I have a query like :
SELECT ..
FROM ...
WHERE ...
AND ISNULL(ICA.actual_appearance_date, ICA.scheduled_appearance_date)
BETWEEN LO.order_start_date
AND ISNULL(LO.actual_expiry_date, LO.expected_expiry_date)
Is there a neat way to only check that the actual_appearance_date is between the start and end date, but not include time?
So:
Appearance Date is 03/Oct/2011 # 14h00... and the dates we're check are 03/Oct/2011 # 15h00 and and 07/Oct/2011 # 10h00.
At the moment, that would not yield a result because of the time factors. I need to do a between on the date part only... So, between 03/Oct/2011 # 0h00 and really 08/Oct/2011 # 0:00.
Is there a neat way to do this?
Edit:
We're developing for a 2008 machine, but we're developing ON 2005 machines. Long story, but I can't use the nice and neat DATE fix.
I am trying the DATEADD method, but am finding an issue.
This is not returning the result I expect:
DECLARE #Table TABLE
(
StartDate DATETIME,
EndDate DATETIME
)
INSERT INTO #Table VALUES ('02-Jan-2011 13:00:00', '07-Jan-2011 15:30:00')
SELECT * FROM #Table
DECLARE #Date DATETIME
SET #Date = '07-Jan-2011 16:00:00'
SELECT
CASE WHEN
#Date BETWEEN DATEADD(dd,DATEDIFF(dd,0,StartDate),0) AND DATEADD(dd, DATEDIFF(dd,0,EndDate),0)-- must cover the appearance date or still open
THEN 1
ELSE 0
END AS Result
FROM #Table
Must I add +1 to the BETWEEN dates to include the last date? 'BETWEEN' doesn't seem to be inclusive of the last date..
You have SQL Server 2008 so just cast to date
SELECT ..
FROM ...
WHERE ... AND
CAST(ISNULL(ICA.actual_appearance_date, ICA.scheduled_appearance_date) AS date)
BETWEEN
CAST(LO.order_start_date AS date)
AND
CAST(ISNULL(LO.actual_expiry_date, LO.expected_expiry_date) AS date)
For SQL Server 2005 and earlier, use the DATEDIFF/DATEADD trick: Best approach to remove time part of datetime in SQL Server
Do not use varchar or float conversions
Edit:, for SQL Server 2005
You need to apply the DATEADD/DATEDIFF to all values
...
SELECT
CASE WHEN
DATEADD(dd,DATEDIFF(dd,0,#Date),0)
BETWEEN DATEADD(dd,DATEDIFF(dd,0,StartDate),0)
AND DATEADD(dd, DATEDIFF(dd,0,EndDate),0)
THEN 1
ELSE 0
END AS Result
FROM #Table
Or
WHERE ... AND
DATEADD(dd,DATEDIFF(dd,0,ISNULL(ICA.actual_appearance_date, ICA.scheduled_appearance_date),0)
BETWEEN
DATEADD(dd,DATEDIFF(dd,0,LO.order_start_date),0)
AND
DATEADD(dd,DATEDIFF(dd,0,ISNULL(LO.actual_expiry_date, LO.expected_expiry_date),0)
You can use the convert process then compare:
Convert(Datetime,Convert(Varchar,OrderDate,106),110)
Related
I am trying to convert a string into DateTimeOffset (in SQL Server) through a ETL job. Basically, my string would look something like '2017-10-15' and I want this to be converted into a DatetimeOffset (from the current DB server).
SELECT
SWITCHOFFSET(DATEADD(mi, DATEDIFF(MI, GETDATE(), GETUTCDATE()), CAST(#DateInString + ' 00:00:00' AS DATETIMEOFFSET)), DATENAME(tzoffset, SYSDATETIMEOFFSET()))
I have been getting some weird issues with this statement as the final output would fall either +1 / -1 minute than the expected ones. This happens for at least every 10 records/million. I tried to nail down the issue and I could see the problem was with the DATEDIFF() method returning +/-1 minute.
SELECT DATEDIFF(MI, GETDATE(), GETUTCDATE())
This should exactly return -600 (since my DB server UTC is +10). However, it returns either -599 or 601 for few records. I execute them as a single select statement in my Stored Procedure and return it as a parameter.
This is weird on how SQL could detect two different datetime values for GETDATE() and GETUTCDATE() on the same select statement.
Is there a way to force SQL to get exactly same dates in those DATEDIFF parameters or am I missing something here? Thanks in advance
I am using SQL Server 2014 (v12.0).
Stored procedure:
CREATE PROCEDURE dbo.SPConvertDateTimeOffset
#DateInString VARCHAR(10),
#DateTimeOffset_Value DATETIMEOFFSET OUTPUT,
#Datediff_Value INT OUTPUT
AS
BEGIN
-- This line returns +/- 1
SELECT #Datediff_Value = DATEDIFF(MI, GETDATE(), GETUTCDATE())
SELECT #DateTimeOffset_Value = SWITCHOFFSET(DATEADD(mi, #Datediff_Value, CAST(#DateInString + ' 00:00:00' AS DATETIMEOFFSET)), DATENAME(tzoffset, SYSDATETIMEOFFSET()))
END
#GordonLinoff has explained why this happens: since functions are executed at slightly different times, they may return a different minute.
To work around, try this:
DECLARE #DateTimeOffset_Value Datetimeoffset
DECLARE #Datediff_Value INT, #DateInString VARCHAR( 10 )
SET #DateInString = CONVERT( VARCHAR, GETDATE(), 112 )
SET #DateTimeOffset_Value = TODATETIMEOFFSET( #DateInString, DATENAME(tzoffset,SYSDATETIMEOFFSET()))
SET #Datediff_Value = DATEDIFF( MI, #DateInString, #DateTimeOffset_Value )
SELECT #DateInString, #DateTimeOffset_Value, #Datediff_Value
It does not use current date comparisons.
Note: that during the time when day light saving changes you may get a different value from the expected, depending on when exactly the code was run.
Have a look at https://dba.stackexchange.com/questions/28187/how-can-i-get-the-correct-offset-between-utc-and-local-times-for-a-date-that-is for more solutions about how to handle DTS changes.
The two functions are not executed simultaneously. So about 1 time in 100,000 (in your test) the times are on opposite sides of a minute boundary.
If you just want the timezone, you could try:
select datepart(tz, SYSDATETIMEOFFSET())
How would I be able to extract the time part of a DateTime field in SQL? For my project I have to return data that has a timestamp of 5pm of a DateTime field no matter what the date is
This will return the time-Only
For SQL Server:
SELECT convert(varchar(8), getdate(), 108)
Explanation:
getDate() is giving current date and time.
108 is formatting/giving us the required portion i.e time in this case.
varchar(8) gives us the number of characters from that portion.
Like:
If you wrote varchar(7) there, it will give you 00:00:0
If you wrote varchar(6) there, it will give you 00:00:
If you wrote varchar(15) there, it will still give you 00:00:00 because it is giving output of just time portion.
SQLFiddle Demo
For MySQL:
SELECT DATE_FORMAT(NOW(), '%H:%i:%s')
SQLFiddle Demo
In SQL Server if you need only the hh:mi, you can use:
DECLARE #datetime datetime
SELECT #datetime = GETDATE()
SELECT RIGHT('0'+CAST(DATEPART(hour, #datetime) as varchar(2)),2) + ':' +
RIGHT('0'+CAST(DATEPART(minute, #datetime)as varchar(2)),2)
If you want only the hour of your datetime, then you can use DATEPART() - SQL Server:
declare #dt datetime
set #dt = '2012-09-10 08:25:53'
select datepart(hour, #dt) -- returns 8
In SQL Server 2008+ you can CAST() as time:
declare #dt datetime
set #dt = '2012-09-10 08:25:53'
select CAST(#dt as time) -- returns 08:25:53
I know this is an old question, but since the other answers all
return strings (rather than datetimes),
rely on the internal representation of dates (conversion to float, int, and back) or
require SQL Server 2008 or beyond,
I thought I'd add a "pure" option which only requires datetime operations and works with SQL Server 2005+:
SELECT DATEADD(dd, -DATEDIFF(dd, 0, mydatetime), mydatetime)
This calculates the difference (in whole days) between date zero (1900-01-01) and the given date and then subtracts that number of days from the given date, thereby setting its date component to zero.
Try this in SQL Server 2008:
select *
from some_table t
where convert(time,t.some_datetime_column) = '5pm'
If you want take a random datetime value and adjust it so the time component is 5pm, then in SQL Server 2008 there are a number of ways. First you need start-of-day (e.g., 2011-09-30 00:00:00.000).
One technique that works for all versions of Microsoft SQL Server as well as all versions of Sybase is to use convert/3 to convert the datetime value to a varchar that lacks a time component and then back into a datetime value:
select convert(datetime,convert(varchar,current_timestamp,112),112)
The above gives you start-of-day for the current day.
In SQL Server 2008, though, you can say something like this:
select start_of_day = t.some_datetime_column
- convert(time, t.some_datetime_column ) ,
from some_table t
which is likely faster.
Once you have start-of-day, getting to 5pm is easy. Just add 17 hours to your start-of-day value:
select five_pm = dateadd(hour,17, t.some_datetime_column
- convert(time,t.some_datetime_column)
)
from some_table t
Note that from MS SQL 2012 onwards you can use FORMAT(value,'format')
e.g. WHERE FORMAT(YourDatetime,'HH:mm') = '17:00'
"For my project, I have to return data that has a timestamp of 5pm of a DateTime field, No matter what the date is."
So I think what you meant was that you needed the date, not the time. You can do something like this to get a date with 5:00 as the time:
SELECT CONVERT(VARCHAR(10), GetDate(), 110) + ' 05:00:00'
This should strip away the date part:
select convert(datetime,convert(float, getdate()) - convert(int,getdate())), getdate()
and return a datetime with a default date of 1900-01-01.
you can use CONVERT(TIME,GETDATE()) in this case:
INSERT INTO infoTbl
(itDate, itTime)
VALUES (GETDATE(),CONVERT(TIME,GETDATE()))
or if you want print it or return that time use like this:
DECLARE #dt TIME
SET #dt = CONVERT(TIME,GETDATE())
PRINT #dt
select cast(getdate() as time(0))
returns for example :- 15:19:43
replace getdate() with the date time you want to extract just time from!
SELECT DISTINCT
CONVERT(VARCHAR(17), A.SOURCE_DEPARTURE_TIME, 108)
FROM
CONSOLIDATED_LIST AS A
WHERE
CONVERT(VARCHAR(17), A.SOURCE_DEPARTURE_TIME, 108) BETWEEN '15:00:00' AND '15:45:00'
declare #datetime as datetime
set #datetime = getdate()
select cast(cast(#datetime as time) as varchar(8))
For year:
SELECT DATEPART(YEAR, '2021-03-21' );
For hour:
SELECT DATEPART(HOUR, '2021-03-21 08:50:30' );
Ii have values stored in the SQL Server in the following manner : 02-Jul-12 12:00:00 AM here the time and minutes, seconds can be anything like 02-Jul-12 12:15:52 PM ,02-Jul-12 6:02:12 AM so on.
I want to have a where condition which will omit the time and take the data based on the date like the following where some_Date='02-Jul-12'
How would I do this?
SELECT * FROM whatever WHERE some_Date LIKE '02-Jul-12%';
If you are on SQL2008 or later, you can cast your DATETIME to DATE.
See this post: http://blog.sqlauthority.com/2012/09/12/sql-server-get-date-and-time-from-current-datetime-sql-in-sixty-seconds-025-video/
But in a WHERE-clause it is better to search between dates, like this:
DECLARE #startDate DATETIME = '02-Jul-2012'
DECLARE #endDate DATETIME = DATEADD(DAY, 1, #startDate)
SELECT * FROM [table] WHERE [some_Date] BETWEEN #startDate AND #endDate
SELECT * FROM dbo.tbl_MyTable
WHERE
REPLACE(CONVERT(VARCHAR(9), DateTimeValueColumn, 6), ' ', '-')='02-Jul-12'
or
On chage in code is instead of using getdate function voncert you datestring in datetime format and do compare this follow query will work for you
SELECT * FROM dbo.tbl_MyTable
WHERE
CAST(CONVERT(CHAR(10), DateTimeValueColumn, 102) AS DATE) =
CAST(CONVERT(CHAR(10),GETDATE(),102) AS DATE)
If you are storing dates as characters -- which is not recommended -- you should at least use ISO format: YYYY-MM-DD hh:mm:ss. This makes the date useful for sorting and comparisons ("<" works, ">" works, "between" works as well as equals).
To extract the date, you can then use left(datestr, 10). In your format, you would use:
where left(datestr, 9) = '01-Jan-13'
If you are storing the fields as a datetime or smalldatetime, you may think they are stored as a string. They are not. They are stored as some number of days since some particular date, with day parts stored as fractional days. If you are using SQL Server 2005 or greater, then the best way is:
where cast(datetime as date) = '2013-01-01' -- I recommend ISO formats, even for constants. '20130101' is even better
To select rows with today's date (not time)
select * from myTable where datediff(dd, dateColumn, getdate()) = 0
How would I be able to extract the time part of a DateTime field in SQL? For my project I have to return data that has a timestamp of 5pm of a DateTime field no matter what the date is
This will return the time-Only
For SQL Server:
SELECT convert(varchar(8), getdate(), 108)
Explanation:
getDate() is giving current date and time.
108 is formatting/giving us the required portion i.e time in this case.
varchar(8) gives us the number of characters from that portion.
Like:
If you wrote varchar(7) there, it will give you 00:00:0
If you wrote varchar(6) there, it will give you 00:00:
If you wrote varchar(15) there, it will still give you 00:00:00 because it is giving output of just time portion.
SQLFiddle Demo
For MySQL:
SELECT DATE_FORMAT(NOW(), '%H:%i:%s')
SQLFiddle Demo
In SQL Server if you need only the hh:mi, you can use:
DECLARE #datetime datetime
SELECT #datetime = GETDATE()
SELECT RIGHT('0'+CAST(DATEPART(hour, #datetime) as varchar(2)),2) + ':' +
RIGHT('0'+CAST(DATEPART(minute, #datetime)as varchar(2)),2)
If you want only the hour of your datetime, then you can use DATEPART() - SQL Server:
declare #dt datetime
set #dt = '2012-09-10 08:25:53'
select datepart(hour, #dt) -- returns 8
In SQL Server 2008+ you can CAST() as time:
declare #dt datetime
set #dt = '2012-09-10 08:25:53'
select CAST(#dt as time) -- returns 08:25:53
I know this is an old question, but since the other answers all
return strings (rather than datetimes),
rely on the internal representation of dates (conversion to float, int, and back) or
require SQL Server 2008 or beyond,
I thought I'd add a "pure" option which only requires datetime operations and works with SQL Server 2005+:
SELECT DATEADD(dd, -DATEDIFF(dd, 0, mydatetime), mydatetime)
This calculates the difference (in whole days) between date zero (1900-01-01) and the given date and then subtracts that number of days from the given date, thereby setting its date component to zero.
Try this in SQL Server 2008:
select *
from some_table t
where convert(time,t.some_datetime_column) = '5pm'
If you want take a random datetime value and adjust it so the time component is 5pm, then in SQL Server 2008 there are a number of ways. First you need start-of-day (e.g., 2011-09-30 00:00:00.000).
One technique that works for all versions of Microsoft SQL Server as well as all versions of Sybase is to use convert/3 to convert the datetime value to a varchar that lacks a time component and then back into a datetime value:
select convert(datetime,convert(varchar,current_timestamp,112),112)
The above gives you start-of-day for the current day.
In SQL Server 2008, though, you can say something like this:
select start_of_day = t.some_datetime_column
- convert(time, t.some_datetime_column ) ,
from some_table t
which is likely faster.
Once you have start-of-day, getting to 5pm is easy. Just add 17 hours to your start-of-day value:
select five_pm = dateadd(hour,17, t.some_datetime_column
- convert(time,t.some_datetime_column)
)
from some_table t
Note that from MS SQL 2012 onwards you can use FORMAT(value,'format')
e.g. WHERE FORMAT(YourDatetime,'HH:mm') = '17:00'
"For my project, I have to return data that has a timestamp of 5pm of a DateTime field, No matter what the date is."
So I think what you meant was that you needed the date, not the time. You can do something like this to get a date with 5:00 as the time:
SELECT CONVERT(VARCHAR(10), GetDate(), 110) + ' 05:00:00'
This should strip away the date part:
select convert(datetime,convert(float, getdate()) - convert(int,getdate())), getdate()
and return a datetime with a default date of 1900-01-01.
you can use CONVERT(TIME,GETDATE()) in this case:
INSERT INTO infoTbl
(itDate, itTime)
VALUES (GETDATE(),CONVERT(TIME,GETDATE()))
or if you want print it or return that time use like this:
DECLARE #dt TIME
SET #dt = CONVERT(TIME,GETDATE())
PRINT #dt
select cast(getdate() as time(0))
returns for example :- 15:19:43
replace getdate() with the date time you want to extract just time from!
SELECT DISTINCT
CONVERT(VARCHAR(17), A.SOURCE_DEPARTURE_TIME, 108)
FROM
CONSOLIDATED_LIST AS A
WHERE
CONVERT(VARCHAR(17), A.SOURCE_DEPARTURE_TIME, 108) BETWEEN '15:00:00' AND '15:45:00'
declare #datetime as datetime
set #datetime = getdate()
select cast(cast(#datetime as time) as varchar(8))
For year:
SELECT DATEPART(YEAR, '2021-03-21' );
For hour:
SELECT DATEPART(HOUR, '2021-03-21 08:50:30' );
I'm trying to compare time in a datetime field in a SQL query, but I don't know if it's right. I don't want to compare the date part, just the time part.
I'm doing this:
SELECT timeEvent
FROM tbEvents
WHERE convert(datetime, startHour, 8) >= convert(datetime, #startHour, 8)
Is it correct?
I'm asking this because I need to know if 08:00:00 is less or greater than 07:30:00 and I don't want to compare the date, just the time part.
Thanks!
Your compare will work, but it will be slow because the dates are converted to a string for each row. To efficiently compare two time parts, try:
declare #first datetime
set #first = '2009-04-30 19:47:16.123'
declare #second datetime
set #second = '2009-04-10 19:47:16.123'
select (cast(#first as float) - floor(cast(#first as float))) -
(cast(#second as float) - floor(cast(#second as float)))
as Difference
Long explanation: a date in SQL server is stored as a floating point number. The digits before the decimal point represent the date. The digits after the decimal point represent the time.
So here's an example date:
declare #mydate datetime
set #mydate = '2009-04-30 19:47:16.123'
Let's convert it to a float:
declare #myfloat float
set #myfloat = cast(#mydate as float)
select #myfloat
-- Shows 39931,8244921682
Now take the part after the comma character, i.e. the time:
set #myfloat = #myfloat - floor(#myfloat)
select #myfloat
-- Shows 0,824492168212601
Convert it back to a datetime:
declare #mytime datetime
set #mytime = convert(datetime,#myfloat)
select #mytime
-- Shows 1900-01-01 19:47:16.123
The 1900-01-01 is just the "zero" date; you can display the time part with convert, specifying for example format 108, which is just the time:
select convert(varchar(32),#mytime,108)
-- Shows 19:47:16
Conversions between datetime and float are pretty fast, because they're basically stored in the same way.
convert(varchar(5), thedate, 108) between #leftTime and #rightTime
Explanation:
if you have varchar(5) you will obtain HH:mm
if you have varchar(8) you obtain HH:mm ss
108 obtains only the time from the SQL date
#leftTime and #rightTime are two variables to compare
If you're using SQL Server 2008, you can do this:
WHERE CONVERT(time(0), startHour) >= CONVERT(time(0), #startTime)
Here's a full test:
DECLARE #tbEvents TABLE (
timeEvent int IDENTITY,
startHour datetime
)
INSERT INTO #tbEvents (startHour) SELECT DATEADD(hh, 0, GETDATE())
INSERT INTO #tbEvents (startHour) SELECT DATEADD(hh, 1, GETDATE())
INSERT INTO #tbEvents (startHour) SELECT DATEADD(hh, 2, GETDATE())
INSERT INTO #tbEvents (startHour) SELECT DATEADD(hh, 3, GETDATE())
INSERT INTO #tbEvents (startHour) SELECT DATEADD(hh, 4, GETDATE())
INSERT INTO #tbEvents (startHour) SELECT DATEADD(hh, 5, GETDATE())
--SELECT * FROM #tbEvents
DECLARE #startTime datetime
SET #startTime = DATEADD(mi, 65, GETDATE())
SELECT
timeEvent,
CONVERT(time(0), startHour) AS 'startHour',
CONVERT(time(0), #startTime) AS '#startTime'
FROM #tbEvents
WHERE CONVERT(time(0), startHour) >= CONVERT(time(0), #startTime)
Just change convert datetime to time that should do the trick:
SELECT timeEvent
FROM tbEvents
WHERE convert(time, startHour) >= convert(time, #startHour)
if (cast('2012-06-20 23:49:14.363' as time) between
cast('2012-06-20 23:49:14.363' as time) and
cast('2012-06-20 23:49:14.363' as time))
One (possibly small) issue I have noted with the solutions so far is that they all seem to require a function call to process the comparison. This means that the query engine will need to do a full table scan to seek the rows you are after - and be unable to use an index. If the table is not going to get particularly large, this probably won't have any adverse affects (and you can happily ignore this answer).
If, on the other hand, the table could get quite large, the performance of the query could suffer.
I know you stated that you do not wish to compare the date part - but is there an actual date being stored in the datetime column, or are you using it to store only the time? If the latter, you can use a simple comparison operator, and this will reduce both CPU usage, and allow the query engine to use statistics and indexes (if present) to optimise the query.
If, however, the datetime column is being used to store both the date and time of the event, this obviously won't work. In this case if you can modify the app and the table structure, separate the date and time into two separate datetime columns, or create a indexed view that selects all the (relevant) columns of the source table, and a further column that contains the time element you wish to search for (use any of the previous answers to compute this) - and alter the app to query the view instead.
Using float does not work.
DECLARE #t1 datetime, #t2 datetime
SELECT #t1 = '19000101 23:55:00', #t2 = '20001102 23:55:00'
SELECT CAST(#t1 as float) - floor(CAST(#t1 as float)), CAST(#t2 as float) - floor(CAST(#t2 as float))
You'll see that the values are not the same (SQL Server 2005). I wanted to use this method to check for times around midnight (the full method has more detail) in which I was comparing the current time for being between 23:55:00 and 00:05:00.
Adding to the other answers:
you can create a function for trimming the date from a datetime
CREATE FUNCTION dbo.f_trimdate (#dat datetime) RETURNS DATETIME AS BEGIN
RETURN CONVERT(DATETIME, CONVERT(FLOAT, #dat) - CONVERT(INT, #dat))
END
So this:
DECLARE #dat DATETIME
SELECT #dat = '20080201 02:25:46.000'
SELECT dbo.f_trimdate(#dat)
Will return
1900-01-01 02:25:46.000
Use Datepart function: DATEPART(datepart, date)
E.g#
SELECT DatePart(#YourVar, hh)*60) +
DatePart(#YourVar, mi)*60)
This will give you total time of day in minutes allowing you to compare more easily.
You can use DateDiff if your dates are going to be the same, otherwise you'll need to strip out the date as above
You can create a two variables of datetime, and set only hour of date that your need to compare.
declare #date1 datetime;
declare #date2 datetime;
select #date1 = CONVERT(varchar(20),CONVERT(datetime, '2011-02-11 08:00:00'), 114)
select #date2 = CONVERT(varchar(20),GETDATE(), 114)
The date will be "1900-01-01" you can compare it
if #date1 <= #date2
print '#date1 less then #date2'
else
print '#date1 more then #date2'
SELECT timeEvent
FROM tbEvents
WHERE CONVERT(VARCHAR,startHour,108) >= '01:01:01'
This tells SQL Server to convert the current date/time into a varchar using style 108, which is "hh:mm:ss". You can also replace '01:01:01' which another convert if necessary.
I believe you want to use DATEPART('hour', datetime).
Reference is here:
http://msdn.microsoft.com/en-us/library/ms174420.aspx
I don't love relying on storage internals (that datetime is a float with whole number = day and fractional = time), but I do the same thing as the answer Jhonny D. Cano. This is the way all of the db devs I know do it. Definitely do not convert to string. If you must avoid processing as float/int, then the best option is to pull out hour/minute/second/milliseconds with DatePart()
I am assuming your startHour column and #startHour variable are both DATETIME; In that case, you should be converting to a string:
SELECT timeEvent
FROM tbEvents
WHERE convert(VARCHAR(8), startHour, 8) >= convert(VARCHAR(8), #startHour, 8)
below query gives you time of the date
select DateAdd(day,-DateDiff(day,0,YourDateTime),YourDateTime) As NewTime from Table
#ronmurp raises a valid concern - the cast/floor approach returns different values for the same time. Along the lines of the answer by #littlechris and for a more general solution that solves for times that have a minute, seconds, milliseconds component, you could use this function to count the number of milliseconds from the start of the day.
Create Function [dbo].[MsFromStartOfDay] ( #DateTime datetime )
Returns int
As
Begin
Return (
( Datepart( ms , #DateTime ) ) +
( Datepart( ss , #DateTime ) * 1000 ) +
( Datepart( mi , #DateTime ) * 1000 * 60 ) +
( Datepart( hh , #DateTime ) * 1000 * 60 * 60 )
)
End
I've verified that it returns the same int for two different dates with the same time
declare #first datetime
set #first = '1900-01-01 23:59:39.090'
declare #second datetime
set #second = '2000-11-02 23:56:39.090'
Select dbo.MsFromStartOfDay( #first )
Select dbo.MsFromStartOfDay( #second )
This solution doesn't always return the int you would expect. For example, try the below in SQL 2005, it returns an int ending in '557' instead of '556'.
set #first = '1900-01-01 23:59:39.556'
set #second = '2000-11-02 23:56:39.556'
I think this has to do with the nature of DateTime stored as float. You can still compare the two number, though. And when I used this approach on a "real" dataset of DateTime captured in .NET using DateTime.Now() and stored in SQL, I found that the calculations were accurate.
TL;DR
Separate the time value from the date value if you want to use indexes in your search (you probably should, for performance). You can: (1) use function-based indexes or (2) create a new column for time only, index this column and use it in you SELECT clause.
Keep in mind you will lose any index performance boost if you use functions in a SQL's WHERE clause, the engine has to do a scan search. Just run your query with EXPLAIN SELECT... to confirm this. This happens because the engine has to process EVERY value in the field for EACH comparison, and the converted value is not indexed.
Most answers say to use float(), convert(), cast(), addtime(), etc.. Again, your database won't use indexes if you do this. For small tables that may be OK.
It is OK to use functions in WHERE params though (where field = func(value)), because you won't be changing EACH field's value in the table.
In case you want to keep use of indexes, you can create a function-based index for the time value. The proper way to do this (and support for it) may depend on your database engine. Another option is adding a column to store only the time value and index this column, but try the former approach first.
Edit 06-02
Do some performance tests before updating your database to have a new time column or whatever to make use of indexes. In my tests, I found out the performance boost was minimal (when I could see some improvement) and wouldn't be worth the trouble and overhead of adding a new index.