Adding a Horizontal Line

In the previous example you might want to add a fixed horizontal line on the chart to represent your target quantity. That's easy. Just add an extra plot with two points, one at the minimum date and one at the maximum date, both with the same value:

SELECT UNIX_TIMESTAMP(MIN(`Date`)),120 FROM `my_table`
UNION
SELECT UNIX_TIMESTAMP(MAX(`Date`)),120 FROM `my_table`;

For a horizontal line at the average quantity value, try this:

SELECT UNIX_TIMESTAMP(MIN(`Date`)),AVG(`quantity`) FROM `my_table`
UNION
SELECT UNIX_TIMESTAMP(MAX(`Date`)),AVG(`quantity`) FROM `my_table`;