Combining (concatenating) date and time into a datetime - sql

Question

Using SQL Server 2008, this query works great:
select CAST(CollectionDate as DATE), CAST(CollectionTime as TIME)
from field
Gives me two columns like this:
2013-01-25 18:53:00.0000000
2013-01-25 18:53:00.0000000
2013-01-25 18:53:00.0000000
2013-01-25 18:53:00.0000000
.
.
.
I'm trying to combine them into a single datetime using the plus sign, like this:
select CAST(CollectionDate as DATE) + CAST(CollectionTime as TIME)
from field
I've looked on about ten web sites, including answers on this site (like this one), and they all seem to agree that the plus sign should work but I get the error:
Msg 8117, Level 16, State 1, Line 1
Operand data type date is invalid for add operator.
All fields are non-zero and non-null. I've also tried the CONVERT function and tried to cast these results as varchars, same problem. This can't be as hard as I'm making it.
Can somebody tell me why this doesn't work? Thanks for any help.

Answer 1

Assuming the underlying data types are date/time/datetime types:
SELECT CONVERT(DATETIME, CONVERT(CHAR(8), CollectionDate, 112)
+ ' ' + CONVERT(CHAR(8), CollectionTime, 108))
FROM dbo.whatever;
This will convert CollectionDate and CollectionTime to char sequences, combine them, and then convert them to a datetime.
The parameters to CONVERT are data_type, expression and the optional style (see syntax documentation).
The date and time style value 112 converts to an ISO yyyymmdd format. The style value 108 converts to hh:mi:ss format. Evidently both are 8 characters long which is why the data_type is CHAR(8) for both.
The resulting combined char sequence is in format yyyymmdd hh:mi:ss and then converted to a datetime.

Answer 2

The simple solution
SELECT CAST(CollectionDate as DATETIME) + CAST(CollectionTime as DATETIME)
FROM field

Answer 3

An easier solution (tested on SQL Server 2014 SP1 CU6)
Code:
DECLARE #Date date = SYSDATETIME();
DECLARE #Time time(0) = SYSDATETIME();
SELECT CAST(CONCAT(#Date, ' ', #Time) AS datetime2(0));
This would also work given a table with a specific date and a specific time field. I use this method frequently given that we have vendor data that uses date and time in two separate fields.

Answer 4

Cast it to datetime instead:
select CAST(CollectionDate as DATETIME) + CAST(CollectionTime as TIME)
from field
This works on SQL Server 2008 R2.
If for some reason you wanted to make sure the first part doesn't have a time component, first cast the field to date, then back to datetime.

Answer 5

DECLARE #ADate Date, #ATime Time, #ADateTime Datetime
SELECT #ADate = '2010-02-20', #ATime = '18:53:00.0000000'
SET #ADateTime = CAST (
CONVERT(Varchar(10), #ADate, 112) + ' ' +
CONVERT(Varchar(8), #ATime) AS DateTime)
SELECT #ADateTime [A nice datetime :)]
This will render you a valid result.

Answer 6

Solution (1): datetime arithmetic
Given #myDate, which can be anything that can be cast as a DATE, and #myTime, which can be anything that can be cast as a TIME, starting SQL Server 2014+ this works fine and does not involve string manipulation:
CAST(CAST(#myDate as DATE) AS DATETIME) + CAST(CAST(#myTime as TIME) as DATETIME)
You can verify with:
SELECT GETDATE(),
CAST(CAST(GETDATE() as DATE) AS DATETIME) + CAST(CAST(GETDATE() as TIME) as DATETIME)
Solution (2): string manipulation
SELECT GETDATE(),
CONVERT(DATETIME, CONVERT(CHAR(8), GETDATE(), 112) + ' ' + CONVERT(CHAR(8), GETDATE(), 108))
However, solution (1) is not only 2-3x faster than solution (2), it also preserves the microsecond part.
See SQL Fiddle for the solution (1) using date arithmetic vs solution (2) involving string manipulation

Answer 7

Concat date of one column with a time of another column in MySQL.
SELECT CONVERT(concat(CONVERT('dateColumn',DATE),' ',CONVERT('timeColumn', TIME)), DATETIME) AS 'formattedDate' FROM dbs.tableName;

Answer 8

drop table test
create table test(
CollectionDate date NULL,
CollectionTime [time](0) NULL,
CollectionDateTime as (isnull(convert(datetime,CollectionDate)+convert(datetime,CollectionTime),CollectionDate))
-- if CollectionDate is datetime no need to convert it above
)
insert test (CollectionDate, CollectionTime)
values ('2013-12-10', '22:51:19.227'),
('2013-12-10', null),
(null, '22:51:19.227')
select * from test
CollectionDate CollectionTime CollectionDateTime
2013-12-10 22:51:19 2013-12-10 22:51:19.000
2013-12-10 NULL 2013-12-10 00:00:00.000
NULL 22:51:19 NULL

Answer 9

This works in SQL 2008 and 2012 to produce datetime2:
declare #date date = current_timestamp;
declare #time time = current_timestamp;
select
#date as date
,#time as time
,cast(#date as datetime) + cast(#time as datetime) as datetime
,cast(#time as datetime2) as timeAsDateTime2
,dateadd(dayofyear,datepart(dayofyear,#date) - 1,dateadd(year,datepart(year,#date) - 1900,cast(#time as datetime2))) as datetime2;

Answer 10

dealing with dates, dateadd must be used for precision
declare #a DATE = getdate()
declare #b time(7) = getdate()
select #b, #A, GETDATE(), DATEADD(day, DATEDIFF(day, 0, #a), cast(#b as datetime2(0)))

Answer 11

I am using SQL Server 2016 and both myDate and myTime fields are strings. The below tsql statement worked in concatenating them into datetime
select cast((myDate + ' ' + myTime) as datetime) from myTable

Answer 12

SELECT CONVERT(DATETIME, CONVERT(CHAR(8), date, 112) + ' ' + CONVERT(CHAR(8), time, 108))
FROM tablename