sql or語法

1.mysql中or語法的使用，在mysql語法中or使用註意點。 項目遇到坑，遍歷發放獎勵數據查詢錯誤！！！

  $sql = 'SELECT 
                * 
            FROM 
                `vvt_spread_doubleegg_exchange_award` AS p
            WHERE
                p.`act_type` = 4 or p.`act_type` = 5
            AND
                p.`user_id` = ' .$user_id
            ;

sql中的or語法一般用於多個條件的查詢，上面的語法查詢的相當於：兩個sql查詢出來的數據集合。

  $sql = 'SELECT *  FROM  `vvt_spread_doubleegg_exchange_award` AS p WHERE  p.`act_type` = 4;
  $sql = 'SELECT * FROM `vvt_spread_doubleegg_exchange_award` AS p WHERE  p.`act_type` = 5 AND p.`user_id` = ' .$user_id;

2.  要想查詢act_type = 4  and user_id = 11123 或者等於 p.`act_type` = 5 and user_id = 11123的數據集合 or兩邊的條件一定要加（）。

  $sql = 'SELECT 
                * 
            FROM 
                `vvt_spread_doubleegg_exchange_award` AS p
            WHERE
                （p.`act_type` = 4 or p.`act_type` = 5）
            AND
                p.`user_id` = ' .$user_id
            ;