Explanation:
The method is this:
public function join($table, $cond, $type = '')
{
if ($type != '')
{
$type = strtoupper(trim($type));
if ( ! in_array($type, array('LEFT', 'RIGHT', 'OUTER', 'INNER', 'LEFT OUTER', 'RIGHT OUTER')))
{
$type = '';
}
else
{
$type .= ' ';
}
}
// Extract any aliases that might exist. We use this information
// in the _protect_identifiers to know whether to add a table prefix
$this->_track_aliases($table);
// Strip apart the condition and protect the identifiers
if (preg_match('/([\w\.]+)([\W\s]+)(.+)/', $cond, $match))
{
$match[1] = $this->_protect_identifiers($match[1]);
$match[3] = $this->_protect_identifiers($match[3]);
$cond = $match[1].$match[2].$match[3];
}
// Assemble the JOIN statement
$join = $type.'JOIN '.$this->_protect_identifiers($table, TRUE, NULL, FALSE).' ON '.$cond;
$this->ar_join[] = $join;
if ($this->ar_caching === TRUE)
{
$this->ar_cache_join[] = $join;
$this->ar_cache_exists[] = 'join';
}
return $this;
}
Then, $table
is the name of the table that relates the $cond
is the condition and $type
that can be some of these 'LEFT', 'RIGHT', 'OUTER', 'INNER', 'LEFT OUTER', 'RIGHT OUTER'
Example
$this->db->from('cliente')
->join('telefone', 'cliente.id = telefone.clienteid', 'left')
->get()
->result();
This is the format it is limited to putting a SQL in there because by automatic it puts an escape ( '), this SQL being generated by it:
SELECT * FROM ('cliente') LEFT JOIN 'telefone' ON 'cliente'.'id' = 'telefone'.'clienteid'
Solution:
$query = $this->db->query("SELECT count(rl.id) as total, rl.dt_validate FROM respostas r JOIN respostas_log rl ON rl.id = (select max(rl2.id) from respostas_log rl2 where rl2.respostas_id = r.id) GROUP BY rl.dt_validate");
Actually you already have the solution and when doing a complex SQL is the best way to execute SQL statements in CodeIgniter.