SQL Date Time Type processing

SQL date (Dates) 2019-10-17 22:17:26

When we deal with the date, it is probably the most difficult task to ensure that the date format is inserted, and format of the date column in the database matches.

If the date is part saved, the query will not be much problem. But if it comes to part time, the situation is a bit complicated.

Here we take a look at the built-in date processing function

SQL Server Date Functions

Here are the most important built-in date functions in SQL Server:

1, GETDATE () returns the current date and time

grammar:

GETDATE()

The following is a SELECT statement:

SELECT GETDATE() AS DateTime

The results are as follows:

NOTE: The above time to the millisecond.

2, DATEPART () Returns the separate portions of date / time

grammar:

DATEPART(datepart,date)

date parameter is valid date expression. datepart parameter may be a value of the following:

datepart	abbreviation
year	yy,yyyy
Quarter	qq,q
month	mm,m
On the day	house, the
day	dd,d
week	wk，ww
week	dw，w
hour	hh
minute	me n
second	ss，s
millisecond	ms
Microsecond	mcs
Ns	ns

Example:

select datepart(yy,getdate());

3, DATEADD () to add or subtract the date specified time interval

grammar:

DATEADD(datepart,number,date)

date parameter is valid date expression. number is the number of intervals you want to add; for a future date, the number is a positive number, for the last time, the number is negative.

Datepart parameter values consistent with the parameters listed above, and I will not copy the

Example:

select DATEADD(day,30,GETDATE());

result:

4, DATEDIFF () Returns the time between two dates

grammar:

DATEDIFF(datepart,startdate,enddate)

startdate argument is legitimate and enddate date expression. datepart parameters listed above like 

  examples:

select DATEDIFF(day,'2019-10-17','2020-1-24');

result:

5, CONVART () displays the date / time data in different formats

grammar:

CONVERT(data_type(length),expression,style)

value	description
data_type(length)	Predetermined target data type (with optional length).
express	Prescribed values need to be converted.
style	Predetermined date / time of the output format

The following table shows the style values datetime or smalldatetime conversion to character data:

Value (Century yy)	Value (Century yyyy)	input Output	standard
-	0 or 100	mon dd yyyy hh:miAM(or PM)	Default
1	101	mm/dd/yy	USA
2	102	yy.mm.dd	ANSI
3	103	dd/mm/yy	British/French
4	104	dd.mm.yy	German
5	105	dd-mm-yy	ltalian
6	106	dd mon yy
7	107	Mon dd,yy
8	108	hh:mm:ss
-	9 or 109	mon dd yyyy hh:mi:ss:mmmAM(or PM)	Default+millisec
10	110	mm-dd-yy	USA
11	111	yy/mm/dd	Japan
12	112	yymmdd	ISO
-	13 or 113	dd mon yyyy hh:mi:ss:mmm(24h)
14	114	hh:mi:ss:mmm(24h)
-	20 or 120	yyyy-mm-dd hh:mi:ss(24h)
-	21 or 121	yyyy-mm-dd hh:mi:ss.mmm(24h)
-	126	yyyy-mm-ddThh:mi:ss.mmm(no spaces)	ISO8601
-	130	dd mon yyyy hh:mi:ss:mmmAM	Hijiri
-	131	dd/mm/yy hh:mi:ss:mmmAM	Hijiri

Example:

The following script uses the CONVERT () function to display different formats. Use GETDATE () function to get the current date / time

CONVERT(VARCHAR(19),GETDATE())
CONVERT(VARCHAR(10),GETDATE(),10)
CONVERT(VARCHAR(10),GETDATE(),110)
CONVERT(VARCHAR(11),GETDATE(),6)
CONVERT(VARCHAR(11),GETDATE(),106)
CONVERT(VARCHAR(24),GETDATE(),113)

The results are as follows:

Nov 04  2011  11 : 45 PM
 11 - 04 - 11 
11 - 04 - 2011 
04 Nov 11 
04 Nov 2011 
04 Nov 2011  11 : 45 : 34 : 243

PostgreSQL time / date functions and operators

In certain postgre in time, the operator can perform basic number plus + subtraction - addition multiplication * / operation

Date / Time Operators

Operators	example	result
+	select date '2019-10-18' +integer '7'	date '2019-10-25'
+	select date '2019-10-18' + interval '1 hour'	timestamp '2019-10-18 01:00:00'
+	select date '2019-10-18' + time '03:00'	timestamp '2019-10-18 03:00:00'
+	select interval '1 day' + interval '1 hour'	interval '1 day 01:00:00'
+	select timestamp '2019-10-18 01:00' + interval '23 hours'	timestamp '2019-10-19 00:00:00'
+	select time '01:00' + interval '3 hours'	time '04:00:00'
-	- interval '23 hours'	interval -23:00:00
-	select date '2019-10-18' - date '2019-10-15'	intrger 3(days)
-	select date '2019-10-18' - integer '7'	date '2019-10-11'
-	date '2001-09-28' - interval '1 hour'	timestamp '2019-10-17 23:00:00'
-	time '05:00' - time '03:00'	interval '02:00:00'
-	time '05:00' - interval '2 hours'	time '03:00:00'
-	select timestamp '2019-10-18 23:00' - interval '23 hours'	timestamp '2019-10-18 00:00:00'
-	select interval '1 day' - interval '1 hour'	interval '1 day -01:00:00'
-	timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00'	interval '2 days 15:00:00'
*	900 * interval '1 second'	interval '00:15:00'
*	select 21 * interval '1 day'	interval '21 days'
*	select double precision '3.5' * interval '1 hour'	interval '03:30:00'
/	interval '1 hour' / double precision '1.5'	interval '00:40:00'

Date / Time Functions

function	Return Type	description	example	result
age(`timestamp`, `timestamp`)	interval	After subtracting the parameter "symbol" of the results, using the year and month, not just the use of space	select age(timestamp '2019-10-18', timestamp '1998-07-31')	"21 years 2 mons 18 days"
age(`timestamp`)	interval	从`current_date`减去参数后的结果（在午夜）	select age(timestamp '1998-07-31')	"21 years 2 mons 18 days"
clock_timestamp()	timestamp with time zone	实时时钟的当前时间戳（在语句执行时变化）	select clock_timestamp()	"2019-10-18 21:47:03.880667+08"
current_date	date	当前的日期；	select current_date	"2019-10-18"
current_time	time with time zone	当前的时间；	select current_time	"21:50:35.168911+08:00"
current_timestamp	timestamp with time zone	当前事务开始时的时间戳；	select current_timestamp	"2019-10-18 21:49:17.912353+08"
date_part(`text`, `timestamp`)	double precision	获取子域(等效于`extract`)；	date_part('hour', timestamp '2001-02-16 20:38:40')	22
date_part(`text`, `interval`)	double precision	获取子域(等效于`extract`)；	date_part('month', interval '2 years 3 months')	3
date_trunc(`text`, `timestamp`)	timestamp	截断成指定的精度；	select date_trunc('hour', timestamp '2019-10-18 22:55:40')	"2019-10-18 22:00:00"
date_trunc(`text`, `interval`)	interval	截取指定的精度，	date_trunc('hour', interval '2 days 3 hours 40 minutes')	"2 days 03:00:00"
`extract`(`field` from `timestamp`)	double precision	获取子域；	select extract(hour from timestamp '2019-10-18 22:58:40')	"22"
`extract`(`field` from `interval`)	double precision	获取子域；	select extract(month from interval '2 years 3 months')	"3"
isfinite(`date`)	boolean	测试是否为有穷日期(不是 +/-无穷)	select isfinite(date '2019-10-18')	true
isfinite(`timestamp`)	boolean	测试是否为有穷时间戳(不是 +/-无穷)	select isfinite(timestamp '2001-02-16 21:28:30')	true
isfinite(`interval`)	boolean	测试是否为有穷时间间隔	select isfinite(interval '4 hours')	true
justify_days(`interval`)	interval	按照每月 30 天调整时间间隔	select justify_days(interval '35 days')	"1 mon 5 days"
justify_hours(`interval`)	interval	按照每天 24 小时调整时间间隔	select justify_hours(interval '27 hours')	"1 day 03:00:00"
justify_interval(`interval`)	interval	使用`justify_days`和`justify_hours`调整时间间隔的同时进行正负号调整	select justify_interval(interval '1 mon -1 hour')	"29 days 23:00:00"
localtime	time	当日时间；	select localtime	"22:29:47.906458"
localtimestamp	timestamp	当前事务开始时的时间戳；	select localtimestamp	"2019-10-18 22:30:51.573436"
make_date(`year` `int`, `month` `int`, `day` `int`)	date	为年、月和日字段创建日期	make_date(2013, 7, 15)	2013-07-15
now()	timestamp with time zone	当前事务开始时的时间戳；	select now()	"2019-10-18 22:33:19.559465+08"
statement_timestamp()	timestamp with time zone	实时时钟的当前时间戳；	statement_timestamp()	"2019-10-18 22:34:50.077578+08"
timeofday()	text	与`clock_timestamp`相同，但结果是一个`text` 字符串；	select timeofday()	"Fri Oct 18 22:35:41.196317 2019 HKT"
transaction_timestamp()	timestamp with time zone	当前事务开始时的时间戳；	select transaction_timestamp()	"2019-10-18 22:36:42.310184+08"

SQL Date Time Type processing

Guess you like