-- Database schema
| playstore : App [ TEXT ] , Category [ TEXT ] , Rating [ REAL ] , Reviews [ INTEGER ] , Size [ TEXT ] , Installs [ TEXT ] , Type [ TEXT ] , Price [ TEXT ] , Content Rating [ TEXT ] , Genres [ TEXT ] | user_reviews : App [ TEXT ] user_reviews.App = playstore.App , Translated_Review [ TEXT ] , Sentiment [ TEXT ] , Sentiment_Polarity [ TEXT ] , Sentiment_Subjectivity [ TEXT ] |
-- -- What is the percentage for free application with a rating 4.5 and above have not been updated since 2018?

SELECT CAST(SUM(CASE WHEN SUBSTR('Last Updated', -4) > '2018' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(App) PER FROM playstore WHERE Type = 'Free' AND Rating >= 4.5;