Question

I have two tables with firstname, lastname and amount.

I can do a left join:

select * from spi left join dp 
on spi.amount = dp.amount
and lower(spi.firstname) = lower(dp.firstname)
and lower(spi.lastname) = lower(dp.lastname);

which gives good results:

|#   |firstname     |lastname    |amount|dp.firstname |dp.lastname  |dp.amount
|----+--------------+------------+------+-------------+-------------+---------
|1   |saumeh synah  |s*****      |50.0  |             |             |
|2   |Neda          |M*****      |1000.0|             |             |
|3   |Mansoor       |B********** |100.0 |             |             |
|4   |Hanna         |W****       |50.0  |Hanna        |W****        |50.0
|5   |Kristen       |A****       |40.0  |Kristen      |A****        |40.0
|6   |David         |B******     |10.0  |David        |B******      |10.0

Now I want to select just the rows that are missing from dp.

So I write:

select * from ( 
select * from spi left join dp 
on spi.amount = dp.amount
and lower(spi.firstname) = lower(dp.firstname)
and lower(spi.lastname) = lower(dp.lastname) )
where dp.amount = null;

but I get the error

no such column: dp.amount

Why not?

Answer 1

The error is due to the derived table. Just try a simple query:

select spi.* 
from spi left join dp 
on spi.amount = dp.amount
and lower(spi.firstname) = lower(dp.firstname)
and lower(spi.lastname) = lower(dp.lastname) 
where dp.amount IS null ;