Re: COALESCE doccumentation
Bruce Momjian <[email protected]>
| Newsgroups | gmane.comp.db.postgresql.devel.documentation |
|---|---|
| Message-ID | <[email protected]> |
On Sat, Apr 27, 2019 at 08:26:57PM +0000, PG Doc comments form wrote: > 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 What is a highest data type? The first data type? > 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 What is wrong about the existing description? That it doesn't mention mixing data types? -- Bruce Momjian <[email protected]> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +