oracle Extract 函数

1. //oracle中extract()函数从oracle 9i中引入,用于从一个date或者interval类型中截取到特定的部分
2. //语法如下：
3. EXTRACT (
4. { YEAR | MONTH | DAY | HOUR | MINUTE | SECOND }
5. | { TIMEZONE_HOUR | TIMEZONE_MINUTE }
6. | { TIMEZONE_REGION | TIMEZONE_ABBR }
7. FROM { date_value | interval_value } )
8. //我们只可以从一个date类型中截取 year,month,day(date日期的格式为yyyy-mm-dd);
9. //我们只可以从一个 timestamp with time zone 的数据类型中截取TIMEZONE_HOUR和TIMEZONE_MINUTE;
10. select extract(year from date'2011-05-17') year from dual;
11. YEAR
12. ----------
13. 2011
14. select extract(month from date'2011-05-17') month from dual;
15. MONTH
16. ----------
17. 5
18. select extract(day from date'2011-05-17') day from dual;
19. DAY
20. ----------
21. 17
22. //获取两个日期之间的具体时间间隔，extract函数是最好的选择
23. select extract(day from dt2-dt1) day
24. ,extract(hour from dt2-dt1) hour
25. ,extract(minute from dt2-dt1) minute
26. ,extract(second from dt2-dt1) second
27. from (
28. select to_timestamp('2011-02-04 15:07:00','yyyy-mm-dd hh24:mi:ss') dt1
29. ,to_timestamp('2011-05-17 19:08:46','yyyy-mm-dd hh24:mi:ss') dt2
30. from dual)
31. /
32. DAY HOUR MINUTE SECOND
33. ---------- ---------- ---------- ----------
34. 102 4 1 46
35. --
36. select extract(year from systimestamp) year
37. ,extract(month from systimestamp) month
38. ,extract(day from systimestamp) day
39. ,extract(minute from systimestamp) minute
40. ,extract(second from systimestamp) second
41. ,extract(timezone_hour from systimestamp) th
42. ,extract(timezone_minute from systimestamp) tm
43. ,extract(timezone_region from systimestamp) tr
44. ,extract(timezone_abbr from systimestamp) ta
45. from dual
46. /
47. YEAR MONTH DAY MINUTE SECOND TH TM TR TA
48. ---------- ---------- ---------- ---------- ---------- ---------- ---------- --------- ----------
49. 2011 5 17 7 14.843 8 0 UNKNOWN UNK
50. //