Mini-SQL-Engine

A Mini SQL Engine which runs a subset of queries using Command Line Interface.

Features

This mini SQL engine supports the following SQL query features:

• SELECT: Retrieve data from tables. Supports * for all columns and specific column selection.
• FROM: Specify tables to retrieve data from. Supports joining multiple tables.
• WHERE: Filter data based on conditions. Supports comparison operators (=, <, >, <=, >=) and logical operators (AND, OR).
• GROUP BY: Aggregate data based on one or more columns. Supports aggregate functions like SUM(), AVG(), MIN(), MAX(), and COUNT().
• ORDER BY: Sort the result set in ascending (ASC) or descending (DESC) order.
• DISTINCT: Retrieve unique values from a column.

How to Run

1. Prerequisites: Ensure you have Python 3 installed.

2. Setup Database Files:

   • The files/ directory contains metadata.txt and CSV files (table1.csv, table2.csv, table3.csv) which represent the database schema and data.
   • metadata.txt defines the tables and their columns.
   • The CSV files contain the actual data for each table.

3. Execute Queries: Run the SQLengine.py script from the command line, passing your SQL query as an argument.

   Example:

   python3 SQLengine.py "SELECT * FROM table1;"
   python3 SQLengine.py "SELECT A, B FROM table1 WHERE A > 10 AND B < 50;"
   python3 SQLengine.py "SELECT SUM(A) FROM table1 GROUP BY B;"
   python3 SQLengine.py "SELECT A, B FROM table1 ORDER BY A DESC;"
   python3 SQLengine.py "SELECT DISTINCT A FROM table1;"
   python3 SQLengine.py "SELECT table1.A, table2.B FROM table1, table2 WHERE table1.A = table2.A;"

Project Structure

• SQLengine.py: The main script containing the SQL parsing and execution logic.
• preprocessing.py: Handles reading metadata and CSV data to set up the in-memory database.
• error.py: Contains functions for displaying various error messages.
• files/:
  • metadata.txt: Defines the database schema (table names and column names).
  • table1.csv, table2.csv, table3.csv: CSV files containing the data for each table.
• 2020201082.sh: (Optional) A shell script that might contain example commands or setup instructions.
• files.zip: (Optional) A zip archive of the files/ directory.
• files1/: (Optional) Another directory possibly containing alternative or sample data/metadata.