Read rows in from database and assign the rows values to a string variable in Postgresql and C#

Question

I have a table in my database consisting of one column which is NewLanguage(varchar).I insert new languages to the table and i want to select the rows of the table and assign them to a string variable splitted by ','. I try to select the languages as in the code.

public string  SelectLanguagesFromDatabase()
    {

        NpgsqlCommand COM = new NpgsqlCommand(null,dbConnection);
        COM.CommandText = "select * from \"Languages\"";


    }

How can I select roes from database and assign them to string variable?

In an example

if Languages Column is

  NewLanguage

 C
 c++
 java

I want to have a a string as "C,c++,java". How can I do that ? Thanks.

Ilesh Patel · Accepted Answer · 2014-07-23 07:46:34Z

2

You can use string_agg to concatenate all values from particular column in comma separated text like below:

SELECT string_agg (NewLanguage,',') FROM "Languages"

answered Jul 23, 2014 at 7:46

Ilesh Patel

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2 Comments

user3864949 Over a year ago

@Ilesh Patel I updated my method then a i have another question which is what must be this method's return value?

Ilesh Patel Over a year ago

if you store result into variable name like INTO var than it should be TEXT

Community · Accepted Answer · 2017-05-23 10:25:04Z

0

Adapted from the user manual and using Ilesh Patel's query:

using System;
using System.Data;
using Npgsql;

public static class NpgsqlUserManual
{
  public static void Main(String[] args)
  {
    NpgsqlConnection conn = new NpgsqlConnection("Server=127.0.0.1;Port=5432;User Id=joe;Password=secret;Database=joedata;");
    conn.Open();

    NpgsqlCommand command = new NpgsqlCommand("SELECT string_agg(NewLanguage,',') FROM Languages", conn);
    String results;

    try
    {
      results = (String)command.ExecuteScalar();
      Console.WriteLine("{0}", results);
    }


    finally
    {
      conn.Close();
    }
  }
}

edited May 23, 2017 at 10:25

CommunityBot

11 silver badge

answered Jul 23, 2014 at 8:08

mhawke

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