Three-Valued Logic
Learn null in SQL through a few examples using truth tables.
We'll cover the following
Given its relational theory background, SQL comes with a special value that has no counterpart in a common programming language: null
. In Python, we have None
; in PHP, we have null
; in C, we have nil
; and about every other programming language has something that looks like a null
.
The difference in SQL is that null
introduces three-valued logic. This is very different from other languages is that None
or Null
is used when comparing values. Let’s have a look at the SQL null
truth table:
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