IPMT Function (Interest payment) - SQL Server

IPMT.sql

/** 
 * Interest Payment
 * (SQL Server) 
 * AzsaturnDx (2020) - No copyright at all
 *
 * Returns the interest payment for a given period for an investment based on periodic, constant payments and a constant interest rate.
 *
 * @Rate FLOAT - Required. The interest rate per period.
 * @Period INT - Required. Specifies the period and must be in the range 1 to nper.
 * @Periods INT - Required. The total number of payment periods in an annuity.
 * @Present FLOAT - Required. The present value — the total amount that a series of future payments is worth now.
 * @Future FLOAT - Optional. The future value, or a cash balance you want to attain after the last payment is made. If don't needed pass 0 as value
 * @Type - Optional. The number 0 or 1 and indicates when payments are due.
 * @return FLOAT Interest payment by given period
 *
 * @Example
 * 	  SELECT dbo.IPMT(0.00673,1,104,-50000,0,0)
 *
 * REQUIRES: dbo.PMT , dbo.FV
 * Required functions are available @: https://gist.github.com/Azsaturndx/8ce3e47e2d3210a65fc83b09ac32da5f
 */


CREATE FUNCTION [dbo].[IPMT]
	(@Rate FLOAT
	,@Period INT
	,@Periods INT
	,@Present FLOAT
	,@Future FLOAT
	,@Type INT)  
RETURNS FLOAT
    BEGIN   
	    SET @Type = ISNULL(@Type,0);
		DECLARE @Payment AS FLOAT = (SELECT dbo.PMT(@Rate,@Periods,@Present,@Future,@Type))
		DECLARE @Interest AS FLOAT = 0.0;
		
		IF @Period=1
		BEGIN
			IF @Type=1
			BEGIN
				SET @Interest=0
			END --IF @Type=1
			ELSE
			BEGIN
				SET @Interest=-@Present
			END 
		END --IF @Period=1
		ELSE --IF @Period <> 1
		BEGIN
			IF @Type=1
			BEGIN
				SET @Interest=dbo.FV(@Rate,@Period-2,@Payment,@Present,1)-@Payment
			END --IF @Type=1
			ELSE --IF @Type<>1
			BEGIN
				SET @Interest = dbo.FV(@Rate,@Period-1,@Payment,@Present,0)
			END --IF @Type<>1
		END ----IF @Period <> 1
		
        RETURN @Interest*@Rate
    END;