REGR_SLOPE()

Overview

The REGR_SLOPE() aggregate function calculates the slope of the regression line for a linear relationship between a dependent variable (y) and an independent variable (x). The slope represents the rate of change in y for every unit increase in x. This function is used in regression analysis to quantify the strength and direction of a linear relationship.

Syntax

The syntax for this function is as follows:

REGR_SLOPE(y, x)

Parameters

• y: variable being predicted
• x: variable used for prediction

Example

For the needs of this section, we’re going to use a simplified version of the film table from the Pagila database, containing only the title, length and rating columns. The complete schema for the film table can be found on the Pagila database website.

DROP TABLE IF EXISTS film;
CREATE TABLE film (
  title text NOT NULL,
  length int,
  rating int
);
INSERT INTO film(title, length, rating) VALUES
  ('ATTRACTION NEWTON', 83, 5),
  ('CHRISTMAS MOONSHINE', 150, 7),
  ('DANGEROUS UPTOWN', 121, 4),
  ('KILL BROTHERHOOD', 54, 3),
  ('HALLOWEEN NUTS', 47, 5),
  ('HOURS RAGE', 122, 7),
  ('PIANIST OUTFIELD', 136, 7),
  ('PICKUP DRIVING', 77, 3),
  ('INDEPENDENCE HOTEL', 157, 7),
  ('PRIVATE DROP', 106, 4),
  ('SAINTS BRIDE', 125, 3),
  ('FOREVER CANDIDATE', 131, 7),
  ('MILLION ACE', 142, 5),
  ('SLEEPY JAPANESE', 137, 4),
  ('WRATH MILE', 176, 7),
  ('YOUTH KICK', 179, 7),
  ('CLOCKWORK PARADISE', 143, 5);

The query below uses the REGR_SLOPE() function to calculate the slope of the regression line for valid pairs of rating and length:

SELECT
    REGR_SLOPE(rating, length) AS Slope
FROM film;

By running the above code, we will get the following output:

        slope         
----------------------
 0.025985694391063227
(1 row)