On conjunctive queries containing inequalities
Journal of the ACM (JACM)
Optimization of real conjunctive queries
PODS '93 Proceedings of the twelfth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Hilbert's tenth problem
Containment of conjunctive queries: beyond relations as sets
ACM Transactions on Database Systems (TODS)
The complexity of querying indefinite data about linearly ordered domains
Journal of Computer and System Sciences - Special issue: dedicated to the memory of Paris Kanellakis
On the complexity of the containment problem for conjunctive queries with built-in predicates
PODS '98 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Deciding equivalences among aggregate queries
PODS '98 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Rewriting aggregate queries using views
PODS '99 Proceedings of the eighteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Equivalences Among Relational Expressions with the Union and Difference Operators
Journal of the ACM (JACM)
ADBIS '98 Proceedings of the Second East European Symposium on Advances in Databases and Information Systems
Optimal implementation of conjunctive queries in relational data bases
STOC '77 Proceedings of the ninth annual ACM symposium on Theory of computing
Equivalence of queries combining set and bag-set semantics
Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Proceedings of the 12th International Conference on Database Theory
Containment of conjunctive queries on annotated relations
Proceedings of the 12th International Conference on Database Theory
Privacy policy enforcement for health information data access
Proceedings of the 1st ACM international workshop on Medical-grade wireless networks
Equivalence of queries that are sensitive to multiplicities
The VLDB Journal — The International Journal on Very Large Data Bases
Equivalence of SQL queries in presence of embedded dependencies
Proceedings of the twenty-eighth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Query containment under bag and bag-set semantics
Information Processing Letters
Database theory: query languages
Algorithms and theory of computation handbook
The impact of virtual views on containment
Proceedings of the VLDB Endowment
Efficient auditing for complex SQL queries
Proceedings of the 2011 ACM SIGMOD International Conference on Management of data
The homomorphism domination exponent
European Journal of Combinatorics
Classification of annotation semirings over query containment
PODS '12 Proceedings of the 31st symposium on Principles of Database Systems
Equivalence and minimization of conjunctive queries under combined semantics
Proceedings of the 15th International Conference on Database Theory
Classification of annotation semirings over containment of conjunctive queries
ACM Transactions on Database Systems (TODS)
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Query containment is a fundamental algorithmic problem in database query processing and optimization. Under set semantics, the query-containment problem for conjunctive queries has long been known to be NP-complete. In real database systems, however, queries are usually evaluated under bag semantics, not set semantics. In particular, SQL queries are evaluated under bag semantics and return multisets as answers, since duplicates are not eliminated unless explicitly requested. The exact complexity of the query-containment problem for conjunctive queries under bag semantics has been an open problem for more than a decade; in fact, it is not even known whether this problem is decidable.Here, we investigate, under bag semantics, the query-containment problem for conjunctive queries with inequalities. It has been previously shown that, under set semantics, this problem is complete for the second level of the polynomial hierarchy. Our main result asserts that, under bag semantics, the query-containment problem for conjunctive queries with inequalities is undecidable. Actually, we establish the stronger result that this problem is undecidable even if the following two restrictions hold at the same time: (1) the queries use just a single binary relation; and (2) the total number of inequalities is bounded by a certain fixed value. Moreover, the same undecidability results hold under bag-set semantics.