Error in SQL query with lag windowing function

Eric Auld :

I'm working on a problem on Leetcode about SQL. The problem gives a table called Weather, with entries for Id (as in, id of a temperature measurement), Temperature, and RecordDate. Each Id comes from a subsequent day. They ask for the Ids where the temperature that day exceeded the temperature the previous day.

My attempt was

select id
    from
        (select id, temperature, lag(temperature, 1) over (ORDER BY RecordDate) prevs
            from weather)
    where temperature > prevs  

but it tells me there's a syntax error near the (ORDER BY... part.

What's wrong?

Yogesh Sharma :

Your query syntactical incorrect :

First, if you use LAG() with position parameter then you must specify the third parameter too. However, by default it is 1. So, don't need to specify :

LAG(temperature) over (ORDER BY RecordDate) AS prevs_temp

Second, your sub-query doesn't have alias :

select t.id
from (select id, temperature, LAG(temperature) over (ORDER BY RecordDate) AS prevs_temp
      from weather
     ) t -- alias missing 
where (t.temperature > t.prevs_temp or t.prevs_temp is null); -- will return id which doesn't have previous `temperature`.