PostgreSQL - 左连接 generate_series() 和表

Question

I use generate series to create a series of numbers from 0 to 200.

I have a table that contains dirtareas in mm² in a column called polutionmm2. What I need is to left join this table to the generated series, but the dirt area must be in cm² so /100. I was not able to make this work, as I can't figure out how I can connect a table to a series that has no name.

This Is what I have so far:

select  generate_series(0,200,1) as x,  cast(p.polutionmm2/100 as char(8)) as metric   
from x
    left join polutiondistributionstatistic as p on metric = x

error: relation X does not exist

Here is some sample data: https://dbfiddle.uk/?rdbms=postgres_13&fiddle=3d7d851887adb938819d6cf3e5849719

what I would need, is the first column (x) counting all the way from 0 to 200, and where there is a matching value, to show it in the second column.

Like this:

x, metric
0, 0
1, 1
2, 2
3, null
4, 4
5, null
... , ...
... , ...
200, null

Answer 1

You can put generate_series() in the FROM . So, I think you want something like this:

select gs.x, cast(p.polutionmm2/100 as char(8)) as metric
from generate_series(0,200,1) gs(x) left join
     p
     on gs.x = (p.polutionmm2/100);

I imagine there is also more to your query, because this doesn't do much that is useful.