MySQL连接两个表的where子句

Question

So I'm listing some activities based on a form where the user select the country, date, etc.. There's two tables, the main one "actividades" is where I have the name, price, number of participants, etc and then I have "tarifas" where I put special rules for activities, for example if on a specific day that activity is available or not. there could be a rule or not, if there's not any rule, I want to list that activity, if there's a rule, I only want to list it if that day is availabe which is what tarifas.fechado = 0 is supposed to do.

Everything else is working, can someone help me sort this out?

if (!$sql = $db->sql_query("SELECT actividades.dias, actividades.id_pais, actividades.id_regiao, actividades.nome, actividades.id_empresa, actividades.id, actividades.dias, actividades.preco, actividades.id_subcategoria, actividades.hora 
                            FROM actividades 
                            LEFT JOIN tarifas ON actividades.id = tarifas.id_actividade 
                                              AND tarifas.dia = '$dia' 
                                              AND tarifas.fechado = 0 
                            WHERE pais = '$pais' 
                            AND actividades.dias LIKE '%$diaExtenso%' 
                            ORDER BY actividades.id ASC 
                            LIMIT $pageLimit, $porpagina")) 
       {message_die("DS", TRUE); }

Answer 1

I think some of your join conditions need to be in the WHERE clause instead. I'm not clear on how tarifas.dia fits into the picture, but this query will return all actividades rows that have no related tarifas row, plus all those that do have a tarifas row for which tarifas.dia has the specified value and tarifas.fechado is zero. (I have formatted it for readability):

SELECT
  actividades.dias,
  actividades.id_pais,
  actividades.id_regiao,
  actividades.nome,
  actividades.id_empresa,
  actividades.id,
  actividades.dias,
  actividades.preco,
  actividades.id_subcategoria,
  actividades.hora
FROM
  actividades
  LEFT JOIN tarifas
    ON actividades.id = tarifas.id_actividade
WHERE
  pais = '$pais'
  AND actividades.dias LIKE '%$diaExtenso%'
  AND (tarifas.id_actividade IS NULL
    OR (tarifas.dia = '$dia' AND tarifas.fechado = 0))
ORDER BY actividades.id ASC
LIMIT $pageLimit, $porpagina

It is possible that you want to move the condition on tarifas.dia back into the join predicate. Doing so would cause tarifas rows to be ignored unless they have the specified dia value.