In Memory Database

Problem

Implement basic SQL-like operations, such as select, where, join, etc., of an in-memory database.

Instructions

Assume the following data is stored in the in-memory database

departments

id	name
0	engineering
1	finance

users

id	department_id	name
0	0	Ian
1	0	John
2	1	Eddie
3	1	Mark

salaries

id	user_id	amount
0	0	100
1	1	150
2	1	200
3	3	200
4	3	300
5	4	400

Building the binary

For Linux and Mac users, you can use the included Makefile to compile and run the project.

# Compile only
make
# Compile and run
make run

For Windows Visual Studio users, a vcproj template is included. Alternatively you can compile and run with the included Makefile.vs in Developer Command Prompt:

# cd to project directory
# Compile only
nmake -f Makefile.vs
# Compile and run
nmake -f Makefile.vs run

First step

Please implement Select and Where in Table class. For the sake of simplicity, you can assume all operations will be passed valid parameters, and all values are of type string. You do not need to concern yourself with error handling for occurrences like selecting an arbitrary column from a non-existent table.

For example,

// should print
// id, department_id, name
// 1, 0, John
Table* filtered_table = db->GetTable("users")->Where("id", "1");
Table* projected_table = filtered_table->Select(
    ToVector((string[]) { "id", "department_id", "name" }));
projected_table->Print();

Second step

Please implement InnerJoin in Database class.

// should print
// users.name, departments.name
// Ian, engineering
// John, engineering
Table* table = db->InnerJoin(
    db->GetTable("users"),
    "department_id",
    db->GetTable("departments"),
    "id");
Table* filtered_table = table->Where("departments.name", "engineering");
Table* projected_table = filtered_table->Select(
    ToVector((string[]) { "users.name", "departmetns.name" }));
projected_table->Print();

Third step

Please implement LeftJoin, RightJoin and OuterJoin in Database class, and use empty string "" for the missing values.

// should print
// users.name, salaries.amount
// Ian, 100
// John, 150
// John, 200
// Mark, 200
// Mark, 300
// Eddie,
Table* table = db->LeftJoin(
    db->GetTable("users"),
    "id",
    db->GetTable("salaries"),
    "user_id");
Table* projected_table = table->Select(
    ToVector((string[]) { "users.name", "salaries.amount" }));
projected_table->Print();

// should print
// users.name, salaries.amount
// Ian, 100
// John, 150
// John, 200
// Mark, 200
// Mark, 300
//     , 400
Table* table = db->RightJoin(
    db->GetTable("users"),
    "id",
    db->GetTable("salaries"),
    "user_id");
Table* projected_table = table->Select(
    ToVector((string[]) { "users.name", "salaries.amount" }));
projected_table->Print();

// should print
// users.name, salaries.amount
// Ian, 100
// John, 150
// John, 200
// Mark, 200
// Mark, 300
// Eddie,
// , 400
Table* table = db->OuterJoin(
    db->GetTable("users"),
    "id",
    db->GetTable("salaries"),
    "user_id");
Table* projected_table = table->Select(
    ToVector((string[]) { "users.name", "salaries.amount" }));
projected_table->Print();