[重庆思庄每日技术分享]-oracle12c新特性 去重统计函数APPROX_COUNT_DISTINCT

Note:

The APPROX_COUNT_DISTINCT function is available starting with Oracle Database 12c Release 1 (12.1.0.2).

用例：

求scott.emp表中一共有多少个部门

11g:

SELECT COUNT(DISTINCT deptno) AS cnt FROM scott.emp

12c:

SELECT APPROX_COUNT_DISTINCT(deptno) AS cnt FROM scott.emp