Useful operators in SQL

True and false

In SQL false results are represented by 0 and true results are represented by 1. Any zero value is false and any non-zero value is true.

When comparing operators we can use SELECT as a general “execute” function for SQL to interpret

SELECT 0 = 0 -- 1
SELECT 0.0 = 0 -- 1
SELECT 9 >= 12 -- 0

Boolean operators

SQL supports all Boolean operators:

SELECT (9 > 7) AND (3 < 5) -- 1
SELECT (3 > 1) OR (2 > 5) -- 1
SELECT (3 > 1) XOR (5 > 1) -- 0

We also have IS and IS NOT for testing Boolean values:

SELECT (9 > 7) IS TRUE -- 1
SELECT (9 > 7) IS NOT TRUE -- 0

NULL

  • NULL is neither true (1) or false (0). It has no value.
  • An empty string ("") is not NULL
SELECT 1 IS NULL -- 0
SELECT 1 IS NOT NULL -- 1
SELECT NULL IS NULL -- 1
SELECT "" IS NULL -- 0
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