Select MySQL only if floating point number changes

Question

I have the following data table:

Table name entity_values

Date Time	value
2017-09-02 05:05:00	20
2017-09-02 05:10:00	20
2017-09-02 05:15:00	21
2017-09-02 05:20:00	21
2017-09-02 05:25:00	21
2017-09-02 05:30:00	22

I currently only want to see changes, so I constructed the following query:

SELECT date_time AS 'time',
 value - LAG(value) over (order by date_time) as 'Kwh01-Energy (kWh)'
FROM entity_values;

This will return the following results:

Date Time	value
2017-09-02 05:00:00	0
2017-09-02 05:05:00	0
2017-09-02 05:10:00	1
2017-09-02 05:15:00	0
2017-09-02 05:20:00	0
2017-09-02 05:25:00	1

Since the window function does not allow to be used in the WHERE clause, such as:

SELECT date_time AS 'time',
 value - LAG(value) over (order by date_time) as 'Kwh01-Energy (kWh)'
FROM entity_values
WHERE (value - LAG(value) over (order by date_time)) > 0;

Error code: 3593. You cannot use the window function "lag" in this context.

Question: How to filter out 0 values ​​and only get the "changed" values? Desired result:

Date Time	value
2017-09-02 05:10:00	1
2017-09-02 05:25:00	1

Answer 1

Thanks @Andrew

SELECT t.* from (
SELECT 
date_time,
value - LAG(value) over (order by date_time) as changed_value
FROM entity_values 
) as t 
WHERE changed_value > 0