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SQL's Three-Valued Logic and Certain Answers

Leonid Libkin
2016 ACM Transactions on Database Systems  
In practice, on the other hand, query answering must be very efficient, and to achieve this, SQL uses three-valued logic for evaluating queries on databases with nulls.  ...  This yields relatively small changes to the evaluation procedure, which we consider at the level of both declarative (relational calculus) and procedural (relational algebra) queries.  ...  Acknowledgment I thank Chris Date, Hugh Darwen, Ron Fagin, and Cristina Sirangelo for discussions, comments and suggestions.  ... 
doi:10.1145/2877206 fatcat:mfmbkc2cpnblhey5i65moj7zgm

Null values in SQL

John Grant
2008 SIGMOD record  
In various writings over the past 20 years, such as [3], Date has pointed out that SQL produces incorrect answers to some queries where a null value is included in a table.  ...  The purpose of this article is to show that, contrary to Rubinson's claim, Date's critique of query evaluation in the presence of null values in SQL is completely justified.  ...  Codd introduced the relational database model including the relational calculus, relational algebra, and relational database normalization.  ... 
doi:10.1145/1462571.1462575 fatcat:ob3qrr6isfbqnfh45pjgn4k3su

A formal semantics of SQL queries, its validation, and applications

Paolo Guagliardo, Leonid Libkin
2017 Proceedings of the VLDB Endowment  
One is the first formal proof of the equivalence of basic SQL and relational algebra that extends to bag semantics and nulls.  ...  We consider the basic class of SQL queries -essentially SELECT-FROM-WHERE queries with subqueries, set/bag operations, and nulls -and define a formal semantics for it, without any departures from the real  ...  Work partially supported by EPSRC grants N023056 and M025268.  ... 
doi:10.14778/3151113.3151116 fatcat:kriv2vdpdffuheayjuvldzmx5e

Comprehending nulls [article]

James Cheney, Wilmer Ricciotti
2021 arXiv   pre-print
However, SQL's treatment of incomplete information, using nulls and three-valued logic, is not compatible with 'standard' NRC based on two-valued logic.  ...  The Nested Relational Calculus (NRC) has been an influential high-level query language, providing power and flexibility while still allowing translation to standard SQL queries.  ...  and Industrial Strategy (BEIS).  ... 
arXiv:2107.11347v1 fatcat:6r6z3mru3nh6fet6lhjwf2k2zi

Query processing over object views of relational data

Gustav Fahl, Tore Risch
1997 The VLDB journal  
Therefore it must be possible to process queries that combine local data residing in the object view with data retrieved from the relational database.  ...  Such a view mechanism makes it possible for users to transparently work with data in a relational database as if it was stored in an objectoriented (OO) database.  ...  This research was supported by the Swedish Research Counsil for Engineering Sciences (NUTEK) and the Center for Industrial Information Technology (CENIIT).  ... 
doi:10.1007/s007780050045 fatcat:oqgcscweezhdxc6ad53qod4utq

Correctness of SQL Queries on Databases with Nulls

Paolo Guagliardo, Leonid Libkin
2017 SIGMOD record  
However, SQL evaluation can be modified, at least for relational algebra queries, to approximate certain answers, i.e., return only correct answers.  ...  As a result, the evaluation of SQL queries on databases with nulls may produce answers that are just plain wrong.  ...  Acknowledgments This survey is based on the work originally published in [15, 25] , which greatly benefited from discussions with  ... 
doi:10.1145/3156655.3156657 fatcat:ayak6sw7zvartmstd4s2kq7nam

Making SQL Queries Correct on Incomplete Databases

Paolo Guagliardo, Leonid Libkin
2016 Proceedings of the 35th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems - PODS '16  
Multiple issues with SQL's handling of nulls have been well documented.  ...  By analyzing the reasons for this, we come up with a new modified way of rewriting SQL queries that restores correctness.  ...  Work partially supported by EPSRC grants J015377 and M025268.  ... 
doi:10.1145/2902251.2902297 dblp:conf/pods/GuagliardoL16 fatcat:54iidxhs7vfd7ojt2x3kjqzvya

Do We Need Many-valued Logics for Incomplete Information?

Marco Console, Paolo Guagliardo, Leonid Libkin
2019 Proceedings of the Twenty-Eighth International Joint Conference on Artificial Intelligence  
They describe incomplete knowledge with three truth values, using Kleene's logic for propositional formulae and a rather peculiar extension to predicate calculus.  ...  by null values is no more powerful than the usual two-valued logic with the standard Boolean interpretation of the connectives.  ...  Acknowledgments This work was partly supported by EPSRC grants M025268 and N023056.  ... 
doi:10.24963/ijcai.2019/851 dblp:conf/ijcai/ConsoleGL19 fatcat:ygefts4zznbabdxkd3knhpp4y4

Translating Canonical SQL to Imperative Code in Coq [article]

Véronique Benzaken and Évelyne Contejean and Mohammed Houssem Hachmaoui and Chantal Keller and Louis Mandel and Avraham Shinnar and Jérôme Siméon
2022 arXiv   pre-print
SQL is by far the most widely used and implemented query language. Yet, on some key features, such as correlated queries and NULL value semantics, many implementations diverge or contain bugs.  ...  Finally, we develop a mechanized translation from the nested relational algebra to Imp, using the nested relational calculus as an intermediate step.  ...  The intuition for that translation is that the structure of relational algebra operators (e.g., , ) is preserved, but "administrative" steps are added to deal with NULL values and the SQL evaluation context  ... 
arXiv:2203.08941v2 fatcat:6sfe5o5j3besdp4o63yvvrpodi

Statistical Database Query Languages

G. Ozsoyoglu, Z.M. Ozsoyoglu
1985 IEEE Transactions on Software Engineering  
This paper surveys the existing and proposed SDB data definition and data manipulation (i.e., query) languages.  ...  SDB users, and 2) to apply statistical data analysis techniques that range from simple summary statistics to advanced procedures.  ...  JANUS utilizes relations with set-valued attributes and null values, and a set of relational algebra-like operators.  ... 
doi:10.1109/tse.1985.231854 fatcat:t25buguywffsjkd522awi3z3ca

The Un-Structured Student

Colin Myers, Paul Douglas
2007 24th British National Conference on Databases (BNCOD'07)  
We note, that many standard database textbooks introduce relational algebra (and indeed relation calculus) before SQL.  ...  However, SQL is closer to an implementation of a relational calculus than a relational algebra and thus students find the mapping of SQL onto the latter unnecessarily complicated.  ... 
doi:10.1109/bncod.2007.22 dblp:conf/bncod/MyersD07 fatcat:5az2vncdebb2rkmpyig7furuui

Coping with Incomplete Data: Recent Advances

Marco Console, Paolo Guagliardo, Leonid Libkin, Etienne Toussaint
2020 Proceedings of the 39th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems  
Work on the semantics of SQL was in conjunction with our collaboration with Neo4j Inc, supported by a grant from them.  ...  ACKNOWLEDGMENTS Most results presented here were obtained by the authors while they were supported by EPSRC projects M025268 "VADA: Value Added Data Systems" and N023056 "Managing Incomplete Data -New  ...  Queries in standard languages such as relational algebra, calculus, Datalog, etc., cannot invent new values, i.e., return constants that are not in the active domain.  ... 
doi:10.1145/3375395.3387970 dblp:conf/pods/ConsoleGLT20 fatcat:j62xnjuxfbfx7bskzmf6hcg27a

Polystore mathematics of relational algebra

Hayden Jananthan, Ziqi Zhou, Vijay Gadepally, Dylan Hutchison, Suna Kim, Jeremy Kepner
2017 2017 IEEE International Conference on Big Data (Big Data)  
Specifically, SQL Relational Algebra deals primarily with relations - multisets of tuples - and operations on and between these relations.  ...  Prior work presented the SQL relational model in terms of associative arrays and identified key mathematical properties that are preserved within SQL.  ...  Specifically, SQL Relational Algebra deals primarily with relations -multisets of tuples -and operations on and between those relations.  ... 
doi:10.1109/bigdata.2017.8258298 dblp:conf/bigdataconf/JananthanZGHKK17 fatcat:untcimz7v5grrhye4qidcmhfim

Incomplete data

Leonid Libkin
2014 Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '14  
customer ⊥ 1 ⊥ 2 ⊥ 3 customer product ⊥ 1 'SQL Standard' ⊥ 2 'Database Systems' ⊥ 3 'Logic' Some nulls can repeat and denote the same value.  ...  relational algebra (σ, π, ⋊ ⋉, ∪)  ...  Summary We can achieve correctness and efficiency at the same time. What we needed to do: Questions?  ... 
doi:10.1145/2594538.2594561 dblp:conf/pods/Libkin14 fatcat:bxl22q3y5naxpfdrk3m6bnkwq4

Towards testing of full-scale SQL applications using relational symbolic execution

Michaël Marcozzi, Wim Vanhoof, Jean-Luc Hainaut
2014 Proceedings of the 6th International Workshop on Constraints in Software Testing, Verification, and Analysis - CSTVA 2014  
SQL runtime errors and deal with non-deterministic SQL.  ...  We investigate the additional research work needed to integrate relational and dynamic symbolic execution, handle properly dynamic SQL, generate tractable SMT constraints for most SQL applications, detect  ...  In practice, this idea should be refined, as SQL is more powerful [12] than relational algebra, since it allows non-relational constructs like rows ordering and aggregation, null values, built-in or  ... 
doi:10.1145/2593735.2593738 dblp:conf/icse/MarcozziVH14 fatcat:y5b5hn2gfbdaxn5jifhh57w7uq
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