performance of Using QSqlQuery to access table containing blob coloumn

[silentyears]

Hi,
As subject, i use QSqlQuery to access tableA which contains column storing blob data as follows,

QSqlQuery query("SELECT * FROM tableA");
     while (query.next()) {
         i++;
     }

QSqlQuery query("SELECT * FROM tableA");
     while (query.next()) {
         i++;
     }

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The speed of query is too slow which need about 5s to execute whole "while" loop, is there any idea to improved it? How to deal with blob?
Thanks!