Suppose I have a table in Postgres called listings
that looks like this:
id neighborhood bedrooms price 1 downtown 0 256888 2 downtown 1 334000 3 riverview 1 505000 etc.
How do I write a crosstab query that shows the average price per bedrooms as the columns and neighborhoods as the rows?
The output of the query should look something like this (numbers are made up, columns are the bedrooms):
0 1 2 3 riverton 250000 300000 350000 - downtown 189000 325000 - 450000
SQL Server provides PIVOT and UNPIVOT functions to create pivot tables. Unfortunately, PostgreSQL does implement them. However, it provides crosstab function from tablefunc extensions which is equivalent to PIVOT .
The crosstab function produces one output row for each consecutive group of input rows with the same row_name value. The output row_name column, plus any “extra” columns, are copied from the first row of the group. The output value columns are filled with the value fields from rows having matching category values.
First compute the average with the aggregate function avg():
SELECT neighborhood, bedrooms, avg(price) FROM listings GROUP BY 1,2 ORDER BY 1,2
Then feed the result to the crosstab()
function as instructed in great detail in this related answer:
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