MySql - Using variables in select query and where condition gives one more additional row

Question

I am using variables in select query to calculate a value and based on the value I have added where condition in query.

What my problem in it gives addtional one more row whatever field value is.

For example if the field value is 1 on all rows in that table then it gives 20 plus additional one more row 21.

Kindly help in solving this issue.

How to add condtion based on value calculated as I can't use SUM, it will aggregate and returns only one value.

Below is sample query I use.

SET @var = 0;
SELECT  @var := @var + field FROM table1 WHERE  @var <= 20

Answer 1

MySql version 5.5.45

Check for

SELECT t1.(fieldset)
FROM source_table t1
JOIN source_table t2 ON t1.ordering_field <= t2.ordering field
GROUP BY t1.(fieldset)
HAVING SUM(t2.amount_field) <= @needed_sum
ORDER BY SUM(t2.amount_field) DESC [LIMIT 1]