"David G. Johnston" <david.g.johnston@gmail.com> writes: > On Sun, Jun 27, 2021 at 11:18 AM Allan Kamau <kamauallan@gmail.com> wrote: >> Is it possible to declare a UNIQUE constraint that uses GIN indexing?
> Doesn't seem to be possible. The btree_gin extension would provide the > necessary code but it states explicitly that: > "... and they lack one major feature of the standard B-tree code: the > ability to enforce uniqueness."
GIN stores all the component elements of its input values separately. It'd be tremendously hard even to identify which inputs share exactly the same component elements; let alone whether inputs sharing the same elements should be considered "equal". For example, ARRAY[1,2] and ARRAY[2,1] would give rise to identical sets of index entries in a GIN array_ops index.
In short, no, this isn't something you do with a GIN index.
regards, tom lane
Thank you David and Tom for your speedy and informative responses.