COALESCE doccumentation

From: PG Doc comments form <noreply(at)postgresql(dot)org>
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Subject: COALESCE doccumentation
Date: 2019-04-27 20:26:57
Message-ID: 155639681797.1368.1856073093791885251@wrigleys.postgresql.org
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The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/11/functions-conditional.html
Description:

The documentation says:

"The COALESCE function returns the first of its arguments that is not null.
Null is returned only if all arguments are null. It is often used to
substitute a default value for null values when data is retrieved for
display, for example"

Which is NOT TRUE. In addition, it is obscure and misleading.

The COALESCE(<value expression>, ..., <value expression>) scans the list of
<value expression>s from left to right, determines the highest data type in
the list and returns the first non-NULL in the list, casting it to the
highest data type selected in the previous step, but if all the <value
expressions>s are NULL, the result is NULL. In case when any of the <value
expressions>s in the list cannot be evaluated to the highest data type then
exception is thrown.

Try, for example.

SELECT COALESCE(NULL, '12', 3, 1, 1); -- OK!
SELECT COALESCE(NULL, '12.2', 3.2, '1', 1.1); -- OK!
SELECT COALESCE(NULL, '1d2', 3, 1, 1); -- error
SELECT COALESCE(NULL, '12', 3, '1d', 1); -- cast error

Thanks.

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