Re: create unique constraint on jsonb->filed during create table

On Wednesday, February 27, 2019, Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> wrote:

>
> The following way works with 2 commands:
>
> zhifan=# create table t1 (a jsonb);
> CREATE TABLE
> zhifan=# create unique index t1_a_name on t1 ((a->'name'));
> CREATE INDEX
>
> but know I want to merge them into 1 command, is it possible?
>
> zhifan=# create table t2 (a jsonb, constraint uk_t2_a_name
> unique((a->'name')));
> ERROR: syntax error at or near "("
> LINE 1: ...table t2 (a jsonb, constraint uk_t2_a_name unique((a->'name'...
>

Not according to the documentation. Unique table constraints can only
reference columns in the table as a whole. An expression index must be
created separately from the table to which it is attached.

Or add a trigger to the table, populate an actual second column (making it
unique), and add a table check constraint that that column and the
expression are equal. I suspect you’ll be happier having the PK as actual
column data anyway.

David J.