Question

I have nine strings which either are a SQL query or just empty (“”), depending on the state of several checkboxes. I need to combine them in another string like

string OP = "AND";
string query = "select * from table where " + string1 + OP + string2 + OP + string3 + OP + ... + " order by ID;"

The problem is, in between of the strings, I need to have an AND or an OR. But if any of the strings are empty, it gives me a SQL error. SQL doesn’t understand something like

select * from table where AND a = "adsf" AND AND AND z = "fghj" AND order by ID;

it has to look like this:

select * from table where a = "adsf" AND z = "fghj" order by ID;

Answer 1

You can put the strings in an array, remove the empty strings, and combine them using Join:

string[] conditions = new string[] {
  string1,
  string2,
  string3,
  string4
};

string op = " and ";
string query =
  "select * from table where " +
  String.Join(op, conditions.Where(c => c.Length > 0)) +
  "select * from table where ";

And for framework 3.5 change to:

  String.Join(op, conditions.Where(c => c.Length > 0).ToArray()) +