例：
SELECT
CASE
WHEN (store_size <= (100)::NUMERIC)
THEN ‘小店‘::TEXT
WHEN (store_size >= (200)::NUMERIC)
THEN ‘大店‘::TEXT
ELSE ‘中店‘::TEXT
END AS store_area_level
FROM SALE
PostgreSQL条件表达式 case when then end
原文：https://www.cnblogs.com/telwanggs/p/10751578.html