如何比较存储在 Postgresql 中一列中的年份之间的日期？

Question

I have this output:

It's data of stock symbol, closing values and the year of the closing of the stock. I make the output from this query:

select symbol, close, extract(year from time) as tahun 
from (select * from (select * from tabel1 where close > (select avg(close) from tabel1)) 
      as result where open < close) as result group by symbol, close, tahun

Now, I want to find the 2016 closing values that has higher value than year 2017 (2016 > 2017). I'm stuck, please anyone can help?

[EDIT]

This is the original data:

How I define closing value for a year:

1. I extract all the closing values that has higher values than averag closing values. Here's the query:

select * from tabel1 where close > (select avg(close) from tabel1)

2. Then, from query above I extract the closing values that has higher values than the opening (open < close). Here's the query:

select * from (select * from tabel1 where close > (select avg(close) from tabel1)) as result where open < close

3. From the second output, I tried to group the data by symbol and find the 2016 closing values that has higher values than 2017 closing values. But I'm stuck with this query, seems that I don't know how to compare between the years that stored in one column:

select symbol, close, extract(year from time) as tahun 
from (select * from (select * from tabel1 where close > (select avg(close) from tabel1)) as result where open < close) as result group by symbol, close, tahun

Answer 1

You can use window functions with filtering:

select t.*
from (select t.*,
             max(close) filter (where tahun = 2016) over (partition by symbol) as close_2016
      from table1 t
     ) t
where tahun = 2017 and close < close_2016;

Or, if you prefer, a correlated subquery:

select t.*
from table1 t
where t.tahun = 2017 and
      t.close < (select tt.close from table1 tt where tt.symbol = t.symbol and tt.tahun = 2016);