Where Filters

Where NULL Unknown

A comparison with NULL evaluates to UNKNOWN, and WHERE keeps only TRUE rows.

highlighted = computed this step

Input table

Start with shipments; some date cells are NULL.

Shipments\text{Shipments}
Shipmentsorder_idshipped_ono12026-01-05o2NULLo32026-01-07o4NULL

Where query

Compare each shipped date with the target date.

WHERE shipped date matches\text{WHERE shipped date matches}
WHERE shipped date equals targetwhere shipped_on eq 2026-01-05arity 2 rows 1Shipmentsarity 2 rows 4

Predicate truth

Rows with NULL dates evaluate to UNKNOWN, not TRUE.

TRUE, FALSE, UNKNOWN\text{TRUE, FALSE, UNKNOWN}
Three-valued truthrowtruth1TRUE2UNKNOWN3FALSE4UNKNOWN

Filtered output

Only the TRUE row passes the WHERE filter.

known match only\text{known match only}
Filtered outputorder_idshipped_ono12026-01-05