Oracle: time type

Oracle The type of time in

1、Oracle The only time type in is date and TIMESTAMP,TIMESTAMP It's better than date More precise types
    ⑴DATE type ：ORACLE The most common date type , It can save dates and times , Common date processing can use this type
    ⑵TIMESTAMP type ：ORACLE Common date types , It is associated with date Is the difference between the TIMESTAMP Type can not only save date and time , It can also save fractional seconds , The number of decimal places can be specified as 0-9, The default is 6 position

2、 The date time function is used to process time type data ,Oracle Many date related functions are provided in . Plus or minus dates , There are some rules for adding and subtracting dates
    ⑴ date - Numbers = date
    ⑵ date + Numbers = date ( God )
    ⑶ date - date = Numbers ( God )
    ⑷ stay Oracle in ,date Type can add or subtract days directly , And the months of addition and subtraction need to be used add_months function
    ⑸TIMESTAMP If the date type is added or subtracted from the value, it will be automatically converted to DATE type , In other words, fractional seconds will be automatically removed
    
3、 stay Oracle To be exact, a week begins on Sunday and ends on Saturday , The time difference is in days

 

Oracle Medium date type

date type ： It means year, month, day, hour, minute, second
    ⑴ The display format can be ：YYYY/MM/DD, It can also be for YYYY/MM/DD HH24:MI:SS
    ⑵ There is only one storage format ：YYYY/MM/DD HH24:MI:SS
    ⑶ namely ,date The value of type can have different display formats in the database graphical interface ( The specific display format is determined by the tool settings ), But the actual storage format is only one
    ⑷ When you only save the year, month and day ,date What's actually stored is ： Specific date 0 when 0 branch 0 second , stay plsql in , The display format is ：YYYY/MM/DD

example 1：

 

Oracle Medium timestamp type

1、date and timestamp They are all expressions of date and time , Only the accuracy of the two types is different , The former is accurate to seconds , The latter is accurate to decimal seconds

2、timestamp Short for timestamp . Time stamps can store centuries 、4 Year of the year 、 month 、 Japan 、 when ( With 24 Hour format )、 branch 、 second . And DATE Type comparison , Timestamps have the following advantages ：
    ⑴ Timestamps can store decimal places of seconds
    ⑵ Time stamps can store time zones

3、TIMESTAMP data type , It includes all DATE Information of data type: year, day, hour, minute and second , It also includes information about decimals and seconds . If you want to put the DATE Type conversion to TIMESTAMP type , Just use CAST function

 

 

Oracle Date format in

Format	describe
YYYY	Four digit year
YYY,YY,Y	The last three digits of the year 、 Two or one , The default is the current century
MM	01~12 Month number of
MONTH	Nine character month , Fill in the space on the right
MON	Three character month abbreviation
WW	The week of the year
D	Day of the week
DD	The day of the month
DDD	The day of the year
DAY	The full name of a nine character day , Fill in the blanks on the right
HH,HH12	Hours of the day ,12 Decimal notation
HH24	Hours of the day , The value is 00~23
MI	Minutes in an hour
SS	Seconds in a minute
SSSS	The number of seconds since midnight

 
 

 

Oracle Time function

sysdate

effect ：sysdate The time() function returns the time of the current system ( return date data type )

example 2： Inquire about

example 2_1： Insert

sql：insert into USER_INFO (ID,NAME,COUNTRY,DATE_TIME,TIMESTAMP) values(3,' Wang Wu ','China',sysdate,sysdate)

 

 

systimestamp

effect ： stay Oracle in ,systimestamp Function returns the current system date and time on the local database ( Including microseconds and time zones )

example 3： Inquire about

example 3_1： Insert

insert into USER_INFO (ID,NAME,COUNTRY,DATE_TIME,TIMESTAMP) values(4,' Li Liu ','China',systimestamp,systimestamp)

notes ： It can be seen that
sysdate The function is best used for date Data of type ,systimestamp Best used for timestamp Data of type . Of course, the two can be mixed , Just a little difference

 

 

to_date()

effect ： Convert character type into date type in a certain format

example 4： Query data

example 4_1： insert data

INSERT INTO USER_INFO (ID,NAME,CREATE_TIME,UPDATE_TIME) VALUES (9,' Small m',to_date('2020-07-29 18:00:00','yyyy-mm-dd hh24:mi:ss'),to_date('2020-07-29 18:00:00','yyyy-mm-dd hh24:mi:ss'))

notes ：
1、to_date() Only time type strings without millisecond level can be formatted
    ⑴to_date() Is used to convert string time to date type , The date type includes year, day, hour, minute and second

2、 If the field is a timetsmp Type of , Then the default millisecond level will be 0

3、Oracle Query data according to time Mysql There's a big difference
    ⑴ stay Mysql You can query directly according to the time string in ：SELECT * FROM roleinfo WHERE logintime = "2019-01-25";
    ⑵ stay Oracle When querying by time in , You must first convert the time string to date type

4、 Hour format ： No 24 when , The default is 12 hourly ,24 The hour format conversion needs to specify

example 4_2：

 

 

to_timestamp()

effect ： Convert character types into date timestamp types in a certain format (timestamp type )

example 4_3： Query data

example 4_4：

insert into user_info (ID,
NAME,
COUNTRY,
DATE_TIME,
TIMESTAMP,
DEPT_ID,
EMPLOYEE_NO,
LEADER_NO) values (6,'LL','yy',to_timestamp('2020-07-30 20:30:30.123400','yyyy-mm-dd hh24:mi:ss.ff'),to_timestamp('2020-07-30 20:30:30.123','yyyy-mm-dd hh24:mi:ss.ff3'),1,1,1)

 

 

to_char()

1、 effect ： Change the date to a character type in a certain format

2、 Formatting timestamp Time value of type , You can format milliseconds as needed
    ⑴ff：6 Bit millisecond value
    ⑵ff3：3 Bit millisecond value
    ⑶ It can also be done without a millisecond value
    
3、 If you are formatting a date Time value of type , So you can't add a millisecond parameter to the format string ,date There are no milliseconds in the type

4、date Type can only be accurate to seconds , To be precise in milliseconds , Need to use timestamp type

example 5： Query data

select to_char(CREATE_TIME,'yyyy-mm-dd hh24:mi:ss'),to_char(UPDATE_TIME,'yyyy-mm-dd hh24:mi:ss.ff') from USER_INFO where CREATE_TIME > to_date('2020-07-29 19:00:00','yyyy-mm-dd hh24:mi:ss');

example 5_1： Without milliseconds

 

example 5_2： belt 3 Bit milliseconds

example 5_3： other

select to_char(sysdate,'yyyy') as nowYear   from dual;   -- The year to get time   
select to_char(sysdate,'mm')    as nowMonth from dual;   -- Get the month of time   
select to_char(sysdate,'dd')    as nowDay    from dual;   -- Get the day of time   
select to_char(sysdate,'hh24') as nowHour   from dual;   -- The time to get time   
select to_char(sysdate,'mi')    as nowMinute from dual;   -- Get the minutes of time   
select to_char(sysdate,'ss')    as nowSecond from dual;   -- Get the seconds of time 

example 5_4： Query data

notes ：
although sysdate、systimestamp、to_date()、to_timestamp() Can be used to generate a date Type or timestamp type , But there will be some default gaps . So don't mix them up , As for the type of the field itself, use the function of the corresponding type to create a time value
    ⑴ Generate a date type ： Use sysdate or to_date()
    ⑵ Generate a timestamp type ： Use systimestamp or to_timestamp()
    ⑶ Will a date Type or timestamp The time value of type is converted to string type ： Use to_char(), It just means that you need to distinguish when specifying the format

 

 

Oracle Date addition and subtraction

Oracle There are many ways to add or subtract dates in , Here are three
    ⑴ One is the operation for days ： It is applicable to Japan , when , branch , Second operation
    ⑵ One is the operation of the month ： For month , Years of operation
    ⑶ One is to use INTERVAL function ： Applicable to , month , Japan , when , branch , Second operation

 

Add and subtract numbers directly

1、 The addition and subtraction of days are mainly in sysdate Go ahead directly on the day , when , branch , The addition and subtraction of seconds

2、Oracle Use in sysdate Function to get the current system time

Method	describe
SYSDATE	current time
SYSDATE+1	Add a day
SYSDATE+(1/24)	Add an hour
SYSDATE+(1/24/60)	One more minute
SYSDATE+(1/24/60/60)	Add one second
SYSDATE-1	One day less

example 6： Query data

example 6_1： insert data

 

adopt ADD_MONTHS() function

Method	describe
ADD_MONTHS(SYSDATE, 1)	Add a month
ADD_MONTHS(SYSDATE, -1)	Minus one month
ADD_MONTHS(SYSDATE, 1*12)	Add a year
ADD_MONTHS(SYSDATE, -1*12)	Minus one year

 

Use INTERVAL function

Method	describe
SYSDATE + INTERVAL '1' YEAR	Add a year
SYSDATE + INTERVAL '-1' YEAR	Minus one year
SYSDATE + INTERVAL '1' MONTH	Add a month
SYSDATE + INTERVAL '1' DAY	Add a day
SYSDATE + INTERVAL '1' HOUR	Add an hour
SYSDATE + INTERVAL '1' MINUTE	One more minute
SYSDATE + INTERVAL '1' SECOND	Add a second

                                        

trunc() function

explain ：Oracle Medium trunc() Function is used to intercept time type or number

grammar ：TRUNC(number,num_digits)

Parameters ：
    ⑴Number： A number or time that requires truncation
    ⑵Num_digits： Number used to specify rounding precision .Num_digits The default value of 0

notes ：
1、TRUNC() Function does not round when intercepting

2、to_char Function support date and timestamp, however trunc But I do not support TIMESTAMP data type

 

Processing date

TRUNC() The date processing method of the function is ： The intercepted part retains its value , The UN intercepted part is saved as 0

Method	describe
trunc(sysdate,'dd')	Return to the current date ( Accurate to the sky )
trunc(sysdate,'hh')	Returns the year, month, day and hour of the current time ( Accurate to the hour ）
trunc(sysdate,'mi')	Returns the time of the current time ( To the minute , There is no such thing as a second )
trunc(sysdate,'mm')	Back to the first day of the month
trunc(sysdate,'yy')	Back to the first day of the year
trunc(sysdate,'yyyy')	Back to the first day of the year
trunc(sysdate,'d')	Return to the first day of the current week ( Sunday )

example 7：dd

INSERT INTO USER_INFO(ID,NAME,CREATE_TIME,UPDATE_TIME) VALUES(5,' Xiaohong ',trunc(sysdate,'dd'),trunc(sysdate,'dd'));

-- Accurate to the sky , Then the time and second values are 0

example 7_1：

INSERT INTO USER_INFO(ID,NAME,CREATE_TIME,UPDATE_TIME) VALUES(6,' Xiao Ming ',trunc(sysdate,'hh'),trunc(sysdate,'hh'));

-- Accurate to the hour , Then the value of minutes and seconds is 0

example 7_2：sysdate You can also add or subtract time

-- After the intercept time , Add and subtract time 
INSERT INTO USER_INFO(ID,NAME,CREATE_TIME,UPDATE_TIME) VALUES(7,' Xiao Zhang ',(trunc(sysdate,'hh')+2/24),(trunc(sysdate,'hh')+30/24/60));

 

Processing values

1、TRUNC(n1, n2): Used to base on n2 Intercept n1 And return the result ,n2 Omission . Truncated values are not rounded

2、n2 Parameters can be positive or negative
    ⑴ A negative number means that it is truncated from the first digit to the left of the decimal point and then set to zero
    ⑵ A positive number means to keep one digit after the decimal point
    ⑶ Truncate the integral part ： Can not pass n2 Parameters can also be passed N2=0
    
example 8：

example 8_1：

 

 

expand

timestamp keyword

Oracle Can also be used in timestamp Keyword to convert a time string value to date type

example 9：

insert into USER_INFO (ID,NAME,COUNTRY,DATE_TIME,TIMESTAMP) values(4,' Li Liu ','China',timestamp '2020-07-30 20:30:30',timestamp '2020-07-30 20:30:30.55555')

 

Query database system time

SELECT SYSDATE FROM DUAL

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual​​​​​​​

--oracle We can't omit from keyword ,dual​​​​​​​ This watch is oracle My watch , So you can use