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Neeraj Bisht authored
CONTAINING NULL Problem:- In MySQL, We can obtain the number of distinct expression combinations that do not contain NULL by giving a list of expressions in COUNT(DISTINCT). However rows with NULL values are incorrectly included in the count when loose index scan is used. Analysis:- In case of loose index scan, we check whether the field is null or not and increase the count in Item_sum_count::add(). But there we are checking for the first field in COUNT(DISTINCT), not for every field. This is causing an incorrect result. Solution:- Check all field in Item_sum_count::add(), whether there values are null or not. Then only increment the count. ****** Bug#17222452 - SELECT COUNT(DISTINCT A,B) INCORRECTLY COUNTS ROWS CONTAINING NULL Problem:- In MySQL, We can obtain the number of distinct expression combinations that do not contain NULL by giving a list of expressions in COUNT(DISTINCT). However rows with NULL values are incorrectly included in the count when loose index scan is used. Analysis:- In case of loose index scan, we check whether the field is null or not and increase the count in Item_sum_count::add(). But there we are checking for the first field in COUNT(DISTINCT), not for every field. This is causing an incorrect result. Solution:- Check all field in Item_sum_count::add(), whether there values are null or not. Then only increment the count.
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