Write data quality checks for this table

Before you trust a table you've just been handed.

Write a set of SQL checks that tell me whether the table below is trustworthy.

Cover:
1. **Uniqueness**: is the claimed key actually unique? Are there near-duplicates differing only by whitespace or case?
2. **Completeness**: NULL rate per column, and any column where NULL appears to encode something.
3. **Validity**: values outside plausible ranges, negative amounts, dates in the future or before the system existed, enum columns with unexpected values.
4. **Consistency**: referential integrity against parent tables, totals that should reconcile, mutually exclusive flags both set.
5. **Freshness and volume**: latest row timestamp, rows per day over the last 30 days, and any day with a suspicious gap or spike.

Give each check as a runnable query returning the offending rows or a count. Order them by how likely they are to find something. Say which failures would make the table unusable and which are merely noise.

Table and schema:

Schema and data quality. Designing tables, migrating them without breaking live code, and cleaning what you have been handed.