The question: Find the capital and the name where the capital is an extension of name of the country. Note that the capital must be longer than the name (Mexico-City compared to Luxembourg) This is my work, but it’s incorrect
SELECT name , capital FROM world WHERE capital LIKE concat(name, '%')
To get the extension you can use REPLACE function which in following query replacing the ‘name’ of country from ‘capital’ to null.
SELECT name , REPLACE(capital,name,'') FROM world WHERE capital LIKE concat(name, '_%');