How to create a pivot table in PostgreSQL - sql

Question

I am looking to essentially create a pivot view using PostgreSQL, such that the table below:
Column A
Column B
Happy
Sad
Sad
Happy
Happy
Sad
becomes
Count
Column A
Column B
Happy
2
1
Sad
1
2
I've been able to use case/when operators far enough such that I can see the counts under independent columns,
SELECT
COUNT(CASE WHEN column1 = 'Happy' THEN 1 END) AS column1_Happy_count,
COUNT(CASE WHEN column1 = 'Sad' THEN 1 END) AS column1_Sad_count,
COUNT(CASE WHEN column2 = 'Happy' THEN 1 END) AS column2_Happy_count,
COUNT(CASE WHEN column2 = 'Sad' THEN 1 END) AS column2_Sad_count,
COUNT(CASE WHEN column3 = 'Happy' THEN 1 END) AS column3_Happy_count,
COUNT(CASE WHEN column3 = 'Sad' THEN 1 END) AS column3_Sad_count
FROM your_table;
but am missing the step to essentially each the pair of columns vertically.
I'm unable to use extensions such as tablefunc and crosstab.

Answer 1

Try this:
CREATE TABLE my_table (
column_a varchar(10),
column_b varchar(10)
);
INSERT INTO my_table (column_a, column_b)
VALUES ('Happy', 'Sad'),
('Sad', 'Happy'),
('Happy', 'Sad'),
('Good', 'Bad');
WITH DataSource (col, val) AS
(
SELECT 'a', column_a
FROM my_table
UNION ALL
SELECT 'b', column_b
FROM my_table
)
SELECT uniq.val AS "Count"
,MAX(case when counts.col = 'a' then counts end) AS "Column A"
,MAX(case when counts.col = 'b' then counts end) AS "Column B"
FROM
(
SELECT DISTINCT val
FROM DataSource
) uniq
INNER JOIN
(
SELECT col
,val
,COUNT(*) counts
FROM DataSource
GROUP BY col
,val
) counts
ON uniq.val = counts.val
GROUP BY uniq.val
will give you this:

Answer 2

You may aggregate for ColumnA, aggregate for ColumnB then do a full join as the following:
select coalesce(A.ColumnA ,B.ColumnB) as "Count",
A.cnt as "Column A",
B.cnt as "Column B"
from
(
select ColumnA, count(*) cnt
from tbl_name
group by ColumnA
) A
full join
(
select ColumnB, count(*) cnt
from tbl_name
group by ColumnB
) B
on A.ColumnA = B.ColumnB
If the distinct values in ColumnA are the same as the distinct values of ColumnB then you can use join instead of the full join.
See demo.