Delete "Column Does Not Exist"

delete column does not exist

The problem is that you are using double quotes (") and single quotes (') interchangeably. SQL treats what's inside double quotes "" as an identifier (i.e., table name, proc name, column name, etc.), character constants need to be enclosed in single quotes

You can say:

delete from "Tasks" where id = 'fc1f56b5-ff41-43ed-b27c-39eac9354323'

R dplyr drop column that may or may not exist select(-name)

You can do:

diamonds %>% 
 select(-one_of("clarity"))

If there is a non-existing variable:

diamonds %>% 
 select(-one_of("clarity", "clearness"))

it returns a warning:

Warning message:
Unknown columns: `clearness` 

From dplyr 1.0.0, any_of() could be used:

diamonds %>% 
 select(-any_of(c("clarity", "clearness")))

Column doens't exists in PostgreSQL (WHERE column_name = column_value)

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'

SQL WHERE - Column (value) does not exist

use single quote for string value because double quote means column name

SELECT * FROM pg_roles WHERE rolname='rom_tut'

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