Mini SQL Engine

A mini sql engine which can run a subset of SQL queries using command line interface.

Dataset:

1. csv files for tables.
   • If a file is : File1.csv , the table name should be File1
   • There should be no tab separation or space separation, but the values can be in double quotes or without quotes.
2. All the elements in files should be integers.
3. A file named: metadata.txt should be given which will have the following structure for each table:

    <table_name>
    <attribute 1>
    ..
    ..
    <attribute N>
    <end_table>
   

4. Column names should be unique among all the tables. So column names should not​ preceded by table names in SQL queries.

Type of Queries

The the following set of queries are supported:

1. Project​ Columns(could be any number of columns) from one or more tables :
   • Select * from table_name;
   • Select col1, col2 from table_name;
2. Aggregate functions​: Simple aggregate functions on a single column. Sum, average, max, min and count.
   • Select max(col1) from table_name;
3. Select/project with ​distinct​ from one table: (distinct of a pair of values indicates the pair should be distinct)
   • Select distinct col1, col2 from table_name;
4. Select with ​WHERE​ from one or more tables :
   • Select col1,col2 from table1,table2 where col1 = 10 AND col2 = 20;
   • In the where queries, there should be a maximum of one AND/ORoperator with no NOT operators.
   • Relational operators that are to be handled in the assignment, the operators include "< , >, <=, >=, =".
5. Select/Project Columns(could be any number of columns) from table using “​group by​”:
   • Select col1, COUNT(col2) from table_name group by col1.
   • In the group by queries, Sum/Average/Max/Min/Count can be used as aggregate functions.
6. Select/Project Columns(could be any number of columns) from table in ascending/descending order according to a column using “​order by”​:
   • Select col1,col2 from table_name order by col1 ASC|DESC.
   • At max only one column can be used to sort the rows.
   • Query can have multiple tables

Format of Input :

python3 sql_engine.py "<SQL Query>"

Format of Output :

<Table1.column1,Table1.column2,...TableN.columnM>
                    Row 1 
                    Row 2 
                    ....... 
                    Row N