simple-ra

A simple implementation of Relational Algebra.

Compiling and running

Go to the directory, and just use make to compile and ./simple_ra or make run to run. The package libreadline (libreadline-devel or libreadline-dev) is required to compile and run the program. You can install it using the package manager of your operating system.

Syntax

The syntax is totally inspired from pure RA. However, to make it easier to type using an ASCII keyboard, some changes have been made. Below is a brief description of the syntax.

• table_name; : Displays whole view/table from a view/table named table_name

• SELECT [predicate] (expression); : Select using a predicate from expression. Predicate is a list of elementary boolean expressions. The following predicate expressions are valid. The predicate expression is right associative and precedence of && and || is the same.

value > value

value >= value

value < value

value <= value

value = value

value =/= value

value > 4 && value < 3

!(value > 4 && value < 3) || greeting =/= "Hello"

Here, a value is either a column name or a value. Operating on two values of different type will result in an error.

• PROJECT [comma_seperated_column_names] (expression); : Project said columns from the expression.

PROJECT [s_id, name] (student);

• RENAME [comma_seperated_column_names] (expression); : Rename said columns from the expression.

• AGGREGATE [function : column] (expression); : Run the aggregate function function on the column column. The following functions are built-in

MAX : column_name

MIN : column_name

SUM : column_name, here column name should be of numeric type

AVG : column_name, here column name should be of numeric type

COUNT : column_name, displays the count of each value in the relation.

• expression * expression; : Cartesian product

• expression + expression; : Union

• expression ^ expression; : Intersection

• expression @ expression; : Natural join

• expression - expression; : Set difference

• [view_name] ~ expression; : Create a view with the identifier view_name.

• [table_name] <- expression; : Store the relation with name table_name in the database.

The binary operations are right associative and precedence of all operations is the same.

Example

Some example queries have been given below.

[student] <- RENAME [s_id, f_name, l_name, dept_id] ({1, "Shubham", "Chaudhary", 1});

[student] <- student ^ {2, "Shivam", "Garg", 1};

SELECT [s_id > 3 && f_name =/= "Shubham"] (student);

student @ department;

[marks] <- RENAME [s_id, eng, phy] ({1, 98.0, 95.0});

[marks] <- marks + {3, 98.1, 92.0};

PROJECT [AVG : eng] (marks);

[min_eng] ~ PROJECT [s_id] (marks @ RENAME [eng] (marks));

Explanation: It then assigns the min_eng with the view containing the s_ids of the students with minimum marks in eng.

student @ min_eng @ department; will give all the details of the student with minimum marks in english. The result of the query will change in accordance with the original data.

Other queries have been given in file queries.sra. Formal syntax is defined in EBNF form in syntax.ebnf.

Helper Commands

The following utility commands are available

:quit; : Quit the program

:help; : Show program help

:drop table_ name; : Drop the table with specified name

:showall; : Show the basic information of the whole database, i.e the schema and no. of tuples of all tables and description of all views.