ORACLE to_char(),to_date()Ó÷¨

to_date() function
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D Ò»ÖÜÖеÄÐÇÆÚ¼¸ 
DAY ÌìµÄÃû×Ö£¬Ê¹ÓÿոñÌî³äµ½9¸ö×Ö·û 
DD ÔÂÖеĵڼ¸Ìì 
DDD ÄêÖеĵڼ¸Ìì 
DY ÌìµÄ¼òдÃû 
IW ISO±ê×¼µÄÄêÖеĵڼ¸ÖÜ 
IYYY ISO±ê×¼µÄËÄλÄê·Ý 
YYYY ËÄλÄê·Ý 
YYY,YY,Y Äê·ÝµÄ×îºóÈý룬Á½Î»£¬Ò»Î» 
HH Сʱ£¬°´12Сʱ¼Æ 
HH24 Сʱ£¬°´24Сʱ¼Æ 
MI ·Ö 
SS Ãë 
MM Ô 
Mon Ô·ݵļòд 
Month Ô·ݵÄÈ«Ãû 
W ¸ÃÔµĵڼ¸¸öÐÇÆÚ 
WW ÄêÖеĵڼ¸¸öÐÇÆÚ    
 
2.ÈÕÆÚʱ¼ä¼ä¸ô²Ù×÷
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select sysdate,sysdate - interval '7' MINUTE from dual
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select sysdate - interval '7' hour from dual
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select sysdate - interval '7' day from dual
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select sysdate,sysdate - interval '7' month from dual
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select sysdate,sysdate - interval '7' year from dual
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select sysdate,sysdate - 8 *interval '2' hour from dual
 
to_char() function
The following are number examples for the to_char function.
to_char(1210.73, '9999.9')
would return '1210.7'
to_char(1210.73, '9,999.99')
would return '1,210.73'
to_char(1210.73, '$9,999.00')
would return '$1,210.73'
to_char(21, '000099')
would return '000021'
 
The following is a list of valid parameters when the to_char function is used to convert a date to a string. These parameters can be used in many combinations.
 
Parameter
Explanation
YEAR
Year, spelled out
YYYY
4-digit year
YYY
YY
Y
Last 3, 2, or 1 digit(s) of year.
IYY
IY
I
Last 3, 2, or 1 digit(s) of ISO year.
IYYY
4-digit year £â£á£ó£åd on the ISO standard
Q
Quarter of year (1, 2, 3, 4; JAN-MAR = 1).
MM
Month (01-12; JAN = 01).
MON
Abbreviated name of month.
MONTH
Name of month, padded with blanks to length of 9 characters.
RM
Roman numeral month (I-XII; JAN = I).
WW
Week of year (1-53) where week 1 starts on