build a string of ints for SQL WHERE IN [closed]

First you query will fail in SQL Server, it should be written like:

SELECT * FROM tableA WHERE id IN (WhereClause)

What I would suggest is to use the following method to generate your whereclause:

public static string ToIntCSV(this IEnumerable<int> ints)
{
  if (ints == null) throw new ArgumentNullException("ints");
  string result = string.Empty;
  foreach(int i in ints)
  {
    if (string.IsNullOrEmpty) result = i.ToString();
    else result += string.Format(",{0}",i);
  }
  return result;
}

You could potentially use a StringBuilder if you expect large quantities of integers. Alternatively you could use the LINQ Aggregate() extension too.

public static string ToIntCSV(this IEnumerable<int> ints)
{
  if (ints == null) throw new ArgumentNullException("ints");
  return ints.Aggregate((csvSoFar, next) => string.Format("{0},{1}",csvSoFar,next);
}

This also ensures you actually have a list of integers for your where clause.

Finally to build your query, you should get into the habit of using string.Format():

  public void GetQuery(IEnumerable<int> ints)
  {
     try
     {
     var query = string.Format("SELECT * FROM [tableA] WHERE [ID] IN ({0})",ints.toIntCSV());
      //perform sql command
     }
     catch (ArgumentNullException)
     {
        MessageBox.Show("Invalid input");
     }
  }

Note, unfortunately you cannot use a parameterized query in this instance, but be sure to use them elsewhere.