使用where子句计算sql数据的行数答案

【问题标题】：Counting rows of sql data using where clause使用where子句计算sql数据的行数
【发布时间】：2019-10-06 04:39:45
【问题描述】：

quiz_record 表：

我需要计数所有具有marks 小于 Student_Id['4'] 的marks 的行。

也，如果其他人的标记与Student_Id['4']的标记相差相同，那么也计算所有time gap (Quiz_End - Quiz_Start)大于的人Student_Id['4']中的time gap (Quiz_End - Quiz_Start)。

预期结果：2

为此我尝试过：

$time_taken = strtotime($fetch_quiz_record['Quiz_End']) - strtotime($fetch_quiz_record['Quiz_Start']);

$count_less_played = $user->runQuery("SELECT COUNT(Id) AS Id FROM quiz_record WHERE Quiz_Id=:quiz_id AND Marks<=:marks AND (Quiz_End - Quiz_Start) >:time_diff");

$count_less_played->bindparam(":quiz_id",$fetch_quiz_record['Quiz_Id']);
$count_less_played->bindparam(":marks",$fetch_quiz_record['Marks']);
$count_less_played->bindparam(":time_diff",$time_taken);

$count_less_played->execute();

$count_less_played_cnt = $count_less_played->fetch(PDO::FETCH_ASSOC);

echo $count_less_played_no= $count_less_played_cnt['Id'];

输出：4

【问题讨论】：

标签： php mysql mysqli pdo count

【解决方案1】：

试试这个（在 cmets 中有解释）：

$time_taken = strtotime($fetch_quiz_record['Quiz_End']) - strtotime($fetch_quiz_record['Quiz_Start']);

/////--Counting Rows which have less than marks--/////

$count_less_marks = $user->runQuery("SELECT COUNT(Id) AS Id FROM quiz_record WHERE Quiz_Id=:quiz_id AND Marks<:marks");

$count_less_marks->bindparam(":quiz_id",$fetch_quiz_record['Quiz_Id']);
$count_less_marks->bindparam(":marks",$fetch_quiz_record['Marks']);

$count_less_marks->execute();

$count_less_marks_cnt = $count_less_marks->fetch(PDO::FETCH_ASSOC);

$count_less_marks_no= $count_less_marks_cnt['Id'];

/////--Counting Rows which have equal marks and time difference more--/////

$count_more_time = $user->runQuery("SELECT COUNT(Id) AS Id FROM quiz_record WHERE Quiz_Id=:quiz_id AND Marks=:marks AND TIMESTAMPDIFF(SECOND, Quiz_Start, Quiz_End) > :time_diff");

$count_more_time->bindparam(":quiz_id",$fetch_quiz_record['Quiz_Id']);
$count_more_time->bindparam(":marks",$fetch_quiz_record['Marks']);
$count_more_time->bindparam(":time_diff",$time_taken);

$count_more_time->execute();

$count_more_time_cnt = $count_more_time->fetch(PDO::FETCH_ASSOC);

$count_more_time_no= $count_more_time_cnt['Id'];

/////--Add both counts, to get required results--/////

$count_less_played = $count_less_marks_no + $count_more_time_no;

echo $count_less_played;

【讨论】：

【解决方案2】：

首先，你能指定 $user 和 $fetch_quiz_record 是什么吗？如果没有这些信息，我会首先选择参考，在您的情况下是 quiz_record，Student_Id 为 4。

$statement = $conn->prepare("
  SELECT 
    Quiz_Start,
    Quiz_End,
    Marks
  FROM quiz_record
  WHERE Student_Id = :student_id  
");

// in your case $student_id would be 4
$res = $statement->execute([':student_id' => $student_id]);
$selected_quiz = $res->fetch(PDO::FETCH_ASSOC);

$count_statement = $conn->prepare("
  SELECT 
    COUNT(*) as quiz_count
  FROM quiz_record
  WHERE 
    Marks < :mark_limit OR
    (Marks = :mark_limit AND TIMESTAMPDIFF(SECOND, Quiz_Start, Quiz_End > :seconds_diff))
");

// depending on the datatype of Quiz_Start and Quiz_End
$quiz_start = \DateTimeImmutable::createFromFormat("Y-m-d H:i:s", $selected_quiz['Quiz_Start']);
$quiz_end = \DateTimeImmutable::createFromFormat("Y-m-d H:i:s", $selected_quiz['Quiz_End']);
$diff_in_seconds =  abs($quiz_end->getTimestamp() - $quiz_start->getTimestamp());

$count_res = $count_statement->execute([
  ':mark_limit' => $selected_quiz['Marks'], 
  ':seconds_diff' => $diff_in_seconds
]);

$fetched = $count_res->fetch(PDO::FETCH_ASSOC);
// $count should be the count
$count = $fetched['quiz_count'];

请注意，此代码应该在您的数据层中。如果提供更多详细信息，我可以详细说明。

【讨论】：