The table operator except all returns the rows of the first result except those that are also in the second.
SELECT …
FROM …
EXCEPT ALL
SELECT …
FROM …As with all table operators both sides of except must have the same number of columns and their types must be compatible based on their position (see corresponding). All null values are considered being the same (not distinct) for this operation.
Each occurrence of a row-value in the second result will remove one appearance of this row-value from the first result.
Related
Other table operators:
Union:
union [distinct],union allIntersect:
intersect [distinct],intersect all
Normative References
The except all operator is defined in ISO/IEC 9075-2:2023 as the optional feature F304, “EXCEPT ALL table operator”.

