How many reviews by people between 30 and 50 years include the word 'great'?
between 30 and 50 years refers to age BETWEEN 30 AND 50; include the word great refers to Review like '%Great%';
SELECT COUNT(T1.Reviews) FROM reviews AS T1 INNER JOIN client AS T2 ON T1.district_id = T2.district_id WHERE T2.age BETWEEN 30 AND 50 AND T1.Reviews LIKE '%great%'