You are given a client list and a historical revenue table. Write a PostgreSQL query that returns every client from the client list, attaches the most recent revenue found in the revenue history, and uses a lookup default when no revenue exists. If a client has no matching revenue row, show 0 as the revenue amount and Unknown as the revenue source.
| Column | Type | Description |
|---|---|---|
| client_idPK | INT | Primary key for the client list |
| client_name | VARCHAR(100) | Client display name |
| segment | VARCHAR(50) | Client segment |
| Column | Type | Description |
|---|---|---|
| revenue_idPK | INT | Primary key for revenue rows |
| client_id | INT | Client identifier from the lookup table |
| revenue_month | DATE | Month the revenue was recorded |
| revenue_amount | NUMERIC(12,2) | Revenue amount for that month |
| revenue_source | VARCHAR(50) | Source system or feed name |