How can you find records that are not present in the first table when you have an incremental table with the same structure?

Question

Assisting AI · Accepted Answer

To identify rows that exist in the incremental table but not in the source table, you can use a LEFT JOIN with a NULL check or a NOT EXISTS subquery. For example:

```sql
SELECT i.*
FROM incremental_table i
LEFT JOIN source_table s
  ON i.id = s.id
WHERE s.id IS NULL;
```

This returns all rows from `incremental_table` whose primary key `id` does not match any row in `source_table`. Alternatively, using NOT EXISTS:

```sql
SELECT i.*
FROM incremental_table i
WHERE NOT EXISTS (
  SELECT 1 FROM source_table s WHERE s.id = i.id
);
```

Both approaches run in O(n) time relative to the number of rows, assuming an index on the join key. The choice depends on readability and database optimizer preferences. The key idea is to compare the unique identifiers of the two tables and filter out matches, leaving only the new or missing records.

How can you find records that are not present in the first table when you have an incremental table with the same structure?

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