In the case of these tables: 

Table a

```
id | val 
---+-------
1  | foo
2  | bar
3  | spam 

```

Table b

```
id | val 
---+-------
1  | foo
2  | bar
4  | eggs 

```

Table c

```
id | val 
---+-------
0  | gaa
2  | bar
3  | spam

```

How can I perform a join so the id column contains a list of all 3 tables? That is: 

```
id | val 
---+-------
0  | gaa
1  | foo
2  | bar
3  | spam
4  | eggs 

```