sql server - SQL conversion from varchar to datetime -

one of columns of sql server table mm:ss of varchar type mm = minutes , ss = seconds.

i need average of column.

should convert column datetime format first? if can tell me how? if not can tell me should do?

here failed attempt convert datetime :

select convert(datetime, '2014-01-01 '+pace+':00', 108) 

where pace varchar 23:05

if want average, convert column number of seconds , work that:

select avg(pace_secs) average_in_seconds (select cast(left(pace, 2) int) * 60 + cast(right(pace, 2) int) pace_secs       t      ) t; 

if want in format, can do:

select right('00' + cast(avg(pace_secs) / 60 int), 2) + ':' +        right('00' + avg(page_secs) % 60), 2)     (select cast(left(pace, 2) int) * 60 + cast(right(pace, 2) int) pace_secs           t          ) t;