PartiQL Specification Clarification on MISSING propogation and predicates.

[RCHowell]

Current

Since no function (other than IS MISSING) has MISSING as an input argument type, it follows that all functions return MISSING when one of their inputs is MISSING. – Section 7.1

As far as the boolean connectives and IS NULL are concerned a NULL input and a MISSING input behave identically. – Section 8 (Where Clause)

Contradictions?

• IS MISSING is referred to as a “function” rather than a special-form, operator, predicate, boolean connective, etc.. (interesting wording, but ok).
• Keep in mind that “all functions return MISSING when one of their inputs is MISSING”
• IS NULL does not return MISSING when one of its inputs is MISSING.
• Similarly both AND and OR do not return MISSING when one of its inputs is MISSING.

Takeaway

• The primary strangeness is mixing special-form predicate semantics with scalar function semantics.
• We should update all functions return MISSING when one of their inputs is MISSING to drop the parenthetical as it creates contradictions with later sections.
• Predicates should have their semantics decoupled from “functions” as they have special handling of null.

Updated

All functions return MISSING if any of its inputs is MISSING. – Section 7.1

All predicates treat MISSING as NULL (other than IS MISSING) and follow SQL’s 3-valued logic. The predicate IS MISSING doest not treat MISSING as NULL which allows distinguishing between NULL and MISSING.

NULL IS MISSING;    -- false

MISSING IS MISSING; -- true

[RCHowell]

PartiQL is missing the SQL-92 boolean test which may need some explanation for MISSING handling.

IS [NOT] (TRUE|FALSE|UNKNOWN)

[RCHowell]

Similarly, logical operators (NOT, AND, OR) can take missing as operand(s) and never returns MISSING.