Documenting cleaning rules with COMMENT ON TABLE and COMMENT ON COLUMN

COMMENT ON saves a note on a table or a column, inside the database, where the next analyst will find it.

About 5–10 minutes · no sign-up needed

Example

Leaving notes on tables and columns

COMMENT ON TABLE orders IS 'One row per order. Cleaned every night.';
COMMENT ON COLUMN orders.revenue IS 'In dollars, after discounts.'

Result:

COMMENT ON TABLE, the table's name, IS, then the note in single quotes.
```
COMMENT ON TABLE orders IS 'One row per order. Cleaned every night.';
```

COMMENT ON COLUMN uses table.column.

COMMENT ON TABLE orders IS 'One row per order. Cleaned every night.';
COMMENT ON COLUMN orders.revenue IS 'In dollars, after discounts.';

Say what the data means and how it's cleaned: units, allowed values, who updates it.

COMMENT ON TABLE orders IS 'One row per order. Cleaned every night.';
COMMENT ON COLUMN orders.revenue IS 'In dollars, after discounts.';

Try each one in your head first, then open the answer.

1. Add this comment to the orders table: 'One row per order'.

COMMENT ON TABLE orders IS 'One row per order'

2. Add this comment to the revenue column of orders: 'In dollars, after discounts'.

COMMENT ON COLUMN orders.revenue IS 'In dollars, after discounts'

3. Add this comment to the orders table: 'Cleaned every night. Duplicates removed.'

COMMENT ON TABLE orders IS 'Cleaned every night. Duplicates removed.'

4. Add this comment to the order_date column of orders: 'The day the order was placed'.

COMMENT ON COLUMN orders.order_date IS 'The day the order was placed'

5. Add this comment to the category column of orders: 'Allowed: Electronics, Clothing, Home, Beauty'.

COMMENT ON COLUMN orders.category IS 'Allowed: Electronics, Clothing, Home, Beauty'

Learn it by doing. This lesson is a short hands-on level on Bampaa: see it work, then build and write it yourself, with instant feedback.

About 5–10 minutes · no sign-up needed