SQL汇总去重数据进化

1、正常GROUP汇总去重写法

SELECT COUNT(1) FROM(
　　SELECT COUNT(1) FROM cookie_used_t WHERE clevel>=0 AND clevel<4 GROUP BY cuid
)t;

2、正常DISTINCT 汇总去重写法

SELECT COUNT(1) FROM(
　　SELECT DISTINCT cuid FROM cookie_used_t WHERE clevel>=0 AND clevel<4
)t;

SELECT COUNT(1) FROM(
　　SELECT DISTINCT(cuid) FROM cookie_used_t WHERE clevel>=0 AND clevel<4
)t;

3、DISTINCT 汇总去重改造

SELECT COUNT(DISTINCT cuid) FROM cookie_used_t WHERE clevel>=0 AND clevel<4;