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Overview

The REGR_SXX() aggregate function calculates the sum of squares of deviations for the independent variable (x) in a linear regression analysis. This value represents the variability of the independent variable and is a key component in calculating the slope and other regression statistics.

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Syntax

The syntax for this function is as follows:

REGR_SXX(y, x)

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Parameters

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

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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,
  rating int,
  length 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_SXX() function to calculate the sum of squares of deviations for the independent variable length:

SELECT
    REGR_SXX(rating, length) AS SumOfSquaresX
FROM film;

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

  sumofsquaresx   
------------------
 23569.5294117647
(1 row)
REGR_SLOPEREGR_SXY