The Big Idea
What if your database could think beyond just yes or no and handle 'maybe' too?
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Why Three-valued logic (TRUE, FALSE, UNKNOWN) in SQL? - Purpose & Use Cases
The Scenario
Imagine you have a list of people and their phone numbers, but some phone numbers are missing. You want to find everyone who has a phone number starting with '555'. You try to check each phone number manually, but what do you do when the phone number is missing? You get stuck.
The Problem
Manually checking each entry is slow and confusing. If you treat missing data as false or true, you get wrong answers. You might miss people who actually have numbers or include those who don't. This makes your results unreliable and wastes time.
The Solution
Three-valued logic helps by adding a third option: UNKNOWN. Instead of just TRUE or FALSE, it knows when data is missing. This way, your queries handle missing information correctly and give you accurate results without confusion.
Before vs After
✗ Before
WHERE phone LIKE '555%' OR phone IS NULL✓ After
WHERE phone LIKE '555%'What It Enables
It lets your database understand and work with missing or unknown data safely and correctly.
Real Life Example
When filtering customers who have made a purchase, some records might not have purchase dates yet. Three-valued logic helps you find only those who definitely made purchases, ignoring unknown or missing data without errors.
Key Takeaways
Manual checks fail with missing data.
Three-valued logic adds UNKNOWN to TRUE and FALSE.
This improves accuracy and trust in query results.