Using Regex to extract table names from a file containing SQL queries

Question

I\'ve a text file containing large number of queries. I want to get all the distinct tables used in the entire file in all the queries. The table name can come after a \'fro

Answer 1

can try this but it doesnt work for all the types of query,

  public void Main()
    {
        // TODO: Add your code here

        string Line = string.Empty;

        using (StreamReader sr = new StreamReader(@"D:\ssis\queryfile.txt"))//reading the filename
        {

            var text = string.Empty;

            do
            {
                //     MessageBox.Show(Line);
                text = Line = sr.ReadToEnd();// storing it in a variable by reading till end

                MessageBox.Show(Line);



            } while ((Line = sr.ReadLine()) != null);



            var text1 = text.Replace("[", string.Empty).Replace("]", string.Empty);//replacing brackets with empty space

            MessageBox.Show(text1);



            Regex r = new Regex(@"(?<=from|join)\s+(?<table>\S+)", RegexOptions.IgnoreCase | RegexOptions.Compiled);//regex for extracting the tablename after from and join

            Match m = r.Match(text1);//creating match object

            MessageBox.Show(m.Groups[1].Value);

            var v = string.Empty;



            while (m.Success)
            {

                v = m.Groups[0].Value;

                m = m.NextMatch();


                StreamWriter wr = new StreamWriter(@"D:\ssis\writefile.txt", true);// writing the match to the file

                var text2 = v.Replace(".", " ,"); // replace the . with , seperated values


                wr.WriteLine(text2);

                sr.Close();
                wr.Close();

            }
        }
    }

Answer 2

It depends on structure of your file. Try to use this:

(?<=from|join)(\s+\w+\b)

Also turn on options Multiline if your not split your file in array or smth else with singleline string members. Also try to turn on IgnorCase option.

Answer 3

I'd use:

r = new Regex("(from|join)\s+(?<table>\S+)", RegexOptions.IgnoreCase);

once you have the Match object "m", you'll have the table name with

m.Groups["table"].Value

example:

string line = @"select * from tb_name join tb_name2 ON a=b WHERE x=y";
Regex r = new Regex(@"(from|join)\s+(?<table>\S+)",
         RegexOptions.IgnoreCase|RegexOptions.Compiled);

Match m = r.Match(line);
while (m.Success) {
   Console.WriteLine (m.Groups["table"].Value);
   m = m.NextMatch();
}

it will print: tb_table tb_table2

Answer 4

(from|join)\s(\w+)

Answer 5

Something like this maybe:

/(from|join)\s+(\w*\.)*(?<tablename>\w+)/

It won't match escaped table names though, and you need to make the regex evaluation case-insensitive.