can we execute plsql commands in sql plus code example

Example 1: How can I prevent SQL injection in PHP?

//Connect
$unsafe_variable = $_POST["user-input"];
$safe_variable = mysql_real_escape_string($unsafe_variable);

mysql_query("INSERT INTO table (column) VALUES ('" . $safe_variable . "')");
//Disconnect

Example 2: sql run multiple updates in one query

UPDATE table_name
SET   field_name = 
      case  field_name2 
      when 'value' then 'change_to'
      when 'value2' then 'change_to2'
end