select *
from blabla
where Dates like 'isNull(@day,__)+'/'+isNull(@month,__)+'/'+isNull(@year,__)'

тип Dates date

If @day is not null and @month is not null
Select *
From blabla
Where day(dates) =@day and month(dates)=@month

тип Dates date

If @day is not null and @month is not null
Select *
From blabla
Where day(dates) =@day and month(dates)=@month

Select *
From blabla
Where ( @day is null or day(dates) = @day ) and ( @month is null or month(dates) = @month )

create table dbo.DimDate (
	DateKey date primary key,
	DateYear smallint not null,
	DateMonth tinyint not null,
	DateDay tinyint not null
);

select ao.*
from sys.all_objects ao
	inner join dbo.DimDate d on cast(ao.create_date as date) = d.DateKey
where nullif(@day, d.DateDay) is null
	and nullif(@month, d.DateMonth) is null
	and nullif(@year, d.DateYear) is null;

DECLARE @d INT = NULL;
DECLARE @m INT = NULL;
DECLARE @y INT = NULL;
;
DECLARE @date_min DATE;
DECLARE @date_max DATE;
;
SELECT
  @date_min = MIN( create_date ),
  @date_max = DATEADD( DAY, 1, MAX( create_date ) )
FROM
  sys.all_objects
;
DECLARE @dates TABLE ( [date] DATE NOT NULL PRIMARY KEY );
WITH
d ( [date], [y], [m], [d] ) AS (
  SELECT
    [date] = @date_min,
    [y] = DATEPART( YEAR, @date_min ),
    [m] = DATEPART( MONTH, @date_min ),
    [d] = DATEPART( DAY, @date_min )
  UNION ALL
  SELECT
    [date] = ss.[date],
    [y] = DATEPART( YEAR, ss.[date] ),
    [m] = DATEPART( MONTH, ss.[date] ),
    [d] = DATEPART( DAY, ss.[date] )
  FROM
    d
    CROSS APPLY (
      SELECT [date] = DATEADD( DAY, 1, d.[date] )
    ) ss
  WHERE
    d.[date] < @date_max
)
INSERT
INTO @dates
SELECT
  [date]
FROM
  d
WHERE
      ISNULL( @d, d.[d] ) = d.[d]
  AND ISNULL( @m, d.[m] ) = d.[m]
  AND ISNULL( @y, d.[y] ) = d.[y]
OPTION (
  MAXRECURSION 0 )
;
SELECT 
  o.*
FROM 
  @dates d
  INNER JOIN sys.all_objects o ON (
        CONVERT( DATE, o.[create_date] ) = d.[date] )
;