Database and SQL C#

Ignoring your code example it seems to me there are a couple of things going on here.

1. You want to built a list of star'd words entered into textbox1
2. You want to output the star'd word list to textbox2
3. Store a frequency list of the stared words

Points 1 and 2 can be done without interaction with the database. Perhaps using a regex to pattern match words being with *.

Point 3 should be a case executing a sql statement that either inserts new words with a count of 1 or updates the count of known words by 1.

EDIT following comments

Point 1 - build a list of words

var matches = new System.Text.RegularExpressions.Regex("\\*[^ \t]+").Matches(textbox1);

foreach (Match match in matches)
    Console.WriteLine(match.Value);

Point 3 - store words for frequency list

//using statement to ensure connection is cleaned up correctly
using (SqlConnection connection = new SqlConnection(@"Server=.\SQLEXPRESS;Database=StoreList;Integrated Security=sspi"))
{
    connection.Open();

    foreach (Match match in matches)
    {
        var command = new SqlCommand("UpdateWordFrequency", connection);

        command.CommandType = System.Data.CommandType.StoredProcedure;
        command.Parameters.Add(new SqlParameter("@word", match.Value));

        command.ExecuteNonQuery();
    }
}

Where the procedure looks like this

create procedure UpdateWordFrequency
    @word varchar(50)
as
if not exists (select 1 from WordList where word = @word)
    insert into WordList (word, frequency) values (@word, 0)

update WordList set frequency = frequency + 1 where word = @word

And the WordList table has 2 fields word (varchar) and frequency (int)

Point 2 - output star'd words

Well this should now be a case of selecting from the WordList table

It might be better to use a stored procedure for this.

By using a stored procedure you can do something like this:

create procedure Insert_StoreList
@Word nvarchar(50)
AS

insert StoreList (
item )
values (
@Word )

SELECT item FROM StoreList WHERE item LIKE '*%'

Then you can use the following in C#

SqlCommand com = new SqlCommand("Insert_StoreList", con);
com.CommandType = CommandType.StoredProcedure;
com.Parameters.Add(new SqlParameter("@Word", Textbox1.Text));
SqlDataReader sdr = com.ExecuteReader();

Edit - If you won't like to use stored procedures you can do this with 2 lines of SQL too, The first one would be an ExecuteNonQuery to get the value into the Table, and the second one would be to select all the words from the table.

The first sql would be:

String queryStr = "insert StoreList (item) values (" + Textbox1.Text + ")"; 

The second sql would be:

String queryStr = "SELECT item FROM StoreList WHERE item LIKE '*%'";