What's the difference between NOT EXISTS vs. NOT IN vs. LEFT JOIN WHERE IS NULL?

Question

It seems to me that you can do the same thing in a SQL query using either NOT EXISTS, NOT IN, or LEFT JOIN WHERE IS NULL. For example:

SELECT a FROM table1          


        

Answer 1

When need to insert data in table with multi-field primary key, consider that it will be much faster (I tried in Access but I think in any Database) not to check that "not exists records with 'such' values in table", - rather just insert into table, and excess records (by the key) will not be inserted twice.