SQL count when equation of two columns are true - sql

Question

I have a sheet with rows (id and year). See below:
id
year
101
2002
101
2006
101
2010
101
2014
101
2018
102
2002
102
2006
102
2010
102
2014
103
2010
I simply want to regroup and reformat my table to look like this:
id
2002
2006
2010
2014
2018
101
1
1
1
1
1
102
1
1
1
1
0
103
0
0
1
0
0
In other words, whenever there is an id with a specific year it will show as a "1" in a field corresponding to that year. Note, that in the sheet there are no other years than the ones above.
I have managed to get the sheet reformatted by
select
id,
null as '2002', null as '2006', null as '2010',
null as '2014', null as '2018'
from
year_sheet
order by
id
But how to count and fill in the values for each year I don't find any solution.
Can someone help?
Thanks

Answer 1

You can use conditional aggregation:
SELECT id
, COUNT(CASE WHEN year = 2002 THEN 1 END) AS "2002"
, COUNT(CASE WHEN year = 2006 THEN 1 END) AS "2006"
, COUNT(CASE WHEN year = 2010 THEN 1 END) AS "2010"
, COUNT(CASE WHEN year = 2014 THEN 1 END) AS "2014"
, COUNT(CASE WHEN year = 2018 THEN 1 END) AS "2018"
FROM t
GROUP BY id
ORDER BY id
SQL Fiddle

Answer 2

try using case statement (Conditional statements)
select id,
case when year=2002 then 1 else 0 end as "2002",
case when year=2006 then 1 else 0 end as "2006",
case when year=2010 then 1 else 0 end as "2010",
case when year=2014 then 1 else 0 end as "2014",
case when year=2018 then 1 else 0 end as "2018"
from table
order by id
assuming that you would like to make the flags as 1 and 0 if the year appears for the id (for every id year appears only once).
In case if you want to count them (for eery id year appears more than once) then try using sum(case when....) as follows
select id,
sum(case when year=2002 then 1 else 0 end)as "2002",
sum(case when year=2006 then 1 else 0 end)as "2006",
sum(case when year=2010 then 1 else 0 end)as "2010",
sum(case when year=2014 then 1 else 0 end)as "2014",
sum(case when year=2018 then 1 else 0 end)as "2018"
from table
group by id
order by id