Database

IDbConnection connection = new OleDbConnection(str);

IDbConnection connection = new SqlConnection(str);

IDbCommand atrCommand = connection.CreateCommand();

private IDbConnection conn = null;
private Type connType = null;

SqlConnection connection = new SqlConnection(str);

conn = (IDbConnection)connection;

connType = connection.GetType();

if (connType == typeof(SqlConnection))
    SqlConnection sqlConn = (SqlConnection)conn;
else if (...)
{}

Without nipples, breasts would be pointless.

-- Join in WHERE clause.
USE pubs
SELECT t.title_id, t.title, s.qty
FROM titles AS t, sales AS s
WHERE t.title_id *= s.title_id

-- Join in FROM clause.
USE pubs
SELECT t.title_id, t.title, s.qty
FROM titles AS t LEFT OUTER JOIN sales AS s
   ON t.title_id = s.title_id

-- Join and search condition in WHERE clause.
USE pubs
SELECT t.title_id, t.title, s.qty
FROM titles AS t, sales AS s
WHERE t.title_id *= s.title_id
   AND s.stor_id = '7066'

USE pubs
SELECT t.title_id, t.title, s.qty
FROM titles AS t LEFT OUTER JOIN sales AS s
   ON t.title_id = s.title_id
WHERE s.stor_id = '7066'

USE pubs
SELECT t.title_id, t.title, s.qty
FROM titles AS t LEFT OUTER JOIN sales AS s
   ON t.title_id = s.title_id 
   AND s.stor_id = '7066'