Selecting the distinct values from three columns w

问题:

I have a table with one numeric value (n) and three string values (a,b,c). How do I query this table so that I get only distinct values of (a,b,c) and if there are duplicates, take the maximum of the corresponding set of n values?

回答1:

select max(n), a, b, c
from mytable
group by a, b, c

回答2:

Use GROUP BY:

select a, b, c, max(n) 
from table 
group by a, b, c;

This will show only unique or distinct sets of a, b, c and show the maximum n found in that set.

MAX is an aggregate function designed for use with GROUP BY. Other potentially useful aggregate functions include MIN, AVERAGE, and COUNT.