Re: how to substract 2 fields of "hour type"

select LEFT(

  CAST(datediff(Hour,W.U_frmtime, W.U_totime) AS VARCHAR(100)),

  LEN( CAST(datediff(Hour,W.U_frmtime, W.U_totime) AS VARCHAR(100)))- 2)

  +':' +RIGHT( CAST(datediff(Hour,W.U_frmtime, W.U_totime) AS VARCHAR(100)), 2)

from [@TI_WIPHDR] W