I want to know if joining a table that has a primary key `x` with another table, tells us anything about the size of the resulting table, in instance consider the following query:

```
SELECT r.*,s.* FROM r, s WHERE r.a = s.x;

```

`r`and `s`are two arbitrary tables that contain respectively `n` and `m` tuples. If we consider `x` as a primary key of `s` does it change our perspective about the size of their join? or would it always vary between `0`, if `a`and `x`are never equal, and `n`(or `m`) if `a` and `x` are identical.