Head over to the SQL editor in the Supabase dashboard.

Create tables to keep track of data lineage:

```sql
CREATE TABLE data_events (
event_id SERIAL PRIMARY KEY,
event_type VARCHAR (255),
table_name VARCHAR (255),
column_name VARCHAR (255),
timestamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE data_sources (
source_id SERIAL PRIMARY KEY,
source_name VARCHAR (255),
description TEXT
);
```

Set up triggers to log data events automatically:

```sql
CREATE OR REPLACE FUNCTION log_insert() RETURNS TRIGGER AS $$
BEGIN
INSERT INTO data_events (event_type, table_name, column_name)
VALUES ('INSERT', TG_TABLE_NAME, column_name);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER after_insert
AFTER INSERT ON your_table
FOR EACH ROW
EXECUTE FUNCTION log_insert();
```

Do the same for UPDATE and DELETE events:

```sql
CREATE OR REPLACE FUNCTION log_update() RETURNS TRIGGER AS $$
BEGIN
INSERT INTO data_events (event_type, table_name, column_name)
VALUES ('UPDATE', TG_TABLE_NAME, column_name);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER after_update
AFTER UPDATE ON your_table
FOR EACH ROW
EXECUTE FUNCTION log_update();
```

```sql
CREATE OR REPLACE FUNCTION log_delete() RETURNS TRIGGER AS $$
BEGIN
INSERT INTO data_events (event_type, table_name, column_name)
VALUES ('DELETE', TG_TABLE_NAME, column_name);
RETURN OLD;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER after_delete
AFTER DELETE ON your_table
FOR EACH ROW
EXECUTE FUNCTION log_delete();
```

Fill up the data_sources table with details about your data sources:

```sql
INSERT INTO data_sources (source_name, description)
VALUES ('API Source A', 'Data from external API A');
```

Link data events to their sources as needed.

Write custom SQL queries to trace data lineage:

```sql
SELECT
event_id,
event_type,
table_name,
column_name,
timestamp
FROM
data_events
WHERE
table_name = 'your_table'
ORDER BY
timestamp DESC;
```