Implementation of Relational Algebra functions

---

Aim of the Project

To write a program in C++ to implement Relational Algebra functions present in DBMS.

---

Functions implemented

The program implements the following Relational Algebra functions:

1. SELECT

2. PROJECT

3. RENAME

4. UNION

5. SET DIFFERENCE

6. CARTESIAN PRODUCT

---

Project Details

The program assumes the following:

• The database folder is present in the same directory as the main project file
• The database folder has a db_info.txt file containing the details of the database
• The database folder has a tables subdirectory which contains all table files in space separated form in .txt format
• The tables have their schema in the top three lines:
  • First line has table name
  • Second line has column names
  • Third line has column data types
• The data in the files is valid:
  • There is no newline
  • All data has same number of columns (except) table name
  • The data types corresponding to the data are correct
• The data types allowed are:
  • int
  • float
  • varchar
• Comparison accross data types is not allowed
• Queries are delimited by a ;

---

Syntax

The basic syntax of the queries is as follows:

Show tables in database as specified in db_info.txt:

SHOW_TABLES;

SELECT:

SEL{predicate}(table_name);

PROJECT:

PRO{column_name1:column_name2}(table_name);

RENAME:

REN{new_table_name|column_name1:column_name2}(table_name);

UNION:

UNI(table_name1, table_name2);

SET DIFFERENCE:

DIF(table_name1, table_name2);

CARTESIAN PRODUCT:

CRP(table_name1, table_name2);

EXIT:

EXIT;

The predicate syntax for SEL:

SEL{(a > b | c = d) & e ! f}(table_name);

The available operators are:

1. + : Add two ints or floats
2. - : Subtract two ints or floats
3. * : Multiply two ints or floats
4. / : Divide two ints or floats
5. = : Compare two operands, TRUE if equal
6. ! : Compare two operands, TRUE if unequal
7. > : Compare two operands, TRUE if former is greater than latter
8. < : Compare two operands, TRUE if former is lesser than latter
9. & : Logical AND
10. | : Logical OR

NOTES:

• Comparison between different data types is not allowed

• varchar (Strings) are enclosed in '

• float operands must have a .

• Invalid operands are not allowed

The predicate syntax for PRO:

PRO{a:b:c:d}(table_name);

NOTES:

• Column names must be separated by a :

• Column names must be present in table

• Column names are displayed in given order

The predicate syntax for REN:

REN{new_table_name|a:b:c:d}(table_name);
REN{new_table_name}(table_name);

NOTES:

• Table name and column names must be separated by a |

• Column names must be separated by a :

• Column names must be valid

• Column names are renamed in given order

• If no column names are provided, the colum names are retained

• Either all or none of the column names must be provided

---

Sample Queries

1. SEL{faculty.salary > 80000 & dept = 'CSE'}(faculty);
2. PRO{id:name:grade}(studuent);
3. UNI(PRO{name}(faculty), PRO{name}(student));
4. DIF(PRO{name}(faculty), PRO{name}(student));
5. CRP(student, course);
6. REN{stud|stud_id:name:cgpa}(student);

For more queries, see Query file

---

Comments:

• Syntax errors are not allowed
• SELECT takes exactly one predicate
• RENAME cannot rename to a table already present
• Column and table names must be alphanumeric
• Invalid comparisons between data types are not allowed
• UNI and DIF operations must have same column names and data types. Order need not be same
• Nested queries are allowed
• CRP operation needs different column names
• PRO should have unique column names
• All whitespaces are ignored

---