C# – Make your own query language

Posted on February 28, 2015 by

Well, most probably the answer depends on the query language 🙂

Here is the task:

Problem 3 – A query language over a CSV file

A CSV files (comma separated values) can be represented as a table.

For example this CSV file:

id, name, course
1, Rado, Haskell
2, Ivo, Python

id, name, course

1, Rado, Haskell

2, Ivo, Python

Can be represented by this table:

id	name	course
1	Rado	Haskell

We are going to use CSV files as tables and make a simple query language for fetching data.

In a language of your choice, make a program that:

Reads a CSV file.
Gives the user an interactive input for queries.
Answers the queries with data from the CSV file.

The queries, that should be supported are:

SELECT [columns] LIMIT X – where you can SELECT without giving the LIMIT. Then this will fetch all rows.
SUM [column] – returns the sum of all integers in the given column.
SHOW – returns a list of all column names in your data.
FIND X – returns all rows, that has X in some of their cells (Match X with at least one of the columns). If X is a string, search for every string, that contains X as a substring.

Here are examples of all queries.

Consider that we have loaded the following CSV:

id,name,hometown
1,Kiara,Lunel
2,Mona,Henley-on-Thames
3,Kiayada,Villers-aux-Tours
4,Karly,Hillsboro
5,Igor,Oranienburg

id,name,hometown

1,Kiara,Lunel

2,Mona,Henley-on-Thames

3,Kiayada,Villers-aux-Tours

4,Karly,Hillsboro

5,Igor,Oranienburg

Now, let’s make queries:

query&gt;SELECT id
|id|
|--|
|1 |
|2 |
|3 |
|4 |
|5 |

query>SELECT id

|id|

|--|

|1 |

|2 |

|3 |

|4 |

|5 |

query&gt; SELECT id, name
|id| name   |
|--|--------| 
|1 |Kiara   |
|2 |Mona    |
|3 |Kiayada |
|4 |Karly   |
|5 |Igor    |

query> SELECT id, name

|id| name |

|--|--------|

|1 |Kiara |

|2 |Mona |

|3 |Kiayada |

|4 |Karly |

|5 |Igor |

query&gt; SELECT id, name LIMIT 1
|id| name   |
|--|--------| 
|1 |Kiara   |

query> SELECT id, name LIMIT 1

|id| name |

|--|--------|

|1 |Kiara |

query&gt; SUM id
15

query> SUM id

query&gt; SHOW
id, name, hometown

query> SHOW

id, name, hometown

query&gt; FIND "-"
|id| name   | hometown          |
|--|--------| ------------------|
|2 |Mona    | Henley-on-Thames  |
|3 |Kiayada | Villers-aux-Tours |

query> FIND "-"

|id| name | hometown |

|--|--------| ------------------|

|2 |Mona | Henley-on-Thames |

|3 |Kiayada | Villers-aux-Tours |

Features

If the query is non-valid – say it. Don’t crash the program.
As you see in the examples, the results should be displayed in visual, tabular way. This is up to you. You don’t have to follow the styles of the example.

What I did? Check by yourself:

And my favourite – here comes the code 🙂

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Text.RegularExpressions;

class CSV_query_language
{
    public static string[] sCommandActivate;
    public static string[] sCommandDetails;

    public const string SHOW = "show";
    public const string SUM = "sum";
    public const string FIND = "find";
    public const string SELECT = "select";
    public const string LIMIT = "limit";

    static void Main()
    {
        try
        {
            string sCommand = Console.ReadLine();
            sCommandActivate = sCommand.Split('>');
            sCommandDetails = sCommandActivate[1].Split(' ');

            if (sCommandDetails.Contains(SHOW))
            {
                ShowHeader();
            }

            if (sCommandDetails.Contains(SUM))
            {
                SumValues();
            }

            if (sCommandDetails.Contains(FIND))
            {
                FindTheResults();
            }
            if (sCommandDetails.Contains(SELECT))
            {
                ShowMeWhatYouGotGeneral();
            }
            Console.WriteLine("\nThank you for using the custom query language!\nPress Y for a new query.");
            string sNewQuery = Console.ReadLine();
            if (sNewQuery == "Y" || sNewQuery == "y")
            {
                Main();
            }
        }

        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);

            Console.WriteLine("\nAn error has occurred. Try again!");
            Console.WriteLine("Possible queries:\n");
            Console.WriteLine("query> show");
            Console.WriteLine("query> sum id");
            Console.WriteLine("query> select id, name, age limit 5");
            Console.WriteLine("query> select id, experience");
            Console.WriteLine("query> find \"-\"");
            Console.WriteLine("Please, enter a query and enjoy the result:\n");
            Main();
        }
    }
    static void ShowMeWhatYouGotGeneral()
    {

        string file1 = @"New Text Document.csv";
        string[] allLines = File.ReadAllLines(file1);

        if (sCommandDetails.Contains(LIMIT))
        {
            SetALimit();
        }
        else
        {
            ShowMeWhatYouGot();
        }
    }
    static void FindTheResults()
    {
        string file1 = @"New Text Document.csv";
        string[] allLines = File.ReadAllLines(file1);
        int iLastValue = sCommandDetails.Length - 1;

        string sStringToSearch = sCommandDetails[iLastValue];
        sStringToSearch = sStringToSearch.Replace("\"", "");

        string sBeautiful = "";
        Boolean first = true;
        int iItem = 0;
        string[] display;
        string sDisplayResult;
        string[] getColumnName = allLines[0].Split(',');

        sBeautiful = new String('*', 20 * allLines.Length - 1);
        Console.WriteLine(sBeautiful);

        for (int i = 0; i < getColumnName.Length; i++)
        {
            sDisplayResult = getColumnName[i];
            Console.Write(string.Format("| {0,-20}", sDisplayResult));
        }
        Console.WriteLine();
        Console.WriteLine(sBeautiful);
        first = true;
        Boolean newLineNeeded = false;

        foreach (var item in allLines)
        {
            if (first)
            {
                first = false;
                continue;
            }
            if (item.Contains(sStringToSearch))
            {
                iItem = item.Split(',').Length;
                display = item.Split(',');

                for (int i = 0; i < iItem; i++)
                {
                    sDisplayResult = display[i];
                    Console.Write(string.Format("| {0,-20}", sDisplayResult));
                    newLineNeeded = true;
                }
                if (newLineNeeded)
                {
                    Console.WriteLine();
                }
                newLineNeeded = false;
            }
        }
        Console.WriteLine(sBeautiful);
    }

    static void ShowMeWhatYouGot()
    {   

        int iItem = 0;
        string sDisplayResult = "";
        Boolean first = true;
        string sBeautiful = "";
        string[] display;
        string Translator2 = "";

        string file1 = @"New Text Document.csv";
        string[] allLines = File.ReadAllLines(file1);

        string sArrDisplay2 = String.Join(",", sCommandDetails, 1, sCommandDetails.Length - 1);
        string[] sArrDisplay = sArrDisplay2.Split(',');

        int iCountColumns = sCommandDetails.Length - 2;
        string[] getColumnName = allLines[0].Split(',');

        foreach (string item in allLines)
        {
            iItem = item.Split(',').Length;
            display = item.Split(',');
            for (int i = 0; i < iItem; i++)
            {
                if (sArrDisplay.Contains(display[i]))
                {
                    Translator2 = i + "," + Translator2;
                }
            }
        }
        
        //Removing the word SHOW from the Translator2
        Translator2 = Translator2.Remove(Translator2.Length - 1);

        foreach (string item in allLines)
        {
            sBeautiful = new String('*', 20 * Translator2.Length - 1);
            if (first)
            {
                Console.WriteLine(sBeautiful);
            }

            iItem = item.Split(',').Length;
            display = item.Split(',');

            for (int i = 0; i < iItem; i++)
            {
                if (Translator2.Contains(i.ToString()))
                {
                    sDisplayResult = display[i];
                    Console.Write(string.Format("| {0,-20}", sDisplayResult));
                }
            }

            Console.WriteLine();
            if (first)
            {
                Console.WriteLine(sBeautiful);
                first = false;
            }

        }
        Console.WriteLine(sBeautiful);
    }

    static void ShowHeader()
    {
        string file1 = @"New Text Document.csv";
        StreamReader sReader = new StreamReader(file1, Encoding.GetEncoding("Windows-1251"));
        Console.WriteLine(sReader.ReadLine());
    }

    static void SumValues()
    {
        string file1 = @"New Text Document.csv";
        string[] allLines = File.ReadAllLines(file1);

        int iLastValue = sCommandDetails.Length - 1;
        int iResult = -1;
        int iCounter = -1;

        string sColumnToWork = sCommandDetails[iLastValue];
        string[] getColumnName = allLines[0].Split(',');

        foreach (var item in getColumnName)
        {
            iCounter++;
            if (item == sColumnToWork)
            {
                iResult = iCounter;
            }
        }

        int iCountColumns = allLines[0].Split(',').Length;
        string sGetColumnThatWeAreTalkingAboutName = getColumnName[iResult];
        string sFirstLine = "";

        //Setting the header to look like: 0,0,0,0... etc, in order to be excluded from the sum:
        if (iCountColumns > 1)
        {
            for (int i = 0; i < iCountColumns - 1; i++)
            {
                sFirstLine = sFirstLine + "0,";
            }
            sFirstLine = sFirstLine + "0";
        }
        else
        {
            sFirstLine = "0";
        }

        allLines[0] = sFirstLine;

        IEnumerable strs = allLines;
        var columnQuery =
            from line in strs
            let elements = line.Split(',')
            select Convert.ToInt32(elements[iResult]);

        var results = columnQuery.ToList();
        double dSum = results.Sum();
        Console.WriteLine("\nThe sum of column [{0}] is  {1:0.##}!", sGetColumnThatWeAreTalkingAboutName, dSum);
    }

    static void SetALimit()
    {
        Boolean first = true;
        int iItem = 0;
        string sDisplayResult = "";
        string sBeautiful = "";
        string Translator2 = "";
        int z = -2;

        string file1 = @"New Text Document.csv";
        string[] allLines = File.ReadAllLines(file1);
        string sArrDisplay2 = String.Join(",", sCommandDetails, 1, sCommandDetails.Length - 1);
        string[] sArrDisplay = sArrDisplay2.Split(',');

        int Limit = int.Parse(sArrDisplay[sArrDisplay.Length - 1])-1;

        sArrDisplay = sArrDisplay.Reverse().Skip(2).Reverse().ToArray();
        int iCountColumns = sCommandDetails.Length - 2;

        string[] getColumnName = allLines[0].Split(',');
        string[] display;


        foreach (string item in allLines)
        {
            iItem = item.Split(',').Length;
            display = item.Split(',');
            for (int i = 0; i < iItem; i++)
            {
                if (sArrDisplay.Contains(display[i]))
                {
                    Translator2 = i + "," + Translator2;
                }
            }
        }

        //We remove the last comma from the string here:
        Translator2 = Translator2.Remove(Translator2.Length - 1);

        foreach (string item in allLines)
        {
            z++;
            if (z > Limit)
            {
                break;
            }

            sBeautiful = new String('*', 20 * Translator2.Length - 1);
            if (first)
            {
                Console.WriteLine(sBeautiful);
            }

            iItem = item.Split(',').Length;
            display = item.Split(',');

            for (int i = 0; i < iItem; i++)
            {
                if (Translator2.Contains(i.ToString()))
                {
                    sDisplayResult = display[i];
                    Console.Write(string.Format("| {0,-20}", sDisplayResult));
                }
            }
            Console.WriteLine();
            if (first)
            {
                Console.WriteLine(sBeautiful);
                first = false;
            }
        }
        Console.WriteLine(sBeautiful);
    }
}

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using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.IO;

using System.Text.RegularExpressions;

class CSV_query_language

{

public static string[] sCommandActivate;

public static string[] sCommandDetails;

public const string SHOW = "show";

public const string SUM = "sum";

public const string FIND = "find";

public const string SELECT = "select";

public const string LIMIT = "limit";

static void Main()

{

try

{

string sCommand = Console.ReadLine();

sCommandActivate = sCommand.Split('>');

sCommandDetails = sCommandActivate[1].Split(' ');

if (sCommandDetails.Contains(SHOW))

{

ShowHeader();

}

if (sCommandDetails.Contains(SUM))

{

SumValues();

}

if (sCommandDetails.Contains(FIND))

{

FindTheResults();

}

if (sCommandDetails.Contains(SELECT))

{

ShowMeWhatYouGotGeneral();

}

Console.WriteLine("\nThank you for using the custom query language!\nPress Y for a new query.");

string sNewQuery = Console.ReadLine();

if (sNewQuery == "Y" || sNewQuery == "y")

{

Main();

}

catch (Exception ex)

{

Console.WriteLine(ex.Message);

Console.WriteLine("\nAn error has occurred. Try again!");

Console.WriteLine("Possible queries:\n");

Console.WriteLine("query> show");

Console.WriteLine("query> sum id");

Console.WriteLine("query> select id, name, age limit 5");

Console.WriteLine("query> select id, experience");

Console.WriteLine("query> find \"-\"");

Console.WriteLine("Please, enter a query and enjoy the result:\n");

Main();

}

static void ShowMeWhatYouGotGeneral()

{

string file1 = @"New Text Document.csv";

string[] allLines = File.ReadAllLines(file1);

if (sCommandDetails.Contains(LIMIT))

{

SetALimit();

}

else

{

ShowMeWhatYouGot();

}

static void FindTheResults()

{

string file1 = @"New Text Document.csv";

string[] allLines = File.ReadAllLines(file1);

int iLastValue = sCommandDetails.Length - 1;

string sStringToSearch = sCommandDetails[iLastValue];

sStringToSearch = sStringToSearch.Replace("\"", "");

string sBeautiful = "";

Boolean first = true;

int iItem = 0;

string[] display;

string sDisplayResult;

string[] getColumnName = allLines[0].Split(',');

sBeautiful = new String('*', 20 * allLines.Length - 1);

Console.WriteLine(sBeautiful);

for (int i = 0; i < getColumnName.Length; i++)

{

sDisplayResult = getColumnName[i];

Console.Write(string.Format("| {0,-20}", sDisplayResult));

}

Console.WriteLine();

Console.WriteLine(sBeautiful);

first = true;

Boolean newLineNeeded = false;

foreach (var item in allLines)

{

if (first)

{

first = false;

continue;

}

if (item.Contains(sStringToSearch))

{

iItem = item.Split(',').Length;

display = item.Split(',');

for (int i = 0; i < iItem; i++)

{

sDisplayResult = display[i];

Console.Write(string.Format("| {0,-20}", sDisplayResult));

newLineNeeded = true;

}

if (newLineNeeded)

{

Console.WriteLine();

}

newLineNeeded = false;

}

Console.WriteLine(sBeautiful);

}

static void ShowMeWhatYouGot()

{

int iItem = 0;

string sDisplayResult = "";

Boolean first = true;

string sBeautiful = "";

string[] display;

string Translator2 = "";

string file1 = @"New Text Document.csv";

string[] allLines = File.ReadAllLines(file1);

string sArrDisplay2 = String.Join(",", sCommandDetails, 1, sCommandDetails.Length - 1);

string[] sArrDisplay = sArrDisplay2.Split(',');

int iCountColumns = sCommandDetails.Length - 2;

string[] getColumnName = allLines[0].Split(',');

foreach (string item in allLines)

{

iItem = item.Split(',').Length;

display = item.Split(',');

for (int i = 0; i < iItem; i++)

{

if (sArrDisplay.Contains(display[i]))

{

Translator2 = i + "," + Translator2;

}

//Removing the word SHOW from the Translator2

Translator2 = Translator2.Remove(Translator2.Length - 1);

foreach (string item in allLines)

{

sBeautiful = new String('*', 20 * Translator2.Length - 1);

if (first)

{

Console.WriteLine(sBeautiful);

}

iItem = item.Split(',').Length;

display = item.Split(',');

for (int i = 0; i < iItem; i++)

{

if (Translator2.Contains(i.ToString()))

{

sDisplayResult = display[i];

Console.Write(string.Format("| {0,-20}", sDisplayResult));

}

Console.WriteLine();

if (first)

{

Console.WriteLine(sBeautiful);

first = false;

}

Console.WriteLine(sBeautiful);

}

static void ShowHeader()

{

string file1 = @"New Text Document.csv";

StreamReader sReader = new StreamReader(file1, Encoding.GetEncoding("Windows-1251"));

Console.WriteLine(sReader.ReadLine());

}

static void SumValues()

{

string file1 = @"New Text Document.csv";

string[] allLines = File.ReadAllLines(file1);

int iLastValue = sCommandDetails.Length - 1;

int iResult = -1;

int iCounter = -1;

string sColumnToWork = sCommandDetails[iLastValue];

string[] getColumnName = allLines[0].Split(',');

foreach (var item in getColumnName)

{

iCounter++;

if (item == sColumnToWork)

{

iResult = iCounter;

}

int iCountColumns = allLines[0].Split(',').Length;

string sGetColumnThatWeAreTalkingAboutName = getColumnName[iResult];

string sFirstLine = "";

//Setting the header to look like: 0,0,0,0... etc, in order to be excluded from the sum:

if (iCountColumns > 1)

{

for (int i = 0; i < iCountColumns - 1; i++)

{

sFirstLine = sFirstLine + "0,";

}

sFirstLine = sFirstLine + "0";

}

else

{

sFirstLine = "0";

}

allLines[0] = sFirstLine;

IEnumerable strs = allLines;

var columnQuery =

from line in strs

let elements = line.Split(',')

select Convert.ToInt32(elements[iResult]);

var results = columnQuery.ToList();

double dSum = results.Sum();

Console.WriteLine("\nThe sum of column [{0}] is {1:0.##}!", sGetColumnThatWeAreTalkingAboutName, dSum);

}

static void SetALimit()

{

Boolean first = true;

int iItem = 0;

string sDisplayResult = "";

string sBeautiful = "";

string Translator2 = "";

int z = -2;

string file1 = @"New Text Document.csv";

string[] allLines = File.ReadAllLines(file1);

string sArrDisplay2 = String.Join(",", sCommandDetails, 1, sCommandDetails.Length - 1);

string[] sArrDisplay = sArrDisplay2.Split(',');

int Limit = int.Parse(sArrDisplay[sArrDisplay.Length - 1])-1;

sArrDisplay = sArrDisplay.Reverse().Skip(2).Reverse().ToArray();

int iCountColumns = sCommandDetails.Length - 2;

string[] getColumnName = allLines[0].Split(',');

string[] display;

foreach (string item in allLines)

{

iItem = item.Split(',').Length;

display = item.Split(',');

for (int i = 0; i < iItem; i++)

{

if (sArrDisplay.Contains(display[i]))

{

Translator2 = i + "," + Translator2;

}

//We remove the last comma from the string here:

Translator2 = Translator2.Remove(Translator2.Length - 1);

foreach (string item in allLines)

{

z++;

if (z > Limit)

{

break;

}

sBeautiful = new String('*', 20 * Translator2.Length - 1);

if (first)

{

Console.WriteLine(sBeautiful);

}

iItem = item.Split(',').Length;

display = item.Split(',');

for (int i = 0; i < iItem; i++)

{

if (Translator2.Contains(i.ToString()))

{

sDisplayResult = display[i];

Console.Write(string.Format("| {0,-20}", sDisplayResult));

}

Console.WriteLine();

if (first)

{

Console.WriteLine(sBeautiful);

first = false;

}

Console.WriteLine(sBeautiful);

}

Enjoy it.

Tagged with: C#, HackBulgaria, query language, query with C#, query with csv files

C# – Make your own query language

Problem 3 – A query language over a CSV file

Features

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