PostgreSQL compatibility: json_array_length does not interpret arg as json

[emarsden]

What happens?

In PostgreSQL, the query select json_array_length('[]') returns 0.

In PGDuckDB, the query triggers an error function json_array_length(unknown) is not unique.

To Reproduce

pgeltestdb=# SELECT json_array_length('[]');
ERROR:  function json_array_length(unknown) is not unique
LIGNE 1 : SELECT json_array_length('[]');
                 ^
ASTUCE : Could not choose a best candidate function. You might need to add explicit type casts.

OS:

Linux

pg_duckdb Version (if built from source use commit hash):

Current Dockerhub image docker.io/pgduckdb/pgduckdb:18-main

Postgres Version (if built from source use commit hash):

PostgreSQL 18.3 (Debian 18.3-1.pgdg12+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14+deb12u1) 12.2.0, 64-bit

Hardware:

No response

Full Name:

Eric Marsden

Affiliation:

None

What is the latest build you tested with? If possible, we recommend testing with the latest nightly build.

I have tested with a stable release

Did you include all relevant data sets for reproducing the issue?

Yes

Did you include all code required to reproduce the issue?

• Yes, I have

Did you include all relevant configuration (e.g., CPU architecture, Linux distribution) to reproduce the issue?

• Yes, I have