Sql Query Parser

input.txt

2
Students
Name Rollno* Hall Mobile
Kush 10MF100021 Azad 944641684
Nithish 10MA20028 Azad 95426546
Mandula 10MF10013 Azad 7501654369
Ajit 10MA20014 RP 7797256805
Kai 10NA300214 MS 9800165458
Departments
Name* Departments
Kush Mech
Nithish Maths
Ajit Maths
Mandula Mech

SQLQuery.java

import java.io.*;

public class SQLquery {

	int noOfTables;
	Table[] tables;
	String row;
	BufferedReader br1 = new BufferedReader(new InputStreamReader(System.in));

	void readFile() {
		int tempTableCount = 0;
		try {
			BufferedReader br = new BufferedReader(new FileReader("input.txt"));
			noOfTables = Integer.parseInt(br.readLine());
			tables = new Table[noOfTables];
			while (tempTableCount < noOfTables) {
				tables[tempTableCount] = new Table(br.readLine());
				tables[tempTableCount].columnNames = br.readLine().split(" ");
				int i = 0;
				while ((row = br.readLine()) != null && row.contains(" ")) {
					br.mark(1000);
					tables[tempTableCount].tableData[i] = row.split(" ");
					tables[tempTableCount].noOfColumns = tables[tempTableCount].tableData[i].length;
					i++;
				}
				tables[tempTableCount].noOfRows = i;
				if (row != null) {
					br.reset();
				}
				tables[tempTableCount].getKey();
				tempTableCount++;
			}
			br.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	void writeFile() {
		try {
			BufferedWriter bw = new BufferedWriter(new FileWriter("output.txt"));
			bw.write(noOfTables);
			bw.newLine();
			for (int i = 0; i < noOfTables; i++) {
				bw.write(tables[i].tableName);
				bw.newLine();
				bw.write(tables[i].columnNames[1]);
				bw.newLine();
			}
			bw.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	void input() {
		String query;
		try {
			do {
				System.out.println("Enter the SQL query in caps");
				query = br1.readLine();
				if (query.contains("INSERT")) {
					insertInto(query);
				} else if (query.contains("DELETE"))
					deleteFrom(query);
				else if (query.contains("SELECT"))
					selectWhere(query);
				else if (query.contains("DISPLAY"))
					displayTable(query);
				else if (query.contains("JOIN"))
					joinTables(query);
				else if (query.contains("CROSSPRODUCT"))
					crossProduct(query);

			} while (!query.equalsIgnoreCase("EXIT"));
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	void insertInto(String query) {
		// Syntax is INSERT INTO table_name VALUES (value1,value2,value3)
		String tableName = query.substring(12);
		tableName = tableName.substring(0, tableName.indexOf(" "));
		try {
			String[] values = query.substring(query.indexOf("(") + 1,
					query.indexOf(")")).split(",");
			for (int j = 0; j < noOfTables; j++) {
				if (tableName.equalsIgnoreCase(tables[j].tableName)) {
					for (int i = 0; i < tables[j].columnNames.length; i++) {
						tables[j].tableData[(tables[j].noOfRows)][i] = values[i];
					}
					tables[j].noOfRows++;
					printTable(j);
				}
			}

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

	void deleteFrom(String query) {
		// Syntax is DELETE FROM table_name WHERE columnname=some_value
		String value = null, columnid = null;
		String tableName = query.substring(12);
		tableName = tableName.substring(0, tableName.indexOf(" "));
		columnid = query.substring(12 + tableName.length() + 1 + 5 + 1,
				query.indexOf("="));
		value = query.substring(query.indexOf("=") + 1);
		try {
			for (int i = 0; i < noOfTables; i++) {
				if (tableName.equalsIgnoreCase(tables[i].tableName)) {
					for (int j = 0; j < tables[i].noOfRows; j++) {
						if (tables[i].tableData[j][tables[i]
								.getColumnId(columnid)].equalsIgnoreCase(value)) {
							tables[i].tableData = removeRow(
									tables[i].tableData, j, tables[i].noOfRows,
									tables[i].noOfColumns);
							tables[i].noOfRows--;
						}
					}
					printTable(i);
				}
			}

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

	void printTable(int id) {
		for (int i = 0; i < tables[id].noOfRows; i++) {
			for (int j = 0; j < tables[id].noOfColumns; j++) {
				System.out.print(tables[0].tableData[i][j] + " ");
			}
			System.out.println("");
		}
	}

	void selectWhere(String query) {
		// Syntax SELECT WHERE FROM tablename id=value
		String temp = query.substring(query.indexOf("FROM") + 5);
		String temp1 = temp.substring(temp.indexOf(" ") + 1);
		String tableName = temp.substring(0, temp.indexOf(" "));
		String id = temp1.substring(0, temp1.indexOf("="));
		String value = temp1.substring(temp1.indexOf("=") + 1);
		int p = 0, q = 0;

		for (int i = 0; i < noOfTables; i++) {
			if (tables[i].tableName.equalsIgnoreCase(tableName)) {

				p = i;
				for (int j = 0; j < tables[i].columnNames.length; j++) {
					if (tables[i].columnNames[j].equalsIgnoreCase(id)) {

						q = j;

					}
				}
			}
		}
		for (int i = 0; i < tables[p].noOfRows; i++) {
			if (tables[p].tableData[i][q].equalsIgnoreCase(value)) {
				for (int j = 0; j < tables[p].noOfColumns; j++) {
					System.out.print(tables[p].tableData[i][j] + " ");
				}
				System.out.println();
			}
		}

	}

	void displayTable(String query) {
		// Syntax is DISPLAY tablename
		String tableName = query.substring(query.indexOf(" ") + 1);
		for (int i = 0; i < noOfTables; i++) {
			if (tables[i].tableName.equalsIgnoreCase(tableName)) {
				printTable(i);
				break;
			}
		}

	}

	void joinTables(String query) {
		// JOIN table1 table2
		String tableName1, tableName2, temp;
		int p = 0, q = 0, r = 0, s = 0;
		String[][] tempa = new String[100][20];
		temp = query.substring(5);
		tableName1 = temp.substring(0, temp.indexOf(" "));
		tableName2 = temp.substring(temp.indexOf(" ") + 1);
		for (int i = 0; i < noOfTables; i++) {
			if (tables[i].tableName.equalsIgnoreCase(tableName1)) {
				p = i;
			}
			if (tables[i].tableName.equalsIgnoreCase(tableName2)) {
				q = i;
			}
		}
		for (int i = 0; i < tables[p].columnNames.length; i++) {
			for (int j = 0; j < tables[q].columnNames.length; j++) {
				if (tables[p].columnNames[i]
						.equalsIgnoreCase(tables[q].columnNames[j])) {
					r = i;
					s = j;
					break;
				}
			}
		}
		for (int i = 0; i < tables[p].noOfRows; i++) {
			for (int j = 0; j < tables[q].noOfRows; j++) {
				for (int k = 0; k < tables[p].noOfColumns
						+ tables[q].noOfColumns; k++) {
					if (k < tables[p].noOfColumns) {
						tempa[(tables[q].noOfRows * i) + j][k] = tables[p].tableData[i][k];
					} else {
						tempa[(tables[q].noOfRows * i) + j][k] = tables[q].tableData[j][k
								- tables[p].noOfColumns];
					}
				}
			}
		}
		for (int i = 0; i < (tables[p].noOfRows * tables[q].noOfRows); i++) {
			if (tempa[i][r].equals(tempa[i][s + tables[p].noOfColumns])) {
				for (int j = 0; j < tables[p].noOfColumns
						+ tables[q].noOfColumns; j++) {
					System.out.print(tempa[i][j] + " ");
				}
				System.out.println();
			}
		}
	}

	void crossProduct(String query) {
		// Syntax is CROSSPRODUCT table1 table2
		String tableName1, tableName2, temp;
		int p = 0, q = 0;
		String[][] tempa = new String[100][20];
		temp = query.substring(13);
		tableName1 = temp.substring(0, temp.indexOf(" "));
		tableName2 = temp.substring(temp.indexOf(" ") + 1);
		for (int i = 0; i < noOfTables; i++) {
			if (tables[i].tableName.equalsIgnoreCase(tableName1)) {
				p = i;
			}
			if (tables[i].tableName.equalsIgnoreCase(tableName2)) {
				q = i;
			}
		}
		for (int i = 0; i < tables[p].noOfRows; i++) {
			for (int j = 0; j < tables[q].noOfRows; j++) {
				for (int k = 0; k < tables[p].noOfColumns
						+ tables[q].noOfColumns; k++) {
					if (k < tables[p].noOfColumns) {
						tempa[(tables[q].noOfRows * i) + j][k] = tables[p].tableData[i][k];
					} else {
						tempa[(tables[q].noOfRows * i) + j][k] = tables[q].tableData[j][k
								- tables[p].noOfColumns];
					}
				}
			}
		}
		for (int i = 0; i < (tables[p].noOfRows * tables[q].noOfRows); i++) {
			for (int j = 0; j < tables[p].noOfColumns + tables[q].noOfColumns; j++) {
				System.out.print(tempa[i][j] + " ");
			}
			System.out.println();
		}
	}

	String[][] removeRow(String[][] a, int rowid, int rowsize, int columnsize) {
		String[][] temp = new String[100][10];
		int p = 0;
		try {
			for (int i = 0; i < rowsize; i++) {
				if (i != rowid) {
					for (int j = 0; j < columnsize; j++) {
						temp[p][j] = a[i][j];
					}
					p++;
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		return temp;
	}

	public static void main(String args[]) {
		SQLquery sq = new SQLquery();
		sq.readFile();
		sq.input();
	}

}

class Table {
	String tableName;
	String[] columnNames;
	String key;
	int keyValue;
	String[][] tableData = new String[100][10];
	int noOfRows;
	int noOfColumns;

	Table(String tableName) {
		this.tableName = tableName;

	}

	void getKey() {
		for (int i = 0; i < columnNames.length; i++) {
			if (columnNames[i].contains("*")) {
				key = columnNames[i].replace("*", "");
				keyValue = i;
			}

		}
	}

	int getColumnId(String id) {
		int temp = 0;
		for (int i = 0; i < columnNames.length; i++) {
			if (columnNames[i].equalsIgnoreCase(id)) {
				temp = i;
			}
		}
		return temp;
	}

}