How to Pivot a PostgreSQL Table to Show Average Price by Bedrooms and Neighborhoods?

Creating a pivot table in PostgreSQL

PostgreSQL uses the crosstab() function to create pivot tables. This function accepts two inputs: a query and a list of column names. The query should produce a result set with two columns: one for row headers and one for data values. The list of column names should correspond to the columns in the result set that should be pivoted.

Question:

Consider the following table named listings:

id	neighborhood	bedrooms	price
1	downtown	0	189000
2	downtown	3	450000
3	riverview	1	300000
4	riverview	0	250000
5	downtown	1	325000
6	riverview	2	350000

How to create a pivot table query, with number of bedrooms as columns and neighborhood as rows, showing the average price per bedroom?

The required output should be formatted as follows:

neighborhood	0	1	2	3
downtown	189000	325000	-	450000
riverview	250000	300000	350000	-

Solution:

To create a pivot table, follow these steps:

1. Calculate the average: Use the avg() aggregate function to calculate the average price for each neighborhood and number of bedrooms combination.

   <code class="language-sql"> SELECT
      neighborhood,
      bedrooms,
      avg(price)
    FROM
      listings
    GROUP BY
      1, 2
    ORDER BY
      1, 2;</code>

2. Provide the results to crosstab(): Provide the results of the previous query to the crosstab() function. Use $$...$$ to specify an array of values ​​for column names. You can convert the average to an integer to get a rounded result.

   <code class="language-sql"> SELECT
      *
    FROM
      crosstab(
        'SELECT
          neighborhood,
          bedrooms,
          avg(price)::int
        FROM
          listings
        GROUP BY
          1, 2
        ORDER BY
          1, 2;',
        $$SELECT unnest('{0,1,2,3}'::int[])$$
      ) AS ct (
        "neighborhood" text,
        "0" int,
        "1" int,
        "2" int,
        "3" int
      );</code>

This query generates the required pivot table by pivoting on the average price of different bedrooms within each neighborhood.

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