Question

I have a database with this kind of a table, has more than 10 million rows.

ID  colA    colB    Length
1   seq1    seq11   1   
2   seq1    seq11   11  
3   seq3    seq33   21  
4   seq3    seq33   14  

I want to loop though colA first, get the relevant colB value, and check if there are any other occurrences of the same value.
For example in colB (seq11) there are 2 occurrences of colA(seq1), this time I have to combine those and output the sum of the length. Similar to this:

ID  colA  colB   Length
1   seq1  seq11  12
2   seq3  seq33  35

I am a bit Java guy, but because my colleague has written everything in PHP and this will be just an adding, I need a PHP solution.
With Java I would have used hashmap, so that I would have the colA data once and just increment the value of “Length Column”.

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I tried this query in order to group by occurences:

SELECT COUNT(*) SeqName FROM SeqTable GROUP BY SeqName HAVING COUNT(*)>0;

Answer 1

In PHP you can use an array like an hash map

$array = Array();
$array['seq1'] = Array();
$array['seq1']['seq11'] = 0;
$array['seq1']['seq11']++;

Or you can use an SQL query like this one:

select id,colA,colB,sum(Length) as Length from {tableName} group by colA,colB order by colA, colB;