c# - How can I use the Like Operator with a Parameter in a SQLite query?

Question

I can get the result I expect by entering this in LINQPad:

SELECT * FROM WorkTable WHERE WTName LIKE "DSD__20090410014953000%"

(it shows me the record which has a WTName value of DSD__20090410014953000.xml")

But trying to do this programmatically is proving trying. I tried:

const string qry = "SELECT SiteNum FROM WorkTable WHERE WTName LIKE @wtName%";
using (SQLiteConnection con = new SQLiteConnection(HHSUtils.GetDBConnection()))
{
    con.Open();
    SQLiteCommand cmd = new SQLiteCommand(qry, con);
    cmd.Parameters.Add(new SQLiteParameter("wtName", tableName));
    siteNum = Convert.ToInt32(cmd.ExecuteScalar());
}

...but it causes the app to crash, and my log file tells me why:

Message: From application-wide exception handler: System.Data.SQLite.SQLiteException: SQL logic error or missing database
near "%": syntax error

So maybe it thinks the query parameter is named "wtName%" instead of "wtName"; but separating the parameter and the "whatever" opertor ("%") with a space doesn't work, either.

I could go retro/kludgy by just embedding the query parameter into the string like so:

const string qry = String.Format("SELECT SiteNum FROM WorkTable WHERE WTName LIKE {0}%", tableName);

...and doing without the query parameter altogether, but I'm afraid if I did that Troy Hunt would show up at my house and flail me with a bedrail while railing about SQL Injection.

How can I get my data and simultaneously write safe code?

Answer 1

The wildcard % should be added to the parameter value, not to the parameter name

const string qry = "SELECT SiteNum FROM WorkTable WHERE WTName LIKE @wtName";
using (SQLiteConnection con = new SQLiteConnection(HHSUtils.GetDBConnection()))
{
    con.Open();
    SQLiteCommand cmd = new SQLiteCommand(qry, con);
    cmd.Parameters.Add(new SQLiteParameter("@wtName", tableName + "%"));
    siteNum = Convert.ToInt32(cmd.ExecuteScalar());
}

And, I am not sure if it matters here, but, usually, I insert the parameter name with the exact name used in the placeholder ( @wtName )