If I have multiple left join statements and I have to apply `where` conditions like `x="string1"`, how do I apply them to individual left join statement?

More in a situation like this?

```
SELECT 
W.[ABC],
A.[XYZ]

FROM BLAH1 B0

LEFT JOIN WebUnion W ON B0.ID=W.ID
LEFT JOIN AppUnion A ON B0.ID=A.ID

WHERE WBC is null
AND
WHERE WBC is not null

```