Previous order date
For every order, return `id`, `placed_on` and `prev_placed_on`: the date of that customer's previous order, or NULL for their first. Order by customer then date.
What a strong answer looks like
Say what the query is meant to return before you write it, and name the shape of the answer: how many rows, grouped by what. Then watch the NULLs and the duplicates, because that is where most of these are lost.
Run onlyA query runs as one statement, so there is nothing to step through. Run it and read the rows.
0:00 of about 13 min
query.sql
Expected, in this order
| id | placed_on | prev_placed_on |
|---|---|---|
| 1 | 2026-01-04 | NULL |
| 2 | 2026-01-19 | 2026-01-04 |
| 7 | 2026-03-03 | 2026-01-19 |
| 3 | 2026-01-21 | NULL |
| 4 | 2026-02-02 | 2026-01-21 |
| 6 | 2026-02-28 | 2026-02-02 |
1 more row
Your result
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