SET @City = 'London,Lyon,Kln';
SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(@City, ',',@r:=@r+1),',',-1) City
FROM (SELECT @r:=0) x,
(SELECT 'x' xx
    UNION
    SELECT 'v' xx
    UNION
    SELECT 'z' xx) z;

SET @City = 'London,Lyon,Kln';
SELECT *
FROM Invoices
WHERE City IN (
    SELECT SUBSTRING_INDEX(
        SUBSTRING_INDEX( @City, ',',@r:=@r+1),',',-1
    ) City
    FROM (SELECT @r:=0) x,
    (SELECT 'x' xx
        UNION
        SELECT 'v' xx
        UNION
        SELECT 'z' xx) z
)

SET @City = '"London","Lyon","Kln"';
SET @sql = concat('SELECT * FROM Invoices WHERE City IN (',@City,')');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;