sql SUBSTRING的问题

    DECLARE @USERROWS NVARCHAR(MAX)
    SET @USERROWS=''
    SET @USERROWS='wode'
    print LEN(@USERROWS)
    SET @USERROWS=SUBSTRING(@USERROWS,0,LEN(@USERROWS))
    print @USERROWS     --结果为 wod
    
    DECLARE @USERROWS NVARCHAR(MAX)
    SET @USERROWS='wode'
    SET @USERROWS=SUBSTRING(@USERROWS,1,LEN(@USERROWS)-1)
    print @USERROWS     --结果为 wod