Comparison operations like .==, ./=, .>, .>=, .< and .<= will produce NULLs if one of their arguments is NULL.

>>> printSQL $ true .== null_
(TRUE = NULL)

>>> printSQL $ true ./= null_
(TRUE <> NULL)

>>> printSQL $ true .>= null_
(TRUE >= NULL)

>>> printSQL $ true .< null_
(TRUE < NULL)

>>> printSQL $ true .<= null_
(TRUE <= NULL)

>>> printSQL $ true .> null_
(TRUE > NULL)

>>> let expr = greatest [param @1] currentTimestamp
>>> printSQL expr
GREATEST(($1 :: timestamp with time zone), CURRENT_TIMESTAMP)

>>> printSQL $ least [null_] currentTimestamp
LEAST(NULL, CURRENT_TIMESTAMP)

A RankNType for comparison expressions like between.

>>> printSQL $ true `between` (null_, false)
TRUE BETWEEN NULL AND FALSE

>>> printSQL $ true `notBetween` (null_, false)
TRUE NOT BETWEEN NULL AND FALSE

between, after sorting the comparison values

>>> printSQL $ true `betweenSymmetric` (null_, false)
TRUE BETWEEN SYMMETRIC NULL AND FALSE

not between, after sorting the comparison values

>>> printSQL $ true `notBetweenSymmetric` (null_, false)
TRUE NOT BETWEEN SYMMETRIC NULL AND FALSE

not equal, treating null like an ordinary value

>>> printSQL $ true `isDistinctFrom` null_
(TRUE IS DISTINCT FROM NULL)

equal, treating null like an ordinary value

>>> printSQL $ true `isNotDistinctFrom` null_
(TRUE IS NOT DISTINCT FROM NULL)

is true

>>> printSQL $ true & isTrue
(TRUE IS TRUE)

is false or unknown

>>> printSQL $ true & isNotTrue
(TRUE IS NOT TRUE)

is false

>>> printSQL $ true & isFalse
(TRUE IS FALSE)

is true or unknown

>>> printSQL $ true & isNotFalse
(TRUE IS NOT FALSE)

is unknown

>>> printSQL $ true & isUnknown
(TRUE IS UNKNOWN)

is true or false

>>> printSQL $ true & isNotUnknown
(TRUE IS NOT UNKNOWN)