sql server - SQL Date-Time Conversion with nested converts experiences random conversion errors -

looking assistance strange issue if has ideas:

i have sql statement works of time in t-sql script crashes occasionally. have identified data crash occurs on , cannot identify difference between data rows work.

the goal of code add time existing datetime value has 00:00:00 time second time column (as outlined below). goal combine both columns yyyy-mm-dd hh:mm:ss format, had convert them char first trim off orignal 00:00:00.

columns

logdate - contains date in datetime format (yyyy-mm-dd hh:mm:ss)

logtime - contains time of action , in varchar format (hh:mm)

sql conversion

select convert(datetime, convert(char(8), logdate, 112) + ' ' + convert(char(8), logtime, 108))                  testtable                 eventserial = '100001' 

however, if change eventserial in above statement different row, such '100002', statement works.

the data each row below:

eventserial 100001's values: logdate: 2015-04-02 00:00:00.000 logtime: 10:04

eventserial 100002's values: logdate: 2015-04-02 00:00:00.000 logtime: 10:48

running data set 1 fails, running data set 2 produces output. also, running code without final datetime conversion works, or if run code string manually works (as outlined below:)

select convert(char(8), logdate, 112) + ' ' + convert(char(8), logtime, 108)                  testtable                 eventserial = '100001'   select  convert(datetime, '20150402 10:48') select  convert(datetime, '20150402 10:04')  

any suggestions, i'm sure silly i'm missing (and took long way around issue anyway. desired output 2015-04-02 10:04:00

first, datetime has no format. (why?)

second, don't need convert datetime value char add hours , minutes, use dateadd:

select dateadd(minute,                 cast(right(logtime, 2) int),                 dateadd(hour,                         cast(left(logtime, 2) int),                         logdate                    )               )  testtable eventserial = '100001' 

also, note convert not hold style yyyymmdd hh:mm

note: code written directly here, there might mistakes.