Question

I am trying to implement an API with the following signature:

public static List<string> SearchDatabase(
    string column,
    string value);

The implementation of the API needs to construct an SQL SELECT query with a WHERE clause that uses a column name specified in the column parameter.

The query:

string query =
    string.Format(
        "SELECT Name, @Column " +
        "FROM Db1 " +
        "INNER JOIN Db2 ON Db1.Id = Db2.Id " +
        "WHERE @Column = @Value");

The SQL command and parameters:

SqlCommand selectCmd =
    new SqlCommand(
        query,
        connection);
selectCmd.CommandTimeout = SqlCommandTimeout;
selectCmd.Parameters.AddRange(
    new SqlParameter[]
{
    new SqlParameter("@Column", column),
    new SqlParameter("@Value", value)
});

And I execute it like this:

SqlDataReader sqlDataReader = selectCmd.ExecuteReader();
while (sqlDataReader.Read())
{
    // ...
}

The problem is that sqlDataReader doesn’t return any rows, so I don’t go into the while loop above.

However, if I change the last line of the query above from:

"WHERE @Column = @Value");

to

"WHERE Vendor = @Value");

(i.e. hardcode the column name to ‘Vendor’) then it works.

My understanding from research I have done is that it’s not possible to pass column names as parameters, but only values we are querying on. But, it does appear to let me use the @Column parameter in the SELECT clause, just not the WHERE clause.

I don’t want to resort to dynamic SQL because of the issues with SQL injection. Is there another way around this?

Answer 1

Unfortunately table names, column names cannot be parametrized. Because you know the structure of the table you could have a whitelist of possible column names in this parameter and then use string concatenation for it to avoid SQL injection:

"WHERE " + Sanitize(column) + " = @Value");