Column doens't exists in PostgreSQL (WHERE column_name = column_value) [duplicate] - sql

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I have the following table in PostgreSQL:
id and grade are INTs, note and subject both VARCHARs
When I run the command:
SELECT * FROM grades
WHERE subject = "latin";
I get the following error:
In pgAdmin4:
ERROR: column "latin" does not exist
LINE 2: WHERE subject = "latin"
^
SQL state: 42703
Character: 37
And in cmd:
ERROR: column "latin" does not exist
LINE 1: SELECT * FROM upisi WHERE subject = "latin";
I'm coming from MySQL so I thought this would work.
Works fine if I put grade = something in the WHERE clause. Any idea why this might be the case?

Answer 1

You need single quotes for character constants. (double quotes are used to quote identifiers)
SELECT * FROM grades
WHERE subject = 'latin';
If you use WHERE subject = "latin", the DBMS expects "latin" to be a column name, which it is not.

Answer 2

It's as simple as the wrong type of quote marks. You wanted:
SELECT * FROM grades
WHERE subject = 'latin';
To explain:
Single quotes, like 'latin', are the standard way to write a string in standard SQL, and should work on all DBMSes.
Double quotes, in Postgres and some other DBMSes, are a way of quoting identifiers - so if your column name had a space in for some reason (there's not many good reasons to do it, but it's possible), then you might write SELECT * FROM grades WHERE "subject name" = 'latin' - "subject name" is the name of the column, 'latin' is a string.
Although double quotes are in the SQL standard, other DBMSes use different syntax for quoting identifiers, so may treat double quotes as an alternative for writing strings.
-- Postgres (also works in Microsoft SQL Server, but isn't the default style)
SELECT * FROM grades WHERE "subject name" = 'latin'
-- MySQL
SELECT * FROM grades WHERE `subject name` = 'latin'
-- Microsoft SQL Server
SELECT * FROM grades WHERE [subject name] = 'latin'
But if you always use single quotes for strings, and avoid names that need quoting, you'll run into fewer problems.
-- Works pretty much everywhere
SELECT * FROM grades WHERE subject = 'latin'