Question

The following query:

select unnest(Table2.L) as X, unnest(Table1.O) 
from Table1, Table2 
where Table1.code = Table2.code 
order by X ;

produces the desired results. I would, however, like to exclude (unnested) rows which match some value. Adding a condition to the query, such as the following:

and unnest(Table2.L) != '-'

obviously does not work. Is this possible? How?

Answer 1

If by unnest(Table2.L) != '-' you mean

throw out all the unnested elements that are '-'

then use a derived table and filter out the unnested values you don’t want:

select *
from (
    select unnest(Table2.L) as X, unnest(Table1.O) 
    from Table1 join Table2 on Table1.code = Table2.code
) dt
where X != '-'
order by X ;

If you mean

ignore all rows from Table2 where L contains '-'

then you can use the @> operator to check if L contains a certain element:

select unnest(Table2.L) as X, unnest(Table1.O)
from Table1 join Table2 on Table1.code = Table2.code
where not Table1.L @> ARRAY['-']

or you could use ANY:

select unnest(Table2.L) as X, unnest(Table1.O)
from Table1 join Table2 on Table1.code = Table2.code
where not '-' = any(Table1.L)

And do yourself a favor by forgetting that implicit joins exist, always use explicit join conditions.