如何从一列 select 最大值并使用选定的最大值更新另一列

Question

$query6 = "SELECT MAX(subject_total) AS max FROM results1 WHERE subjects = '{$result_subject}' AND class = '{$student_class}' AND term = '{$result_term}' AND session = '{$result_session}'";

$run_query6 = mysqli_query($connection, $query6);

while($run_query6 = mysqli_fetch_assoc($run_query6)) {
    $max = $run_query6['max'];
} 
$sql1 = "UPDATE results1 SET max = ".($max)." WHERE max = ".$max;
$run_query6 = mysqli_query($connection, $sql1); } 

When I run the above code, $sql1 query doesn't update max column. Please help me fix this. I need for the query to update max column with same max value. Eg if 70 is max score in English, it will update all English rows with 70. But its not updating max column.

Answer 1

You seem to want a window function:

select t.*,
       max(subject_total) over (partition by subject) as subject_max
from t;

Answer 2

You just need one query to do the whole job:

UPDATE 
    subjects 
join 
    (SELECT subject, max(subject_total) as subject_max from subjects group by subject) m        
    on (subjects.subject = m.subject) 
set 
    subjects.subject_max = m.subject_max;

The subquery selects the maximum value for each subject by using the GROUP BY clause.

The JOIN links the subquery to the main table on the subject column so that the SET can populate the values.

Output:

# id, user,  subject, subject_total, subject_max
1,    sam,   English, 50,            51
2,    abi,   English, 51,            51
3,    sam,   agric,   52,            53
4,    abi,   agric,   53,            53
5,    sam,   ICT,     54,            55
6,    abi,   ICT,     55,            55
7,    sam,   French,  56,            58
8,    abi,   French,  57,            58
9,    candy, French,  58,            58

Be careful with max as a column name - I think it's a MySQL reserved word. My example uses subject_max instead