AI engineering glossary · SQL databases
What is three-valued logic?
Three-valued logic: The logic SQL uses for conditions, where the result can be true, false or unknown, because NULL makes some comparisons undecidable. A WHERE clause keeps only rows whose condition is true, dropping both false and unknown.
Three-valued logic: an example
NULL = NULL evaluates to unknown, and NOT (unknown) is still unknown, so WHERE NOT (x = 5) silently skips rows where x is NULL.
Related terms
More SQL databases terms
Where you learn it
Three-valued logic is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.