earthhour的专栏

select date_format(t.login_date,'%Y-%m-%d') AS 日期,COUNT(DISTINCT t.user_id) as 人数 from user_login t group by date_format(t.login_date,'%Y-%m-%d') ORDER BY t.login_date ASC; 统计系统每天登录人数，去除重复登录

MERGE INTO USING ON () WHEN MATCHED THEN DELETE WHEN NOT MATCHED THEN [LOG ERRORS ];  MERGE INTO table a USING ( SELECT '1' as name FROM dual ) b ON (a.name = b.name) WHEN MATC

update DISTRICT set DISTRICT_NAME = replace(DISTRICT_NAME,'-','') 替换DISTRICT_NAME字段数据中的中横线“-”