php - 哪一个更好？情况何时或是否有其他情况？

Question

我的情况是这样的:

情况是这样的:

public function get_opportunity($customer_id, $group_id, $action)
{
    $sql = "SELECT COUNT(transaction_id) AS total_transaction 
            FROM `transaction` 
            WHERE 
                CASE 
                    WHEN '$action' = 'view_all' THEN transaction_id IS NOT NULL
                    WHEN '$action' = 'view_group' THEN group_id IN($group_id) 
                    ELSE transaction_created_by = ? 
                END 
            ";

    $result = $this->db->query($sql, array($customer_id))->result_array();

    return ($result[0]['total_transaction']) ? $result[0]['total_transaction'] : 0;
}

如果 else 是这样的:

public function get_opportunity($customer_id, $group_id, $action)
{
    if($action == "view_all")
        $condition = " transaction_id IS NOT NULL";
    else if($action == 'view_group')
        $condition = " group_id IN($group_id)";
    else
        $condition = " customer_id = ?";

    $sql = "SELECT COUNT(transaction_id) AS total_transaction 
            FROM `transaction` 
            WHERE $condition";

    $result = $this->db->query($sql, array($customer_id))->result_array();

    return ($result[0]['total_transaction']) ? $result[0]['total_transaction'] : 0;
}

我试过了。以上作品的所有类型。但我想问一下，哪个更好？

Answer 1

这不可能，第一个代码不应该工作!在 SQL 中，CASE 是一个表达式，而不是语句。您不能在 THEN 部分添加条件，只能添加一个值。 MySQL 将 bool 表达式计算为 1\0 ，所以你的情况基本上是这样的:

WHERE CASE... THEN (Cond) -- equals to 1/0 
              THEN (Cond) -- equals to 1/0
              ELSE (Cond) -- -- equals to 1/0 

大多数 RDBMS 都会抛出错误。

你可以这样格式化:

SELECT COUNT(transaction_id) AS total_transaction 
            FROM `transaction` 
            WHERE ('$action' = 'view_all' AND transaction_id IS NOT NULL) OR 
                  ('$action' = 'view_group' THEN group_id IN($group_id)) OR
                  transaction_created_by = ?       

只要你没有性能问题，就不要考虑这些东西，这只会浪费你的时间。选择一个对您来说更容易维护的。