1.LENGTH() 长度
select length(id) from merchant where id=221; 3
2.REPLACE(,[,]) 替换
c1,c2,c3都是字符串，函数用c3代替出现在c1中的c2后返回。
select REPLACE('uptown','up','down') from dual
downtown
3.SUBSTR(,＜i＞[,]) 截取
c1为一字符串，i,j为整数，从c1的第i位开始返回长度为j的子字符串，如果j为空，则直到串的尾部。
select SUBSTR(id,1,2) from merchant where id=221; select SUBSTR(id,2,2) from merchant where id=221; 22 21
4.SYADATE
函数没有参数，返回当前日期和时间。
select sysdate from dual;
5.TO_CHAR([[,)和TO_DATE([,）
select * from wechat_trans_info where trans_status =? and to_char(trans_time,'yyyy-MM-dd') = ? and acq_enname='SPD' order by trans_time ";
Object[] params = {"SUCCESS",transDate};
return dao.find(WechatTransInfo.class,sql,params);
and sai.create_time >= to_date (?,'yyyy-MM-dd hh24:mi:ss')
6.
UID 该函数没有参数，返回唯一标示当前数据库用户的整数。 select uid from dual; 121 USER 返回当前用户的用户名 select user from dual; QRPAY
7.trunc
select trunc(sysdate)-1 from dual; 2017/6/29 今天为2017/6/30，获得的是昨天的日期
8.round 保留几位小数
wechat_merchant_rate=0.002select round(wechat_merchant_rate,2) from wechat_merchant where id=869;select round(wechat_merchant_rate,3) from wechat_merchant where id=869;0.000.002
