Fetch JSONB Value for UNIQUE Constraint

Dear Hackers,

Should this work?

CREATE TABLE things (
user_id INTEGER NOT NULL,
document JSONB NOT NULL,
UNIQUE (user_id, document->>'name')
);
ERROR: syntax error at or near "->>"
LINE 4: UNIQUE (user_id, document->>’name')

I tried adding parens, but that didn’t work, either:

CREATE TABLE things (
user_id INTEGER NOT NULL,
document JSONB NOT NULL,
UNIQUE (user_id, (document->>'name'))
);
ERROR: syntax error at or near "("
LINE 4: UNIQUE (user_id, (document->>'name'))

It works fine to create a unique index, though:

CREATE TABLE things (
user_id INTEGER NOT NULL,
document JSONB NOT NULL
);
CREATE UNIQUE INDEX ON things(user_id, (document->>'name'));

So it’s a fine workaround, but maybe there’s something missing from the parsing of the CREATE TABLE statement? This is on 9.6.1.

Best,

David