根据生日获取年龄不仅仅是“多少岁”，还可能涉及到年龄不到“1岁”、不到“1月”、不到“1天”、不到“1小时”、不到“1分钟”的情况，整理如下脚本，做以笔记：

DECLARE @BirthDate DATETIME
DECLARE @CurrentDate DATETIME
SET @BirthDate = '2014-04-29 12:59:00.000'
SET @CurrentDate = '2014-04-29 13:10:23.000'

DECLARE @DiffInYears INT
DECLARE @DiffInMonths INT
DECLARE @DiffInDays INT
DECLARE @DiffInHours INT
DECLARE @DiffInMinutes INT
DECLARE @DiffInSeconds INT
DECLARE @TotalSeconds BIGINT

-- Determine Year, Month, and Day differences
SET @DiffInYears = DATEDIFF(year, @BirthDate, @CurrentDate)
IF @DiffInYears > 0
    SET @BirthDate = DATEADD(year, @DiffInYears, @BirthDate)
IF @BirthDate > @CurrentDate
BEGIN
    -- Adjust for pushing @BirthDate into future
    SET @DiffInYears = @DiffInYears - 1
    SET @BirthDate = DATEADD(year, -1, @BirthDate)
END

SET @DiffInMonths = DATEDIFF(month, @BirthDate, @CurrentDate)
IF @DiffInMonths > 0
    SET @BirthDate = DATEADD(month, @DiffInMonths, @BirthDate)
IF @BirthDate > @CurrentDate
BEGIN
    -- Adjust for pushing @BirthDate into future
    SET @DiffInMonths = @DiffInMonths - 1
    SET @BirthDate = DATEADD(month, -1, @BirthDate)
END

SET @DiffInDays = DATEDIFF(day, @BirthDate, @CurrentDate)
IF @DiffInDays > 0
    SET @BirthDate = DATEADD(day, @DiffInDays, @BirthDate)
IF @BirthDate > @CurrentDate
BEGIN
    -- Adjust for pushing @BirthDate into future
    SET @DiffInDays = @DiffInDays - 1
    SET @BirthDate = DATEADD(day, -1, @BirthDate)
END

-- Get number of seconds difference for Hour, Minute, Second differences
SET @TotalSeconds = DATEDIFF(second, @BirthDate, @CurrentDate)

-- Determine Seconds, Minutes, Hours differences
SET @DiffInSeconds = @TotalSeconds % 60
SET @TotalSeconds = @TotalSeconds / 60

SET @DiffInMinutes = @TotalSeconds % 60
SET @TotalSeconds = @TotalSeconds / 60

SET @DiffInHours = @TotalSeconds

-- Display results
 SELECT @DiffInYears AS YearsDiff,
        @DiffInMonths AS MonthsDiff,
        @DiffInDays AS DaysDiff,
        @DiffInHours AS HoursDiff,
        @DiffInMinutes AS MinutesDiff,
        @DiffInSeconds AS SecondsDiff