MySQL 8.0

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CREATE TABLE sales (
  `salesId` VARCHAR(20),
  `salesDate` VARCHAR(10)
);

INSERT INTO sales
  (`salesId`, `salesDate`)
VALUES
  ('7', '2017-05-15'),
  ('8', '2017-06-16'),
  ('9', '2017-07-18'),
  ('10', '2017-08-20');
    update sales
set salesId = case
                when month(salesDate)>=4 then concat(salesId,concat("/",year(salesDate),"-",year(salesDate)+1))
                else
                    concat(salesId,concat("/",year(salesDate)-1,"-",year(salesDate)))
                end
where cast(salesId as unsigned) between "7" and "10";
SELECT *  from sales


salesId
salesDate


7/2017-2018
2017-05-15

8/2017-2018
2017-06-16

9/2017-2018
2017-07-18

10/2017-2018
2017-08-20


 update sales
set salesId = case
                when month(salesDate)>=4 then concat(SUBSTRING_INDEX(salesId,'/',1),concat("/",year(salesDate),"-",year(salesDate)+1))
                else
                    concat(SUBSTRING_INDEX(salesId,'/',1),concat("/",year(salesDate)-1,"-",year(salesDate)))
                end
where cast(SUBSTRING_INDEX(salesId,'/',1) as unsigned) between "7" and "10";
SELECT *  from sales


salesId
salesDate


7/2017-2018
2017-05-15

8/2017-2018
2017-06-16

9/2017-2018
2017-07-18

10/2017-2018
2017-08-20

salesId	salesDate
7/2017-2018	2017-05-15
8/2017-2018	2017-06-16
9/2017-2018	2017-07-18
10/2017-2018	2017-08-20