Cypher on SQL stores: all(), any(), none() and single() are two-valued where the predicate is null
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Start at _quantifier() in drivine/cypher/sql/sql_cypher_compiler.py and compare its SQL generation with the described behavior in drivine4j and the cases in drivine-cypher-spec v0.6.7. Check how the generated query handles null predicates and null lists for all four quantifiers. Done means SQL stores match the stated three-valued Cypher semantics.
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描述
Port of liberation-data/drivine4j#272.
What happens: on the SQL stores, all(), any(), none() and single() are two-valued where the predicate is null. Cypher's quantifiers are three-valued: a quantifier whose predicate is null for some item, with no item that decides it, is null.
MATCH (n:Person) WHERE none(x IN [1] WHERE n.name IN ['Keanu']) RETURN count(n)
MATCH (n:Person) WHERE all(x IN [1] WHERE n.name = 'x') RETURN count(n)
For a node with no name, Neo4j drops the row, because the quantifier is null. The SQL stores keep it, because NOT EXISTS (… WHERE NOT cond) reads a null cond as true.
Expected: three-valued quantifiers, as drivine4j does since liberation-data/drivine4j#283:
- all(): false if any item is false, else null if any is null, else true;
- any(): true if any is true, else null if any is null, else false;
- none(): the negation of any();
- single(): null when a null item could change the count of true items around one.
drivine4j keeps the cheap EXISTS forms in a WHERE that reads only the truth, where the predicate can't be null. Otherwise it uses one scalar count subquery, mapped to 1/0/NULL and compared = 1, and guards a null list. The cases are in drivine-cypher-spec v0.6.7.
Where: _quantifier() in drivine/cypher/sql/sql_cypher_compiler.py.
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