Re: Distinct or Group by which is faster

[Peter Brawley]

Those queries are not logically equivalent.

The first will return exactly one row for each combination of id,name,age values found.

The second will return exactly one row for each value of id found, along with name and age values selected arbitrarily from those found for each id.

The logical equivalent to select distinct id,name,age from ... would be select id,name,age from ... group by id,name,age.

Which is faster depends on what else is in the query. In some cases, MySQL might use execute select Distinct a,b,c as Group By a,b,c.