请教一条SQL语句怎么写



[解决办法]
我用的是Oracle数据库：

SELECT AGE_SECTION, COUNT (1)
FROM (SELECT CASE
WHEN AGE >= 20 AND AGE < 40
THEN '20-40'
WHEN AGE >= 40 AND AGE < 50
THEN '40-50'
WHEN AGE >= 50
THEN '>=50'
END AGE_SECTION
FROM KS)
GROUP BY AGE_SECTION