SQLite count, group and order by count

问题:

I have a table that looks like this:

FOO  BAR  BAZ
----+----+----
foo1 bar1 baz1
foo2 bar3 baz2
foo3 bar1 baz3
foo4 bar1 baz4
foo5 bar3 baz5
foo6 bar1 baz6
foo7 bar2 baz7

And as a result I would like to get the count of how many times each bar appeared in the table.. so, the output I'm looking for looks like this:

BAR   COUNT
-----+-----
bar1    4
bar3    2
bar2    1

Can I do a query for something like this in SQLite? I guess it should be pretty easy, but I am not an SQL programmer by any means, and I just need this simple query as a part of a python script.. Thank you.

回答1:

SELECT foo, count(bar) FROM mytable GROUP BY bar ORDER BY count(bar) DESC;

The group by statement tells aggregate functions to group the result set by a column. In this case "group by bar" says count the number of fields in the bar column, grouped by the different "types" of bar.

A better explanation is here: http://www.w3schools.com/sql/sql_groupby.asp