1 Project Overview In computer science, a “database” is an organized collection of data that allows for easy access,
management, and updating. It’s essentially a storage system where you can keep large amounts of
information, such as student records, product inventories, or customer information. The most
popular type of databases is relational, where the data is organized as tables.
Your Task. In this project, you will implement a mini-database management system (i.e.,
miniDB) that supports creating tables, updating records, querying tables, and more. Your system
should be able to process commands in our simplified version of SQL (i.e., miniSQL) and
output the query results.
What is SQL? SQL (Structured Query Language) is a standard language for managing and
manipulating relational databases, enabling users to create, read, update, and delete data, as well
as define and modify database structures. Here, you’ll work with a simplified version of SQL
designed specifically for our miniDB.
How a table in our miniDB looks like? Table 1 shows a table used in our mini database. Each row is a “record,” and each column is a “field.” Your database needs to manage multiple tables. Table 1: A table showing student information ID Name GPA Major 1000 Jay Chou 3.0 Microelectronics 1001 Taylor Swift 3.2 Data Science 1002 Bob Dylan 3.5 Financial Technology Usage of minidb Compile your program into a single executable named minidb, which accepts two command-line arguments: the first is the input SQL file, and the second is the output file. The basic usage format of the program is as follows: ./minidb input.sql output.txt 2 Syntax of miniSQL 2.1 Create Database and Use Database A database contains multiple tables. Before operating on specific table, the user has to specify the database they want to use. Your mini-database system will support basic database management with “CREATE DATABASE” and “USE DATABASE” commands. Page 2 Create Database The user can create a database using the following syntax: CREATE DATABASE database_name; Your minidb should be able to create a database. Before exiting minidb, your program should store all the current table content in files to disks. Before doing anything regarding to the tables (query, update, delete, etc.), the user must specifiy which database they want to operate on. This step is done by “USE DATABASE” statement: Use Database The “USE DATABASE” command is used to switch to a specific database, so any subsequent commands (like creating tables, inserting data, or querying) will apply to the selected database. USE DATABASE database_name; 2.2 Create Tables In this project, minidb will support a simplified CREATE TABLE command with three data types: FLOAT, TEXT, and INTEGER. This command allows users to define a table by specifying its name and columns. Each column must have a unique name and one of the three supported data types. Syntax CREATE TABLE table_name ( column1_name column1_type, column2_name column2_type, column3_name column3_type, ... ); This example creates a table named table name with three columns: column1 name, which holds floating-point numbers; column2 name, which holds text values; and column3 name, which holds integer values. Examples if the user wants to create a table the same as Table 1, the user needs to input the following create table command: CREATE TABLE student ( ID INTEGER, Name TEXT, GPA FLOAT, Major TEXT ); 2.3 Drop Tables In this project, minidb will also support a simplified DROP TABLE command, which allows users to delete a table and all its associated data from the database. Once a table is dropped, all data in that table is permanently removed, and any queries referencing the deleted table will fail. This command is useful for freeing up database space or removing outdated or unneeded tables. Page 3 Syntax DROP TABLE table_name; This example removes the table named table name from the database, along with all data stored within it. Examples If the user wants to delete a table named student, the user would input the following DROP TABLE command: DROP TABLE student; This command permanently removes the student table and all its data, ensuring it can no longer be accessed or queried in minidb. 2.4 Data Insertion After creating a table with the CREATE TABLE command, you can insert a record into it using the INSERT INTO command. This command specifies the table name, followed by a list of column values in the same order as they were defined in the table schema. Syntax INSERT INTO table_name VALUES (value1, value2, ...); Examples To insert the data shown in the student table created above, you would use: INSERT INTO student VALUES (1000, ’Jay Chou’, 3.0, ’Microelectronics’); INSERT INTO student VALUES (1001, ’Taylor Swift’, 3.2, ’Data Science’); INSERT INTO student VALUES (1002, ’Bob Dylan’, 3.5, ’Financial Technology’); Each INSERT INTO command adds one row of data to the table, with values corresponding to the columns defined in CREATE TABLE. 2.5 Data Query: Basics Suppose you have a student table with the following columns and data: ID Name GPA Major 1000 Jay Chou 3.0 Microelectronics 1001 Taylor Swift 3.2 Data Science 1002 Bob Dylan 3.5 Financial Technology Syntax SELECT column1, column2, ... FROM table_name; Page 4 Examples Suppose you have the student table like Table 1.

1. Selecting Specific Columns: If you want to retrieve only the Name and GPA columns of all students, you would use: SELECT Name, GPA FROM student; Result: Name GPA Jay Chou 3.0 Taylor Swift 3.2 Bob Dylan 3.5
2. Selecting All Columns: To retrieve all columns in the table, you can use the * symbol: SELECT * FROM student; Result: ID Name GPA Major 1000 Jay Chou 3.0 Microelectronics 1001 Taylor Swift 3.2 Data Science 1002 Bob Dylan 3.5 Financial Technology This simple selection retrieves rows from the student table based on the specified columns, showing just the data you need. Any order of the rows is acceptable. 2.6 Data Query: “Where” Clause The WHERE clause in minidb allows you to filter records based on specific conditions, using basic comparison operators and logical connectors. In this simplified version, the WHERE clause supports only the following conditions: • Comparisons: column > value, column < value, column = value • Logical Connectors: AND and OR to combine multiple conditions Syntax for WHERE SELECT column1, column2 FROM table_name WHERE condition1 AND/OR condition2; Examples Suppose you have the student table:
3. Single Condition: To retrieve names of students with a GPA greater than 3.0, you would use: SELECT Name FROM student WHERE GPA > 3.0; Page 5 ID Name GPA Major 1000 Jay Chou 3.0 Microelectronics 1001 Taylor Swift 3.2 Data Science 1002 Bob Dylan 3.5 Financial Technology Result: Name Taylor Swift Bob Dylan
4. Multiple Conditions with AND: To find students with a GPA greater than 3.0 who are also majoring in Data Science, use: SELECT Name FROM student WHERE GPA > 3.0 AND Major = ’Data Science’; Result: Name Taylor Swift
5. Multiple Conditions with OR: To retrieve students with a GPA less than 3.1 or majoring in Financial Technology, use: SELECT Name FROM student WHERE GPA < 3.1 OR Major = ’Financial Technology’; Result: Name Jay Chou Bob Dylan By using WHERE with supported comparison operators and logical connectors, you can retrieve data based on specific conditions, making your queries both flexible and efficient. 2.7 Data Query: “Inner Join” Clause An INNER JOIN connects records from two tables based on a specified condition. When we INNER JOIN Table A’s X column with Table B’s Y column, each record in Table A is matched with a record in Table B if the value in Table A’s X column is equal to the value in Table B’s Y column. Page 6 Only pairs of records that meet this condition are included in the result, forming a combined view of related data from both tables. In other words, the INNER JOIN condition effectively links records from Table A and Table B wherever there is a match between Table A’s X and Table B’s Y. Syntax SELECT table1.column1, table2.column1 FROM table1 INNER JOIN table2 ON table1.X = table2.Y; The INNER JOIN clause connects records from two tables based on a matching condition between columns. When we use INNER JOIN on Table A’s X column and Table B’s Y column, each record in Table A is paired with records in Table B where values in X and Y are equal. Only records that satisfy this condition are included in the result, which provides a combined view of related data from both tables. When using INNER JOIN to combine data from multiple tables, it’s essential to specify which table each column belongs to by using the table name followed by a dot, and then the column name. This is called a fully qualified column name and helps avoid ambiguity, especially when both tables have columns with the same name. For example, if both student and course enrollment tables have a column named StudentID, using student.StudentID and course enrollment.StudentID makes it clear which table each column comes from. Examples Suppose you have two tables, student and course enrollment, as follows: StudentID Name 1 Jay Chou 2 Taylor Swift 3 Bob Dylan 4 Omnipotent Youth Society Table 2: student table To retrieve each student’s name along with the courses they are enrolled in, we can INNER JOIN the student and course enrollment tables on the StudentID column: SELECT student.Name, course_enrollment.Course FROM student INNER JOIN course_enrollment ON student.StudentID = course_enrollment.StudentID; Page 7 StudentID Course 1 Microelectronics 2 Data Science 2 Machine Learning 3 Financial Technology 4 Mathematics Table 3: course enrollment table Name Course Jay Chou Microelectronics Taylor Swift Data Science Taylor Swift Machine Learning Bob Dylan Financial Technology Omnipotent Youth Society Mathematics Result: In this example, the result includes every matched pair where StudentID values are equal in both tables, showing each student’s name alongside their enrolled courses. With INNER JOIN, each match between student and course enrollment based on StudentID results in a row in the final output, showing how INNER JOIN combines related data across tables. 2.8 Data Update The UPDATE command in SQL is used to modify existing records in a table. In minidb, the UPDATE command allows you to change values in specific columns based on a condition specified with the WHERE clause. This helps ensure that only certain rows are updated, rather than modifying every row in the table. Syntax for UPDATE The general syntax for using UPDATE is as follows: UPDATE table_name SET column1 = new_value1, column2 = new_value2, ... WHERE condition; • table name: The name of the table where records will be updated. • SET: Specifies the columns to update and their new values. • WHERE: (Optional) Specifies a condition to determine which rows to update. Without WHERE, all rows in the table will be updated. Examples Suppose you have a student table:
6. Updating a Specific Row: If you want to update Jay Chou’s GPA to 3.6, you can specify a WHERE condition to target only his record: Page 8 ID Name GPA 1000 Jay Chou 3.0 1001 Taylor Swift 3.2 1002 Bob Dylan 3.5 Table 4: student table UPDATE student SET GPA = 3.6 WHERE Name = ’Jay Chou’; Result: ID Name GPA 1000 Jay Chou 3.6 1001 Taylor Swift 3.2 1002 Bob Dylan 3.5
7. Updating Multiple Rows: To increase the GPA of all students with a GPA less than 3.5 by 0.1, use the following command: UPDATE student SET GPA = GPA + 0.1 WHERE GPA < 3.5; Result: ID Name GPA 1000 Jay Chou 3.6 1001 Taylor Swift 3.3 1002 Bob Dylan 3.5 In this example, only records meeting the WHERE condition are updated, which makes the UPDATE command powerful for targeted changes. Without a WHERE clause, all rows in the table would be updated with the new values specified. 2.9 Data Deletion The DELETE command in SQL is used to remove records from a table. Similar to UPDATE, the DELETE command can use the WHERE clause to specify conditions, allowing you to delete only certain rows rather than all rows in the table. Syntax for DELETE The general syntax for using DELETE is as follows: Page 9 DELETE FROM table_name WHERE condition; • table name: The name of the table from which records will be deleted. • WHERE: (Optional) Specifies a condition to determine which rows to delete. Without WHERE, all rows in the table will be deleted. Example of DELETE with WHERE Suppose you want to delete records of students with a GPA less than 3.0 in a student table: DELETE FROM student WHERE GPA < 3.0; Only rows meeting the WHERE condition will be deleted. Without a WHERE clause, all rows in the student table would be removed. 3 Format of the Output Each query (SELECT statement) result will be printed in a CSV format with the following rules:
8. Output Format: Each result is printed in CSV format, where fields are separated by commas.
9. Header Row: The first row of the output will contain the column names, also separated by commas. 3. Text Fields: Text fields are enclosed in double quotes (""). There will be no text fields containing double quotes in the data, so no further formatting is necessary. 4. Numeric Fields: • Integer fields are printed as-is. • Float fields are printed with exactly two decimal places, rounded if necessary. minidb executes the following SELECT query: SELECT ID, Name, GPA FROM student; and returns the following data: ID Name GPA 1000 Jay Chou 3.00 1001 Taylor Swift 3.20 1002 Bob Dylan 3.50 The output in CSV format would be: ID,Name,GPA 1000,"Jay Chou",3.00 1001,"Taylor Swift",3.20 1002,"Bob Dylan",3.50 Page 10 3.1 Example 1 Here’s an example input.sql and the corresponding output.csv based on the simplified miniSQL format. input.sql CREATE DATABASE db_university; USE DATABASE db_university; CREATE TABLE student ( ID INTEGER, Name TEXT, GPA FLOAT ); INSERT INTO student VALUES (1000, ’Jay Chou’, 3.0); INSERT INTO student VALUES (1001, ’Taylor Swift’, 3.2); INSERT INTO student VALUES (1002, ’Bob Dylan’, 3.5); SELECT ID, Name, GPA FROM student; SELECT ID, Name, GPA FROM student WHERE GPA > 3.1; output.csv ID,Name,GPA 1000,"Jay Chou",3.00 1001,"Taylor Swift",3.20 1002,"Bob Dylan",3.50

ID,Name,GPA 1001,"Taylor Swift",3.20 1002,"Bob Dylan",3.50 In this output.csv: • Each query result is separated by a line (---) to clearly differentiate outputs from consecutive queries. • Text fields are surrounded by double quotes, while integers and floats are printed directly, with floats formatted to two decimal places. Page 11 3.2 Example 2 After executing Example 1, minidb should serialize the information of db unversity in disks. Now, when minidb reads a SQL statement “use database”, it needs to load previous database content. Here’s an example input2.sql and the corresponding output2.csv based on the simplified miniSQL format. input2.sql USE DATABASE db_university; SELECT ID, Name, GPA FROM student WHERE GPA > 3.1; output2.csv ID,Name,GPA 1001,"Taylor Swift",3.20 1002,"Bob Dylan",3.50 4 Error Report minidb should be able to check the syntax of miniSQL, and report the line number where the error happens.