Sorry for my lame question I am new to the databases and SQL, Is the any SQL command for the finding out how many people are living in london from the database below? 

```
.....................
Name      | City   
.....................
John      | London  
Watson    | New York  
Sherlock  | London  
Holmes    | Berlin  
Mycroft   | innsbruck  
.....................

```

Secondly, are the commands for PostgresSQL, MySQL, SQLlite same?

Thanks!