小技巧1--获取日期中的指定部分

sql:

SELECT EXTRACT(YEAR FROM SYSDATE) FROM DUAL; return Current Year

SELECT EXTRACT(MONTH FROM SYSDATE) FROM DUAL; return Current Month

SELECT EXTRACT(DAY FROM SYSDATE) FROM DUAL; return Current Day

SELECT EXTRACT(HOUR FROM SYSDATE) FROM DUAL;Error

Correct:SELECT EXTRACT(HOUR FROM TIMESTAMP '2005-10-10 10:10:10') FROM DUAL;

SELECT EXTRACT(MINUTE FROM SYSDATE) FROM DUAL;Error

Correct:SELECT EXTRACT(MINUTE FROM TIMESTAMP '2005-10-10 10:10:10') FROM DUAL;

EXTRACT()函数的使用说明,英文部分有个很重要的部分.就是extract 抽取年月日部分和时分部分的使用方法是不同的.

EXTRACT(YEAR FROM SYSDATE)中FROM 的下一个参数是日期类型的时候可以抽取年月日.就是说这个参数是日期类型的时候就可以抽取年\月\日,而抽取不了时\分部分.抽取时分部分得在FROM 后面加带TIMESTAMP 且后面加时间字符

如果真要从日期类型的字段中抽取时\分部分用to_char() 函数就可以了.比如to_char(日期类型,'hh24:mi')

java

GregorianCalendar gc = new GregorianCalendar();

int day = gc.get(Calendar.DAY_OF_MONTH);

GregorianCalendar gc = new GregorianCalendar();

gc.setTime(Calendar.getInstance().getTime());

System.out.println("gc.getTime()="+gc.getTime());

int day = gc.get(Calendar.DAY_OF_MONTH);

int month = gc.get(Calendar.MONTH);

String str_date = new SimpleDateFormat("yyyy-MM").format(gc.getTime());

gc.add(GregorianCalendar.MONTH, -1);//在月份上减1

int month1 = gc.get(Calendar.MONTH);

String str_date1 = new SimpleDateFormat("yyyy-MM").format(gc.getTime());

gc.add(GregorianCalendar.MONTH, -1);//在月份上减2

int month2 = gc.get(Calendar.MONTH);

String str_date2 = new SimpleDateFormat("yyyy-MM").format(gc.getTime());