Question

I have a table

id_user, hour, medition  
1 0  100  
1 1  101  
1 14 102  
2 5  108  
2 17 103

How I can complete the inexistent hours with a 0 value for any user?
example

1 0 100  
1 1 101  
1 2 0  
1 3 0  
...

Answer 1

build a table hours, populate it with the numbers from 1 to 24, then use this to query with an outer join against your primary table. – replace nulls with 0

edit to add quick example:

SELECT id_user, hour, NVL(medition,0)
FROM `hours` as h
LEFT JOIN `myTable`
    ON `hours`.`hour` = `myTable`.`hour`