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<p>Why do most (all?) SQL databases give the following results: </p> <pre class="brush:php;toolbar:false;">SELECT FALSE < FALSE; -- FALSE / 0 Ok SELECT TRUE < FALSE; -- FALSE / 0 Ok SELECT NOT(FALSE) < FALSE; -- TRUE / 1 What? SELECT NOT(TRUE) < FALSE; -- TRUE / 1 What? ? </pre> <p>Just to double-check: </p> <pre class="brush:php;toolbar:false;">SELECT NOT(TRUE) = FALSE; -- TRUE / 1 Ok SELECT NOT(FALSE) = TRUE; -- TRUE / 1 Ok</pre> <p>In Postgres I can also check: </p> <pre class="brush:php;toolbar:false;">SELECT pg_typeof(TRUE), pg_typeof(NOT(FALSE)); -- boolean | boolean</pre> <p>I've tried PostgreSQL, SQLite3 and MariaDB and they all gave the same unexpected results. </p><p> <strong>What am I missing? </strong></p>

SELECT (NOT FALSE) < FALSE; -- 0，與 TRUE < FALSE 相同
SELECT (NOT TRUE) < FALSE; -- 0，與 FALSE < FALSE 相同