Oracle's date functions

a system time

1. Grammar

SYSDATE

Default format: DD-MON-RR (day month year)

2. Examples

1. SQL>select sysdate from dual;
3. SYSDATE
4. --------------
5. 02-7月-17

two-day operation

1. Grammar

ADD_MONTHS(date,i): Returns the month added to the specified date.

i can be any integer, if i is a decimal, the integer part is truncated

If i is negative, it is equivalent to subtracting the month from the original date.

NEXT_DAY （date，char）

If the value of char is 'Monday', returns the next Monday hour of the date specified by date.

LAST_DAY(date): Returns the last day of each month.

MONTH_BETWEEN(date1,date2)

EXTRACT(date from datetime)

2. Examples

1. SQL>select add_months(sysdate,3),add_months(sysdate,-3)from dual;
3. ADD_MONTHS(SYS ADD_MONTHS(SYS
4. ----------------------------
5. 02-10月-1702-4月-17
7. SQL>select next_day(sysdate,'星期一')from dual;
9. NEXT_DAY(SYSDA
10. --------------
11. 03-7月-17
13. SQL>select next_day(sysdate,'星期日')from dual;
15. NEXT_DAY(SYSDA
16. --------------
17. 09-7月-17
19. SQL>select last_day(sysdate)from dual;
21. LAST_DAY(SYSDA
22. --------------
23. 31-7月-17
25. SQL>select month_betweens('20-5月-15','10-1月-15')from dual;
26. select month_betweens('20-5月-15','10-1月-15')from dual
27. *
28. 第1行出现错误:
29. ORA-00904:"MONTH_BETWEENS":标识符无效
32. SQL>select months_between('20-5月-15','10-1月-15')from dual;
34. MONTHS_BETWEEN('20-5月-15','10-1月-15')
35. ---------------------------------------
36. 4.32258065
38. SQL>select extract(year from sysdate)from dual;
40. EXTRACT(YEARFROMSYSDATE)
41. ------------------------
42. 2017
44. SQL>select extract(month from sysdate)from dual;
46. EXTRACT(MONTHFROMSYSDATE)
47. -------------------------
48. 7
50. SQL>select extract(day from sysdate)from dual;
52. EXTRACT(DAYFROMSYSDATE)
53. -----------------------
54. 2
57. SQL>select extract(hour from timestamp '2017-10-1 17:24:34')from dual;
59. EXTRACT(HOURFROMTIMESTAMP'2017-10-117:24:34')
60. ---------------------------------------------
61. 17
63. SQL>