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Tips on reshaping data, pivot-like?
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tipspivotreshapinglikedata
Problem
I have a table of levels and years that looks roughly like this:
I can capture totals for each level and year with a pretty basic
That gives me a fairly tidy summary of the demo data:
My actual data is a lot bigger, and I'd like to be able to see it in a summary table that looks something more like this:
Is there a straightforward way to query a pivot-like view like this? For a much wider range of ranks and years?
INSERT INTO demo(first_name, rank, year) AS VALUES
('Peter',2,2017), ('Robert',3,2016), ('Evelyn',2,2017),
('Rand',3,2017), ('Kofi',3,2017), ('Daniel',3,2016), ('Leonard',1,2017),
('Mary',1,2017), ('Frank',1,2017), ('John',3,2017), ('Mary',1,2016),
('Gilbert',3,2016), ('Quince',2,2017), ('David',3,2017), ('Louis',2,2017),
('Felipe',2,2016), ('Alfonso',1,2017), ('Elise',3,2016), ('Jorge',3,2017),
('Mary',3,2016), ('Jasvant',2,2017), ('Paul',3,2017), ('Richard',2,2017),
('Christopher',2,2017), ('Johannes',2,2016), ('Nasser',3,2016), ('Bruce',3,2017),
('John',3,2016), ('Frederic',3,2016);I can capture totals for each level and year with a pretty basic
COUNT(): SELECT rank, COUNT(*), year
FROM demo
GROUP BY rank, year
ORDER BY year, rank;That gives me a fairly tidy summary of the demo data:
Rank Count Year
1 1 2016
2 2 2016
3 8 2016
1 4 2017
2 7 2017
3 7 2017My actual data is a lot bigger, and I'd like to be able to see it in a summary table that looks something more like this:
Rank 2016 2017
1 1 4
2 2 7
3 8 7Is there a straightforward way to query a pivot-like view like this? For a much wider range of ranks and years?
Solution
You can pivot your data using crosstab, but as usual it requires a well-known column's name.
First you should install tablefunc module.
Then you can call a crosstab with
rk | 2016 | 2017
-: | ---: | ---:
1 | 1 | 4
2 | 2 | 7
3 | 8 | 7
dbfiddle here
First you should install tablefunc module.
CREATE EXTENSION tablefunc;Then you can call a crosstab with
SELECT * FROM
crosstab('SELECT rank, year::INT, COUNT(*)::INT ct FROM demo
GROUP BY 1, 2 ORDER BY 1, 2')
AS ct(rk INT, "2016" INT, "2017" INT)rk | 2016 | 2017
-: | ---: | ---:
1 | 1 | 4
2 | 2 | 7
3 | 8 | 7
dbfiddle here
Code Snippets
CREATE EXTENSION tablefunc;SELECT * FROM
crosstab('SELECT rank, year::INT, COUNT(*)::INT ct FROM demo
GROUP BY 1, 2 ORDER BY 1, 2')
AS ct(rk INT, "2016" INT, "2017" INT)Context
StackExchange Database Administrators Q#201929, answer score: 6
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