IF EXISTS (
    SELECT * FROM sysobjects WHERE id = object_id(N'function_name')
    AND xtype IN (N'FN', N'IF', N'TF')
)
    DROP FUNCTION function_name
GO

IF object_id(N'function_name', N'FN') IS NOT NULL
    DROP FUNCTION function_name
GO

if object_id('FUNCTION_NAME') is not NULL
   DROP FUNCTION <name>

IF EXISTS (SELECT *
       FROM   sysobjects
           WHERE name='<function name>' and xtype='FN'

xtype in ('FN','TF')

IF OBJECT_ID('YourObjectName') IS NOT NULL

IF OBJECT_ID('YourFunction') IS NOT NULL
   DROP FUNCTION YourFunction
GO

IF EXISTS
(SELECT * FROM sys.objects
WHERE object_id = OBJECT_ID(N'functionName')
AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))

DROP FUNCTION functionName
GO

DROP FUNCTION [ IF EXISTS ] { [ schema_name. ] function_name } [ ,...n ]
    [;]

CREATE [ OR ALTER ] FUNCTION [ schema_name. ] function_name

IF EXISTS
      (SELECT *
      FROM schema.sys.objects
      WHERE name = 'func_name')
    DROP FUNCTION [dbo].[func_name]
GO

DROP Function IF EXISTS udf_name

if(object_id(N'[dbo].[fn_Nth_Pos]', N'FN')) is not null
    drop function [dbo].[fn_Nth_Pos];
GO
CREATE FUNCTION [dbo].[fn_Nth_Pos]
(
    @find char, --char to find
    @search varchar(max), --string to process
    @nth int --occurrence
)
RETURNS int
AS
BEGIN
    declare @pos int --position of nth occurrence
    --init
    set @pos = 0

    while(@nth > 0)
    begin
        set @pos = charindex(@find,@search,@pos+1)
        set @nth = @nth - 1
    end

    return @pos
END
GO

--EXAMPLE
declare @files table(name varchar(max));

insert into @files(name) values('abc_1_2_3_4.gif');
insert into @files(name) values('zzz_12_3_3_45.gif');

select
    f.name,
    dbo.fn_Nth_Pos('_', f.name, 1) as [1st],
    dbo.fn_Nth_Pos('_', f.name, 2) as [2nd],
    dbo.fn_Nth_Pos('_', f.name, 3) as [3rd],
    dbo.fn_Nth_Pos('_', f.name, 4) as [4th]
from
    @files f;

IF  EXISTS (SELECT TOP 1 1 FROM sys.objects WHERE
        object_id = OBJECT_ID(N'[Schema].[function_Name]')
         AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))
BEGIN
DROP FUNCTION [Schema].[function_Name]
Print('function dropped => [Schema].[function_Name]')
END
GO

IF EXISTS (
    SELECT ROUTINE_NAME FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_NAME = N'FunctionName'
)
   DROP FUNCTION [dbo].[FunctionName]
GO