A function to calculate Lower bound of Wilson score confidence interval for a Bernoulli parameter @see http://www.evanmiller.org/how-not-to-sort-by-average-rating.html For this formula the interval is set at 95%

wilson.sql

CREATE FUNCTION wilson(stars INT, total INT)
RETURNS REAL DETERMINISTIC
RETURN IF (
	total,
	(
		(stars + 1.9208) / total - 
		1.96 * SQRT((stars * (total-stars)) / total + 0.9604) / total
	) / (1 + 3.8416 / total), 
	0
)