php - Return positive value always even if it is negative -

select c.firstname,c.lastname,s.salesprice,p.recommendedprice,s.salesprice - p.recommendedprice  customers c inner join sales s on c.customerid=s.customerid inner join products p on s.productid=p.productid 

i know maths has function don't know specific function use in mysql.

i have difference table needs returned positive.

for example: difference -50 , want +50 in column.

according query s.salesprice - p.recommendedprice calculating price has refunded. put abs before calculation. below query

select c.firstname,c.lastname,s.salesprice,p.recommendedprice,abs(s.salesprice - p.recommendedprice)  customers c inner join sales s on c.customerid=s.customerid inner join products p on s.productid=p.productid 

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