Comment 4 for bug 1695911

Stumbled on this while doing some local refactoring... Dan, I think with the UNIQUE INDEX the table constraint is not necessary. We have something like this locally:

BEGIN;

ALTER TABLE metabib.browse_entry
    DROP CONSTRAINT browse_entry_sort_value_value_key;
DROP INDEX metabib.browse_entry_sort_value_idx;

CREATE INDEX browse_entry_sort_value_idx
    ON metabib.browse_entry (SUBSTRING(sort_value FROM 1 FOR 2700));

CREATE UNIQUE INDEX browse_entry_sort_value_value_key
    ON metabib.browse_entry
    USING btree (MD5(value), MD5(sort_value));

COMMIT;

Duplicate inserts on metabib.browse_entry will result in unique constraint violations.
If this looks sane, I can push a working branch.