-- 1.获取当前日期时间
SELECT SYSDATE() FROM DUAL;
SELECT CURRENT_DATE() FROM DUAL;
-- 获取时间戳
SELECT CURRENT_TIMESTAMP() FROM DUAL;
-- 2,日期的截取
-- 获取到当前日期时间所在的年份
select extract(year FROM SYSDATE()) FROM DUAL;
select extract(month FROM SYSDATE()) FROM DUAL;
select extract(DAY FROM SYSDATE()) FROM DUAL;
-- 3.日期的截断,这个四舍五入没用
select round(SYSDATE(),'year') FROM DUAL;
select TRUNCATE(SYSDATE(),'year')FROM DUAL;
--
select ename,empno months_between(sysdate(),hiredate) months FROM t_emptest;
SELECT * FROM t_emptest;
SELECT SYSDATE() FROM DUAL;
SELECT * FROM t_emptest WHERE SAL = '3000';
SELECT * FROM t_emptest WHERE SAL = 3000;
SELECT 100 + 2000 FROM DUAL;
SELECT '100' + 2000 FROM DUAL;
SELECT 100 + CAST('200' AS INT) FROM DUAL;
SELECT CAST(100 AS VARCHAR)+100 FROM DUAL;
SELECT CAST(100 AS char) + 100 FROM DUAL;
select cast(date_cloumn as signed) as date from t_date ;
select cast(timstamp_cloumn as time) as date from t_date ;
-- 获取到最大的
select greatest(10,'101',9) from dual;
-- 找到最小的，按照accii码值来比较
select least('中','ABC','ab',1000) from dual
select 1 + null from dual;