Given a table events with the following structure:

create table events $($

sensor$\_$id integer not null,

event$\_$type integer not null,

value float not null,

time timestamp not null,

$)$:

Write an SQL query that returns a set of all sensors $($sensors$\_$id$)$ with. the number of different event types $($event$\_$type$)$ registered by each of them, ordered by sensor$\_$id $($in ascending order$)$

For example, given the following data:

sensor$\_$id event$\_$type value time

$223\mathrm{.}452014-02-1312$:$42$:$00$

$24-149\mathrm{.}922014-02-1312$:$42$:$00$

$224\mathrm{.}122014-02-1312$:$54$:$39$

$323\mathrm{.}472014-02-1312$:$42$:$00$

$2324\mathrm{.}542014-02-1313$:$32$:$36$

your query should return the following rowset:

sensor$\_$id types

$23$

$31$

the names of the columns in the rowset dont matter, but their order does