MySQL 8.0

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CREATE TABLE UNION_SALES (location VARCHAR(45), current_Price INT);
CREATE procedure lower10_avg_price (loc varchar(45))
BEGIN

SET @a = (SELECT ceil(COUNT(*)/10) FROM UNION_SALES WHERE location = loc and current_Price >5000);

SET @quer = concat(
'SELECT ROUND(avg(prices.price),2)
FROM 
(SELECT current_Price as price FROM UNION_SALES WHERE location = ', loc,' and current_Price >5000
ORDER BY current_Price ASC LIMIT ?) as prices;');

SELECT @quer;
/*
PREPARE STMT FROM @quer;
EXECUTE STMT USING @a;
*/
END
CALL lower10_avg_price('Αρχαία Αγορά            ');


@quer


SELECT ROUND(avg(prices.price),2)
FROM 
(SELECT current_Price as price FROM UNION_SALES WHERE location = Αρχαία Αγορά             and current_Price >5000
ORDER BY current_Price ASC LIMIT ?) as prices;