DROP IF EXISTS VS DROP?

Standard SQL syntax is

DROP TABLE table_name;

IF EXISTS is not standard; different platforms might support it with different syntax, or not support it at all. In PostgreSQL, the syntax is

DROP TABLE IF EXISTS table_name;

The first one will throw an error if the table doesn't exist, or if other database objects depend on it. Most often, the other database objects will be foreign key references, but there may be others, too. (Views, for example.) The second will not throw an error if the table doesn't exist, but it will still throw an error if other database objects depend on it.

To drop a table, and all the other objects that depend on it, use one of these.

DROP TABLE table_name CASCADE;
DROP TABLE IF EXISTS table_name CASCADE;

Use CASCADE with great care.

It is not what is asked directly. But looking for how to do drop tables properly, I stumbled over this question, as I guess many others do too.

From SQL Server 2016+ you can use

DROP TABLE IF EXISTS dbo.Table

For SQL Server <2016 what I do is the following for a permanent table

IF OBJECT_ID('dbo.Table', 'U') IS NOT NULL 
  DROP TABLE dbo.Table; 

Or this, for a temporary table

IF OBJECT_ID('tempdb.dbo.#T', 'U') IS NOT NULL
  DROP TABLE #T;