Tuesday, January 27, 2015

Chuyển đổi giữa String và Date trong SQL .

Execute the following Microsoft SQL Server T-SQL scripts in Management Studio Query Editor to demonstrate the conversion from string to date (DATE, DATETIME, SMALLDATETIME).
When a conversion involves month or day name, it is language setting dependent, therefore non-deterministic. The week function is also non-deterministic because it depends on the first date setting for the week (default in sys.syslanguages table or override by SET DATEFIRST).
USE AdventureWorks
SET LANGUAGE us_english
-- Convert string to date using style (format) numbers - sql dates format
-- SQL convert text to date - SQL convert string to date / datetime
SELECT convert(datetime,'15/03/18',3) -- 2018-03-15 00:00:00.000
SELECT convert(datetime,'15.03.18',4) -- 2018-03-15 00:00:00.000

-- Convert datetime to text style (format) list - sql time format
-- SQL Server without century (YY) date styles (there are exceptions!)
-- Generally adding 100 to style number results in century format CCYY / YYYY
SELECT convert(varchar,getdate())    -- Mar 15 2018 10:35AM
SELECT convert(varchar,getdate(),0)  -- Mar 15 2018 10:35AM
SELECT convert(varchar,getdate(),1)  -- 03/15/18
SELECT convert(varchar,getdate(),2)  -- 18.03.15
SELECT convert(varchar,getdate(),3)  -- 15/03/18
SELECT convert(varchar,getdate(),4)  -- 15.03.18
SELECT convert(varchar,getdate(),5)  -- 15-03-18
SELECT convert(varchar,getdate(),6)  -- 15 Mar 18
SELECT convert(varchar,getdate(),7)  -- Mar 15, 18
SELECT convert(varchar,getdate(),8)  -- 10:39:39
SELECT convert(varchar,getdate(),9)  -- Mar 15 2018 10:39:48:373AM
SELECT convert(varchar,getdate(),10) -- 03-15-18
SELECT convert(varchar,getdate(),11) -- 18/03/15
SELECT convert(varchar,getdate(),15) -- 180315
SELECT convert(varchar,getdate(),13) -- 15 Mar 2018 10:41:07:590
SELECT convert(varchar,getdate(),14) -- 10:41:25:903
SELECT convert(varchar,getdate(),20) -- 2018-03-15 10:43:56
SELECT convert(varchar,getdate(),21) -- 2018-03-15 10:44:04.950
SELECT convert(varchar,getdate(),22) -- 03/15/18 10:44:50 AM
SELECT convert(varchar,getdate(),23) -- 2018-03-15
SELECT convert(varchar,getdate(),24) -- 10:45:45
SELECT convert(varchar,getdate(),25) -- 2018-03-15 10:46:11.263

-- T-SQL with century (YYYY or CCYY) datetime styles (formats)

SELECT convert(varchar, getdate(), 100) -- Oct 23 2016 10:22AM (or PM)
SELECT convert(varchar, getdate(), 101) -- 10/23/2016
SELECT convert(varchar, getdate(), 102) -- 2016.10.23
SELECT convert(varchar, getdate(), 103) -- 23/10/2016
SELECT convert(varchar, getdate(), 104) -- 23.10.2016
SELECT convert(varchar, getdate(), 105) -- 23-10-2016
SELECT convert(varchar, getdate(), 106) -- 23 Oct 2016
SELECT convert(varchar, getdate(), 107) -- Oct 23, 2016
SELECT convert(varchar, getdate(), 108) -- 09:10:34
SELECT convert(varchar, getdate(), 109) -- Oct 23 2016 11:10:33:993AM (or PM)
SELECT convert(varchar, getdate(), 110) -- 10-23-2016
SELECT convert(varchar, getdate(), 111) -- 2016/10/23
SELECT convert(varchar, getdate(), 112) -- 20161023
SELECT convert(varchar, getdate(), 113) -- 23 Oct 2016 06:10:55:383
SELECT convert(varchar, getdate(), 114) -- 06:10:55:383(24h)
SELECT convert(varchar, getdate(), 120) -- 2016-10-23 06:10:55(24h)
SELECT convert(varchar, getdate(), 121) -- 2016-10-23 06:10:55.383
SELECT convert(varchar, getdate(), 126) -- 2016-10-23T06:10:55.383
GO
-- SQL cast string to datetime - time part 0 - sql hh mm
-- SQL Server cast string to DATE (SQL Server 2008 feature) - sql yyyy mm dd
SELECT [Date] =     CAST('20120228' AS date)         -- 2012-02-28
SELECT [Datetime] = CAST('20120228' AS datetime)      -- 2012-02-28 00:00:00.000
SELECT [Datetime] = CAST('20120228' AS smalldatetime) -- 2012-02-28 00:00:00

-- SQL convert string to datetime - time part 0
-- SQL Server convert string to date - sql times format
SELECT [Datetime] = CONVERT(datetime,'2010-02-28')
SELECT [Datetime] = CONVERT(smalldatetime,'2010-02-28')

SELECT [Datetime] = CAST('Mar 15, 2010' AS datetime)
SELECT [Datetime] = CAST('Mar 15, 2010' AS smalldatetime)

SELECT [Datetime] = CONVERT(datetime,'Mar 15, 2010')
SELECT [Datetime] = CONVERT(smalldatetime,'Mar 15, 2010')

SELECT [Datetime] = CAST('Mar 15, 2010 12:07:34.444' AS datetime)
SELECT [Datetime] = CAST('Mar 15, 2010 12:07:34.444' AS smalldatetime)

SELECT [Datetime] = CONVERT(datetime,'Mar 15, 2010 12:07:34.444')
SELECT [Datetime] = CONVERT(smalldatetime,'Mar 15, 2010 12:07:34.444')

SELECT [Datetime] = CAST('2010-02-28 12:07:34.444' AS datetime)
SELECT [Datetime] = CAST('2010-02-28 12:07:34.444' AS smalldatetime)

SELECT [Datetime] = CONVERT(datetime,'2010-02-28 12:07:34.444')
SELECT [Datetime] = CONVERT(smalldatetime,'2010-02-28 12:07:34.444')

-- Double conversion
SELECT [Datetime] = CAST(CAST(getdate() AS VARCHAR) AS datetime)
SELECT [Datetime] = CAST(CAST(getdate() AS VARCHAR) AS smalldatetime)

SELECT [Datetime] = CONVERT(datetime,convert(varchar,getdate()))
SELECT [Datetime] = CONVERT(smalldatetime,convert(varchar,getdate()))
------------

-- MSSQL convert date string to datetime - time is set to 00:00:00.000 or 12:00AM
PRINT CONVERT(datetime,'07-10-2016',110)        -- Jul 10 2016 12:00AM
PRINT CONVERT(datetime,'2016/07/10',111)        -- Jul 10 2016 12:00AM
PRINT CONVERT(varchar,CONVERT(datetime,'20160710',  112),121)          
-- 2016-07-10 00:00:00.000        
------------     

-- Selected named date styles
DECLARE @DateTimeValue varchar(32)

-- US-Style
-- Convert string to datetime sql - sql convert string to datetime
SELECT @DateTimeValue = '10/23/2016'
SELECT StringDate=@DateTimeValue,
[US-Style] = CONVERT(datetime, @DatetimeValue)

SELECT @DateTimeValue = '10/23/2016 23:01:05'
SELECT StringDate = @DateTimeValue,
[US-Style] = CONVERT(datetime, @DatetimeValue)

-- UK-Style, British/French
SELECT @DateTimeValue = '23/10/16 23:01:05'
SELECT StringDate = @DateTimeValue,
[UK-Style] = CONVERT(datetime, @DatetimeValue, 3)

SELECT @DateTimeValue = '23/10/2016 04:01 PM'
SELECT StringDate = @DateTimeValue,
[UK-Style] = CONVERT(datetime, @DatetimeValue, 103)

-- German-Style
SELECT @DateTimeValue = '23.10.16 23:01:05'
SELECT StringDate = @DateTimeValue,
[German-Style] = CONVERT(datetime, @DatetimeValue, 4)


SELECT @DateTimeValue = '23.10.2016 04:01 PM'
SELECT StringDate = @DateTimeValue,
[German-Style] = CONVERT(datetime, @DatetimeValue, 104)


-- Double conversion to US-Style 107 with century: Oct 23, 2016
SET @DateTimeValue='10/23/16'
SELECT StringDate=@DateTimeValue,
[US-Style] = CONVERT(varchar, CONVERT(datetime, @DateTimeValue),107)

-- SQL dateformat setting
USE AdventureWorks2008;
SELECT convert(datetime,'14/05/08')
/* Msg 242, Level 16, State 3, Line 1
The conversion of a varchar data type to a datetime data type resulted
in an out-of-range value.
*/
SET DATEFORMAT ymd
SELECT convert(datetime,'14/05/08')   -- 2014-05-08 00:00:00.000
-- Setting DATEFORMAT to UK-Style
SET DATEFORMAT dmy
SELECT convert(datetime,'20/05/14')   -- 2014-05-20 00:00:00.000
-- Setting DATEFORMAT to US-Style
SET DATEFORMAT mdy
SELECT convert(datetime,'05/20/14')   -- 2014-05-20 00:00:00.000
SELECT convert(datetime,'05/20/2014') -- 2014-05-20 00:00:00.000
GO

------------
-- SQL date & time eliminating dividing characters
------------
-- MSSQL replace string function
-- T-SQL string concatenate (+)
USE AdventureWorks2008;
SELECT replace(convert(VARCHAR(10),getdate(),102),'.','')
-- 20120315
SELECT replace(convert(VARCHAR(10),getdate(),111),'/','')
-- 20120315  
-- SQL triple replace
SELECT replace(replace(replace(convert(VARCHAR(25),
       getdate(),20),'-',''), ':',''),' ','')
-- 20120529090427
-- T-SQL concatenating from a date and a time conversion
SELECT replace(convert(VARCHAR(10),getdate(),111),'/','') +
       replace(convert(VARCHAR(8),getdate(),108),':','')
-- 20120315085654

------------
-- Converting string dates from a table
------------

-- Create and populate a test table with a string date
USE tempdb;
SELECT
      DepartmentID,
      LastUpdate=CONVERT(varchar,
                 dateadd(day, DepartmentID, ModifiedDate),100)
INTO DeptInfo
FROM AdventureWorks.HumanResources.Department

SELECT * FROM DeptInfo
/* Partial results

DepartmentID      LastUpdate
1                       Jun  2 1998 12:00AM
2                       Jun  3 1998 12:00AM
*/

-- Convert string date column to datetime
SELECT
      DepartmentID,
      LastChangeDate=convert(datetime, LastUpdate)
FROM DeptInfo
/* Partial results

DepartmentID            LastChangeDate
1                       1998-06-02 00:00:00.000
2                       1998-06-03 00:00:00.000
*/
DROP TABLE DeptInfo
GO

The BEST 70-461 SQL Server 2012 Querying Exam Prep Book!
-------------------------------------------------------
-- Casting string date & time together and separately
-------------------------------------------------------
-- SQL cast string to datetime
SELECT CAST('20100315 16:40:31' AS datetime)
-- Result: 2010-03-15 16:40:31.000

-- SQL cast string to date - time part 0  
SELECT CAST('20100315' AS datetime)
-- Result: 2010-03-15 00:00:00.000

-- SQL cast string to time - date part 1900-01-01
SELECT CAST('16:40:31' AS smalldatetime)
-- Result: 1900-01-01 16:41:00
------------
-- SQL DATEDIFF with string date
------------
DECLARE @sDate varchar(10)
SET @sDate = '2010/03/15'
-- DATEDIFF (delta) between two dates in months
SELECT GETDATE(), DATEDIFF (MONTH, GETDATE(), @sDate)
SELECT GETDATE(), DATEDIFF (MONTH, GETDATE(), CAST(@sDate as datetime))
SELECT GETDATE(), DATEDIFF (MONTH, GETDATE(), CONVERT(datetime,@sDate))
SELECT GETDATE(), DATEDIFF (MONTH, GETDATE(), CONVERT(datetime,@sDate,111))
-- Seme results for above: 2008-12-29 11:04:51.097    15

-- SQL convert to datetime with wrong style (111 correct, 112 incorrect)
SELECT GETDATE(), DATEDIFF (MONTH, GETDATE(), CONVERT(datetime,@sDate,112))
/* ERROR

Msg 241, Level 16, State 1, Line 11
Conversion failed when converting date and/or time from character string.
*/
------------
------------
-- SQL Server date string search guidelines - comparing dates
------------
-- Date equal search
DECLARE @Date1 datetime, @Date2 datetime, @Date3 datetime
SET @Date1 = '2012-01-01'
SET @Date2 = '2012-01-01 00:00:00.000'
SET @Date3 = '2012-01-01 11:00'

SELECT @Date1, @Date2, @Date3
-- Date-only @Date1 is translated to datetime
-- 2012-01-01 00:00:00.000    2012-01-01 00:00:00.000  2012-01-01 11:00:00.000

-- The following is a datetime comparison, not a date-only comparison
IF (@Date1 = @Date2) PRINT 'EQUAL' ELSE PRINT 'NOT EQUAL'
-- EQUAL

-- Equal test fails because time parts are different
IF (@Date1 = @Date3) PRINT 'EQUAL' ELSE PRINT 'NOT EQUAL'
-- NOT EQUAL
-- The string date implicitly converted to datetime for the equal test
IF ('2012-01-01' = @Date3) PRINT 'EQUAL' ELSE PRINT 'NOT EQUAL'
-- NOT EQUAL

-- Safe way to search for a specific date
SELECT COUNT(*) FROM AdventureWorks.Sales.SalesOrderHeader
WHERE '2004/02/01' = CONVERT(varchar, OrderDate,111)
-- 244

-- Equivalent to
SELECT COUNT(*) FROM AdventureWorks.Sales.SalesOrderHeader
WHERE OrderDate BETWEEN '2004/02/01  00:00:00.000' AND '2004/02/01 23:59:59.997'
-- 244


-- Safe way to search for a specific date range
SELECT COUNT(*) FROM AdventureWorks.Sales.SalesOrderHeader
WHERE CONVERT(varchar, OrderDate,111) BETWEEN '2004/02/01' AND '2004/02/14'
-- 1059

-- Equivalent to
SELECT COUNT(*) FROM AdventureWorks.Sales.SalesOrderHeader
WHERE OrderDate BETWEEN '2004/02/01 00:00:00.000' AND '2004/02/14 23:59:59.997'
-- 1059
SELECT COUNT(*) FROM AdventureWorks.Sales.SalesOrderHeader
WHERE OrderDate >= '2004/02/01 00:00:00.000'
  AND OrderDate <  '2004/02/15 00:00:00.000'
-- 1059 
------------
------------
-- SQL Server convert from string to smalldatetime
------------
-- T-SQL convert from format mm/dd/yyyy to smalldatetime
SELECT CONVERT(smalldatetime, '10/23/2016', 101)
-- 2016-10-23 00:00:00
-- MSSQL convert from format dd/mm/yyyy to smalldatetime
SELECT CONVERT(smalldatetime, '23/10/2016', 103)
-- 2016-10-23 00:00:00
-- Month 23 is out of range
SELECT CONVERT(smalldatetime, '23/10/2016', 101)
/* Msg 242, Level 16, State 3, Line 1
The conversion of a varchar data type to a smalldatetime data type resulted
in an out-of-range value.
*/
------------
-- Translate/convert string/text hours and minutes to seconds
------------
DECLARE @TimeStr varchar(16) = '20:49:30'
SELECT   PARSENAME(REPLACE(@TimeStr,':','.'),1)
       + PARSENAME(REPLACE(@TimeStr,':','.'),2) * 60
       + PARSENAME(REPLACE(@TimeStr,':','.'),3) * 3600
-- 74970
------------

Source : sqlusa

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