step by step process to obtain the result of the query. It uses operators to perform queries. Types of Relational operation
1. Select Operation:- The select operation selects tuples that satisfy a given predicate.
- It is denoted by sigma (σ).
Where: σ is used for selection prediction
r is used for relation
p is used as a propositional logic formula which may use connectors like: AND OR
and NOT. These relational can use as relational operators like =, ≠, ≥, <, >, ≤. For example: LOAN Relation
| BRANCH_NAME | LOAN_NO | AMOUNT |
|---|
| Downtown
| L-17
| 1000
| | Redwood
| L-23
| 2000
| | Perryride
| L-15
| 1500
| | Downtown
| L-14
| 1500
| | Mianus
| L-13
| 500
| | Roundhill
| L-11
| 900
| | Perryride
| L-16
| 1300
|
Input: Output:
| BRANCH_NAME | LOAN_NO | AMOUNT |
|---|
| Perryride
| L-15
| 1500
| | Perryride
| L-16
| 1300
|
2. Project Operation:- This operation shows the list of those attributes that we wish to appear in the result. Rest of the attributes are eliminated from the table.
- It is denoted by ∏.
Where A1, A2, A3 is used as an attribute name of relation r. Example: CUSTOMER RELATION
| NAME | STREET | CITY |
|---|
| Jones
| Main
| Harrison
| | Smith
| North
| Rye
| | Hays
| Main
| Harrison
| | Curry
| North
| Rye
| | Johnson
| Alma
| Brooklyn
| | Brooks
| Senator
| Brooklyn
|
Input: Output:
| NAME | CITY |
|---|
| Jones
| Harrison
| | Smith
| Rye
| | Hays
| Harrison
| | Curry
| Rye
| | Johnson
| Brooklyn
| | Brooks
| Brooklyn
|
3. Union Operation:- Suppose there are two tuples R and S. The union operation contains all the tuples that are either in R or S or both in R & S.
- It eliminates the duplicate tuples. It is denoted by ∪.
A union operation must hold the following condition: - R and S must have the attribute of the same number.
- Duplicate tuples are eliminated automatically.
Example:DEPOSITOR RELATION
| CUSTOMER_NAME | ACCOUNT_NO |
|---|
| Johnson
| A-101
| | Smith
| A-121
| | Mayes
| A-321
| | Turner
| A-176
| | Johnson
| A-273
| | Jones
| A-472
| | Lindsay
| A-284
|
BORROW RELATION
| CUSTOMER_NAME | LOAN_NO |
|---|
| Jones
| L-17
| | Smith
| L-23
| | Hayes
| L-15
| | Jackson
| L-14
| | Curry
| L-93
| | Smith
| L-11
| | Williams
| L-17
|
Input: Output:
| CUSTOMER_NAME |
|---|
| Johnson
| | Smith
| | Hayes
| | Turner
| | Jones
| | Lindsay
| | Jackson
| | Curry
| | Williams
| | Mayes
|
4. Set Intersection:- Suppose there are two tuples R and S. The set intersection operation contains all tuples that are in both R & S.
- It is denoted by intersection ∩.
Example: Using the above DEPOSITOR table and BORROW table Input: Output:
5. Set Difference:- Suppose there are two tuples R and S. The set intersection operation contains all tuples that are in R but not in S.
- It is denoted by intersection minus (-).
Example: Using the above DEPOSITOR table and BORROW table Input: Output:
| CUSTOMER_NAME |
|---|
| Jackson
| | Hayes
| | Willians
| | Curry
|
6. Cartesian product- The Cartesian product is used to combine each row in one table with each row in the other table. It is also known as a cross product.
- It is denoted by X.
Example:EMPLOYEE
| EMP_ID | EMP_NAME | EMP_DEPT |
|---|
| 1
| Smith
| A
| | 2
| Harry
| C
| | 3
| John
| B
|
DEPARTMENT
| DEPT_NO | DEPT_NAME |
|---|
| A
| Marketing
| | B
| Sales
| | C
| Legal
|
Input: Output:
| EMP_ID | EMP_NAME | EMP_DEPT | DEPT_NO | DEPT_NAME |
|---|
| 1
| Smith
| A
| A
| Marketing
| | 1
| Smith
| A
| B
| Sales
| | 1
| Smith
| A
| C
| Legal
| | 2
| Harry
| C
| A
| Marketing
| | 2
| Harry
| C
| B
| Sales
| | 2
| Harry
| C
| C
| Legal
| | 3
| John
| B
| A
| Marketing
| | 3
| John
| B
| B
| Sales
| | 3
| John
| B
| C
| Legal
|
7. Rename Operation:The rename operation is used to rename the output relation. It is denoted by rho (ρ). Example: We can use the rename operator to rename STUDENT relation to STUDENT1. Note: Apart from these common operations Relational algebra can be used in Join operations.
Next TopicDBMS Join
Operation ← prev next →
Which operation combines tuples from two relations?
Join finds the common tuple in the relations and combines it.
Which operation includes the tuples that are in both the relations?
Set Intersection:
The set intersection operation contains all tuples that are in both R & S. It is denoted by intersection ∩.
Which operation combines the tuples of one relation with all the tuples of the other relation?
The Cartesian Product is also an operator which works on two sets. It is sometimes called the CROSS PRODUCT or CROSS JOIN. It combines the tuples of one relation with all the tuples of the other relation.
Which operation allows the combining of two relation?
Explanation: Union just combines all the values of relations of same attributes.
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