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I'm trying a SQL query with the function COALESCE in PostgreSQL 9.6.17, but it produces an error:

invalid syntax for type double precision: ""

Example query:

SELECT COALESCE(date_part('year', s.date_pp),'')
FROM public.sendoc s.

This query is working on PostgreSQL 9.3.17.

How to get around the error at the server DB level without changing the source code of the program?

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    I am really surprised this worked in 9.3 Commented Sep 7, 2020 at 14:55
  • @a_horse_with_no_name There might have been some custom implicit type casts. Commented Sep 8, 2020 at 2:56

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I don't think you can "fix" this without changing your query or going back to Postgres 9.3, where apparently type casting rules were more relaxed.

date_part() returns a floating point value, and in the absence of an implicit type cast Postgres tries to convert the other operand of coalesce() to a compatible value, and an empty string ('') cannot be so converted.

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  • Thanks for the answer. As I understand it, in the Postgres settings, there is no way to configure loyalty when an implicit type for resolve "fix"? Commented Sep 7, 2020 at 20:03
  • In my view, it was a bug that was fixed post-9.3. I don't know of a way to undo that in Postgres. If you're looking for a database that's quite liberal with type casts, try MySQL (though it'll probably hurt you in many other ways). Commented Sep 7, 2020 at 22:32
  • @ИванЛинюшин: the correct fix is, to fix your query, not Postgres (because 9.6 behaves correctly, the fact that this worked in 9.3 was a bug to begin with). Commented Sep 9, 2020 at 5:53
  • I'm using PostgreSQL CAST To Convert a Value of One Type to Another. SELECT COALESCE(CAST(date_part('year', s.date_pp) as VARCHAR),'') FROM public.sendoc s Commented Sep 9, 2020 at 10:27

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