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Nejúčinnější (pomocí over()).
select Grade, count(*) * 100.0 / sum(count(*)) over() from MyTable group by Grade
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Universal (jakákoli verze SQL).
select Grade, count(*) * 100.0 / (select count(*) from MyTable) from MyTable group by Grade;
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S CTE, nejméně efektivní.
with t(Grade, GradeCount) as ( select Grade, count(*) from MyTable group by Grade ) select Grade, GradeCount * 100.0/(select sum(GradeCount) from t) from t;