PostgreSQL “Column does not exist” but it actually does

问题

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?

回答1:

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

SELECT "Continent"
FROM network.countries
...

回答2:

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' "))

回答3:

This problem occurs because in pgAdmin3 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:

来源：https://stackoverflow.com/questions/41591386/postgresql-column-does-not-exist-but-it-actually-does

标签

sql

postgresql

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