Implementation of a SQL Database system (with a focus on efficient object oriented design and queries)
This database system can handle a subset of the SQL language (selects, inserts, table creation, etc). The database also supports arithmetic operations, comparison operations, joins, and filters.
Run Main.java to test the functionality. This class simply gets queries from stdin, runs them against our database, and prints the results to stdout. Alternatively, you can simply create a new instance of class Database. To run a query against this database, simply call Database.transact(String query).
load teams
load records
load fans
These commands load these three tables from file into the database.
select * from teams where YearEstablished > 1960
This returns all teams in our database that were founded later than the year 1960.
select * from teams where YearEstablished > 1960 and Sport != 'eSports'
This returns all teams in our database that were founded later than the year 1960 that are not eSports teams.
select TeamName, Sport, Season, Wins, Losses, Ties from teams, records where Sport == 'NFL Football'
This query performs a natural join between the teams and records tables on the TeamName column. It then gives us the season records of all NFL Football teams in our database.
select TeamName, Sport, Season, Wins - Losses as WinDifference from teams, records where Sport == 'NFL Football' and WinDifference > 0
This query calculates the WinDifference (defined as # Wins - # Losses) for every NFL Team in our database, and then only returns those records where the team won more games than it lost.
The Database class is our main class that everything runs through. The query is passed into the database as a String. The database passes the query to the Parser class, which parses the query and then calls the appropriate function back in the database.
The database class owns a list of tables, and the SQL queries it processes operate on these tables. The implementation of the Table interface can be found in the table package. RCTable is a specific implementation of Table that stores its data in both Column and Row formats for speed.
Values stored in the database must all be of type Literal. The implementations of these types can be found in the literals package.
Operators take in two input literals and output a value. The ArithmeticOperator outputs a Literal while the ComparisonOperator outputs a Boolean. Operators are used to in order to filter selections or combine two columns together.