How to write if else statement for this? - mysql

Question

I have the below code.
There is one which is one part which is "ISNULL(PO101_EXT_COST, 0)*MM01.MM021_RATE AS Amount, "
I will like to change to a if else statement.
When "MM01.MM021_RATE" = '1' then PO101_EXT_COST * MM021_FOREIGN_RATE
When "MM01.MM021_RATE" is not = '1' then PO101_EXT_COST * MM021_RATE
How can i change my code below?
SELECT
CASE
When MM01.MM021_RATE = 1
Then ISNULL(PO101_EXT_COST, 0)*MM01.MM021_FOREIGN_RATE
Else ISNULL(PO101_EXT_COST, 0)*MM01.MM021_RATE
END AS Amt END AS Amount,
ISNULL(IN100_INV_CODE,'') AS [Item Code],
ISNULL(IN006_DESC,'') AS Major,
ISNULL(IN007_DESC,'') AS Minor,
ISNULL(IN100_DESC,'') AS Item,
ISNULL(PO100_PO_REQ, 0) AS [PO #],
ISNULL(PO100_EVT_ID, 0) AS [Ev ID],
ISNULL(EV200_EVT_DESC, '') AS [Ev Desc],
ISNULL(PO101_EXT_COST, 0) AS OriginalAmt,
ISNULL(PO101_PHASE, '') AS Phase,
ISNULL(PO101_STATUS, '') AS Status,
ISNULL(EV870_ACCT_SECURITY,'') AS [ARCtl],
ISNULL(PO102_ACCOUNT,'') AS [GL Account],
MM01.MM021_EFFECTIVE_DATE,
MM01.MM021_RATE,
MM01.MM021_FOREIGN_RATE,
(PO101_ORG_CODE) AS ORG,
(PO101_CURRENCY) AS Currency, (PO100_APPROVAL) AS Approval
FROM PO101_ORD_DTL
LEFT OUTER JOIN PO100_ORDERS ON
PO100_ORG_CODE = PO101_ORG_CODE AND
PO100_PO_REQ = PO101_PO_REQ
LEFT JOIN PO102_DISTR ON
PO102_ORG_CODE = PO101_ORG_CODE AND
PO102_PO_REQ = PO101_PO_REQ AND
PO102_PO_REQ_SEQ = PO101_ORD_SEQ
LEFT OUTER JOIN EV200_EVENT_MASTER ON
PO100_ORG_CODE = EV200_ORG_CODE AND
PO100_EVT_ID = EV200_EVT_ID
LEFT OUTER JOIN MM021_CURRENCY_RATES MM01 ON
PO101_CURRENCY = MM01.MM021_CODE
INNER JOIN
(SELECT MM021_CODE, MAX(MM021_EFFECTIVE_DATE) AS EFFECTIVE_DATE
FROM MM021_CURRENCY_RATES
WHERE MM021_FOREIGN_RATE > 0 AND MM021_TO_CODE = '***'
GROUP BY MM021_CODE) MM02 ON
MM01.MM021_CODE = MM02.MM021_CODE AND
MM01.MM021_EFFECTIVE_DATE = MM02.EFFECTIVE_DATE
LEFT OUTER JOIN IN100_INV_MASTER ON
PO101_ITEM = IN100_INV_CODE AND
PO101_ORG_CODE = IN100_ORG_CODE
LEFT OUTER JOIN IN007_MINOR_GROUP ON
IN100_ORG_CODE = IN007_ORG_CODE AND
IN100_MINOR = IN007_MINOR AND
IN100_MAJOR = IN007_MAJOR
LEFT JOIN IN006_MAJOR_GROUP ON
IN006_ORG_CODE = IN007_ORG_CODE AND
IN006_MAJOR = IN007_MAJOR
LEFT JOIN EV870_ACCT_MASTER ON
PO101_BILLTO=EV870_ACCT_CODE AND
PO101_ORG_CODE=EV870_ORG_CODE
WHERE
(PO101_ORG_CODE = '40' ) AND
(EV200_EVT_DESC = 'Tyrexpo India 2016') AND
(ISNULL(PO100_APPROVAL,'') IN ('A9')) AND
(ISNULL(PO101_STATUS, '') IN ('O','C','H')) AND
(ISNULL(PO101_PHASE, '') IN ('1')) AND
(PO101_TAX_RES_TYPE <> '8APGST')
Thanks!

Answer 1

/*
DROP TABLE A;
DROP TABLE B;
CREATE TEMPORARY TABLE A (ID INT, rateid int,cost int);
CREATE TEMPORARY TABLE B(ID INT,rate int,foreignrate int);
TRUNCATE TABLE A;
INSERT INTO A VALUES(1,1,1),(2,1,null),(3,2,3),(4,2,null),(5,0,null),(6,7,null) ,(7,1,null) ,(8,0,null) ;
TRUNCATE TABLE B;
INSERT INTO B VALUES(1,10,20),(2,30,40);
*/
#SELECT A.* FROM A;
#SELECT B.* FROM B;
SELECT A.*,
case
when B.id = 1 then
case
when A.cost is not null and B.foreignrate is not null then A.cost * B.foreignrate
else 0
end
when B.id is not null then
case
when A.cost is not null and B.rate is not null then A.ID * B.rate
else 0
end
else 0
END AS AMT
FROM A
LEFT OUTER join B on B.ID = A.rateid