Greg Stark wrote:
> MAX and MIN are single-parameter aggregate functions. LEAST and GREATEST are
> two-parameter (though in postgres they could be defined for 3 and more
> parameters) scalar functions.
If LEAST and GREATEST can accept any number of parameters, wouldn't it
make sense to code it like the way COALESCE works, rather than defining
a function for it? This way we don't need define all the various
functions with different types.
e.g.
SELECT greatest(a, b, c) FROM bar;
becomes
SELECT greatest(a, greatest(b, c)) from bar;
becomes
SELECT CASE WHEN b < c THEN CASE WHEN c < a THEN a ELSE c END ELSE CASE WHEN b < a
THEN a ELSE b END END
FROM bar;
From the docs:
COALESCE and NULLIF are just shorthand for CASE expressions. They are
actually converted into CASE expressions at a very early stage of
processing, and subsequent processing thinks it is dealing with CASE.
Thus an incorrect COALESCE or NULLIF usage may draw an error message
that refers to CASE.
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