Missing FROM-clause entry for table " "", what to do?

Question

PostgreSQL

In the column, I indicated which table to take from, and he writes to me that there is no entry from the sentence for the "users" table, what should I do?

spoiler

Answer 1

In FROM, you need to specify the teterika.users table and the condition for linking to the teterika.lessons table.
if the condition is not specified, then each row of one table will be associated with each row of another table, a Cartesian product of the tables will be obtained.

SELECT 
  tl.subject,
  tu.role
FROM teterika.lessons AS tl, teterika.users AS tu
WHERE teterika.users.role = 'tutor'

By the way, your request does not make sense, because from teterika.users.role you will only extract the 'tutor' entry in accordance with the condition. Those. your request can be replaced with:

SELECT 
  tl.subject,
  'tutor' AS role
FROM teterika.lessons

Unless you really need to get the cartesian product of all lessons with all teachers.