Abstract
The design of SQL is based on a three-valued logic (3VL), rather than the familiar two-valued Boolean logic (2VL). In addition totrue andfalse, 3VL addsunknown to handle nulls. Viewed as indispensable for SQL expressiveness, it is often criticized for unintuitive behavior of queries and for being a source of programmer mistakes. We show that, contrary to the widely held view, SQL could have been designed based on 2VL, without any loss of expressiveness. Similarly to SQL's WHERE clause, which only keeps true tuples, we conflate false and unknown for conditions involving nulls to obtain an equally expressive 2VL-based version of SQL. This applies to the core of the 1999 SQL Standard. Queries written under the 2VL semantics can be efficiently translated into the 3VL SQL and thus executed on any existing RDBMS. We show that 2VL enables additional optimizations. To gauge its applicability, we establish criteria under which 2VL and 3VL semantics coincide, and analyze common benchmarks such as TPC-H and TPC-DS to show that most of their queries are such. For queries that behave differently under 2VL and 3VL, we undertake a user study to show a consistent preference for the 2VL semantics.
Original language | English |
---|---|
Title of host publication | PODS 2023 - Proceedings of the 42nd ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems |
Publisher | Association for Computing Machinery |
Pages | 11-20 |
Number of pages | 10 |
ISBN (Electronic) | 9798400701276 |
DOIs | |
State | Published - 18 Jun 2023 |
Externally published | Yes |
Event | 42nd ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems, PODS 2023 - Seattle, United States Duration: 18 Jun 2023 → 23 Jun 2023 |
Publication series
Name | Proceedings of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems |
---|
Conference
Conference | 42nd ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems, PODS 2023 |
---|---|
Country/Territory | United States |
City | Seattle |
Period | 18/06/23 → 23/06/23 |
Bibliographical note
Publisher Copyright:© 2023 ACM.
Keywords
- boolean logic
- nulls
- query equivalence
- query optimization
- SQL
- three-valued logic
- user study