PostgreSQL "Column does not exist" but it actually does

Question

I'm writing a Java application to automatically build and run SQL queries. For many tables my code works fine but on a certain table it gets stuck by throwing the following exception:

Exception in thread "main" org.postgresql.util.PSQLException: ERROR: column "continent" does not exist
  Hint: Perhaps you meant to reference the column "countries.Continent".
  Position: 8

The query that has been run is the following:

SELECT Continent
FROM network.countries
WHERE Continent IS NOT NULL
AND Continent <> ''
LIMIT 5

This essentially returns 5 non-empty values from the column.

I don't understand why I'm getting the "column does not exist" error when it clearly does in pgAdmin 4. I can see that there is a schema with the name Network which contains the table countries and that table has a column called Continent just as expected.

Since all column, schema and table names are retrieved by the application itself I don't think there has been a spelling or semantical error so why does PostgreSQL cause problems regardless? Running the query in pgAdmin4 nor using the suggested countries.Continent is working.

My PostgreSQL version is the newest as of now:

$ psql --version
psql (PostgreSQL) 9.6.1

How can I successfully run the query?

Answer 1

Try to take it into double quotes - like "Continent" in the query:

SELECT "Continent"
FROM network.countries
...

Answer 2

This problem occurs in postgres because the table name is not tablename instead it is "tablename". for eg. If it shows user as table name, than table name is "user".

See this:

Answer 3

In working with SQLAlchemy environment, i have got this error with the SQL like this,

   db.session.execute(
    text('SELECT name,type,ST_Area(geom) FROM buildings WHERE type == "plaza" '))

ERROR: column "plaza" does not exist

Well, i changed == by = , Error still persists, then i interchanged the quotes, like follows. It worked. Weird!

.... 
text("SELECT name,type,ST_Area(geom) FROM buildings WHERE type = 'plaza' "))

Answer 4

Such an error can appear when you add a space in the name of a column by mistake (for example "users ").

Answer 5

I got the same error when I do PIVOT in RedShift. My code is similar to

SELECT *
INTO output_table
FROM (
SELECT name, year_month, sales
FROM input_table
) 
PIVOT
(
SUM(sales)
FOR year_month IN ('nov_2020', 'dec_2020', 'jan_2021', 'feb_2021', 'mar_2021', 'apr_2021', 'may_2021', 'jun_2021', 'jul_2021', 'aug_2021',
                  'sep_2021', 'oct_2021', 'nov_2021', 'dec_2021', 'jan_2022', 'feb_2022', 'mar_2022', 'apr_2022', 'may_2022', 'jun_2022',
                  'jul_2022', 'aug_2022', 'sep_2022', 'oct_2022', 'nov_2022')
)

I tried year_month without any quote (got the error), year_month with double quote (got the error), and finally year_month with single quote (it works this time). This may help if someone in the same situation like my example.

Answer 6

QUICK FIX (TRICK)

If you have recently added a field which you have already deleted before and now trying to add the same field back then let me share you this simple trick! i did this and the problem was gone!!

so, now just delete the migration folder entirely on the app,then instead of adding that field you need to now add a field but with the name of which you have never declared on this app before, example if you are trying to add title field then create it by the name of heading and now do the migration process separately on the app and runserver, now go to admin page and look for that model and delete all the objects and come to models back and rename the field that you recently made and name it to which you were wishing it with earlier and do the migrations again and now your problem must have been gone!!

this occurs when the objects are there in the db but you added a field which wasn't there when the earlier objs were made, so by this we can delete those objs and make fresh ones again!