I have this usecase where I have a table 'a', which has the same columns as table 'b'. What I want is: for all rows that are both in 'a' and 'b', I want 'a' to have the same value for column 'x' as 'b'.

Here is what I'm trying but I keep getting stuck:

```
UPDATE a 
   SET a.x = b.x 
   FROM b  INNER JOIN  a  ON a.id = b.id;

```

Im getting errors: 

```
[Amazon](500310) Invalid operation: table name "a" specified more than once;

```

Any help would be greatly appreciated!