计算两个时间相差多少年月日的sql算法

/****** Object:  StoredProcedure [dbo].[GetDateDiff]    Script Date: 11/12/2019 16:14:05 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
--计算两个时间相差多少年月日的sql算法，用于新生儿年龄计算
ALTER PROCEDURE [dbo].[GetDateDiff]
    @fromDate NVARCHAR(10) ,--开始日期
    @toDate NVARCHAR(10)    --结束日期
AS 
    DECLARE @YearDiff INTEGER
    DECLARE @MonthDiff INTEGER
    DECLARE @DayDiff INTEGER
    DECLARE @ToMonth INTEGER
    DECLARE @FromDay INTEGER
    DECLARE @ToDay INTEGER


    SET @YearDiff = LTRIM(DATEDIFF(yy, @fromDate, @toDate))
    SET @MonthDiff = LTRIM(DATEDIFF(mm, @fromDate, @toDate) % 12)
    SET @ToMonth = MONTH(CAST(@toDate AS DATETIME))
    SET @FromDay = DAY(CAST(@fromDate AS DATETIME))
    SET @ToDay = DAY(CAST(@ToDate AS DATETIME))
    IF ( @ToDay - @FromDay ) < 0 
        BEGIN
            IF ( @ToMonth - 1 ) = 1
                OR ( @ToMonth - 1 ) = 3
                OR ( @ToMonth - 1 ) = 5
                OR ( @ToMonth - 1 ) = 7
                OR ( @ToMonth - 1 ) = 8
                OR ( @ToMonth - 1 ) = 10
                OR ( @ToMonth - 1 ) = 12 
                BEGIN
                    SET @DayDiff = 31 + @Today - @FromDay
                    SET @MonthDiff = @MonthDiff - 1
                END    
            ELSE 
                BEGIN
                    SET @DayDiff = 30 + @Today - @FromDay
                    SET @MonthDiff = @MonthDiff - 1
                END
        END
    ELSE 
        BEGIN
            SET @DayDiff = @Today - @FromDay
        END
        
    SELECT  CAST(@YearDiff AS NVARCHAR(10)) + '岁'
            + CAST(@MonthDiff AS NVARCHAR(10)) + '个月'
            + CAST(@DayDiff AS NVARCHAR(10)) + '天'