Where Filters

Where NULL Date Exercise

This check focuses on the SQL rule that UNKNOWN rows do not pass a WHERE filter.

highlighted = computed this step

Input table

Start with shipments where some date cells are NULL.

exercise input with NULLs\text{exercise input with NULLs}
Shipmentsorder_idshipped_ono12026-01-05o2NULLo32026-01-07o4NULL

Where query

Compare each row with the target shipped date.

shipped date equals target\text{shipped date equals target}
WHERE shipped date equals targetwhere shipped_on eq 2026-01-07arity 2 rows 1Shipmentsarity 2 rows 4

Predicate truth

A NULL date becomes UNKNOWN, not a match.

TRUE versus UNKNOWN check\text{TRUE versus UNKNOWN check}
Three-valued truthrowtruth1FALSE2UNKNOWN3TRUE4UNKNOWN

Filtered output

The recomputed output keeps only the TRUE row.

checked output\text{checked output}
Filtered outputorder_idshipped_ono32026-01-07