-- scalar %% / !%%: country only
SELECT 'E01000001'::gsscode % 'E';
 ?column? 
----------
 t
(1 row)

SELECT 'W01000001'::gsscode % 'E';
 ?column? 
----------
 f
(1 row)

SELECT 'W01000001'::gsscode !% 'E';
 ?column? 
----------
 t
(1 row)

SELECT 'E01000001'::gsscode !% 'E';
 ?column? 
----------
 f
(1 row)

-- scalar %% / !%%: country+type
SELECT 'E01000001'::gsscode % 'E01';
 ?column? 
----------
 t
(1 row)

SELECT 'E02000001'::gsscode % 'E01';
 ?column? 
----------
 f
(1 row)

-- scalar %%: full code behaves like =
SELECT 'E01000001'::gsscode % 'E01000001';
 ?column? 
----------
 t
(1 row)

SELECT 'E01000002'::gsscode % 'E01000001';
 ?column? 
----------
 f
(1 row)

-- invalid-length prefixes never match, no error
SELECT 'E01000001'::gsscode % 'E0100';
 ?column? 
----------
 f
(1 row)

SELECT 'E01000001'::gsscode % 'E0';
 ?column? 
----------
 f
(1 row)

SELECT 'E01000001'::gsscode % '';
 ?column? 
----------
 f
(1 row)

-- array form
SELECT 'E01000001'::gsscode % ARRAY['E01','E02'];
 ?column? 
----------
 t
(1 row)

SELECT 'E02000001'::gsscode % ARRAY['E01','E02'];
 ?column? 
----------
 t
(1 row)

SELECT 'W01000001'::gsscode % ARRAY['E01','E02'];
 ?column? 
----------
 f
(1 row)

SELECT 'E01000001'::gsscode !% ARRAY['S01','S02'];
 ?column? 
----------
 t
(1 row)

SELECT 'E01000001'::gsscode % ARRAY[]::text[];
 ?column? 
----------
 f
(1 row)

-- %% drives an index scan via the btree operator family
CREATE TEMP TABLE partial_sample (code gsscode);
INSERT INTO partial_sample
   SELECT ('E01' || lpad(i::text, 6, '0'))::gsscode FROM generate_series(1,50) i;
INSERT INTO partial_sample VALUES ('W01000001'), ('S01000001');
CREATE INDEX ON partial_sample USING btree (code);
ANALYZE partial_sample;
SELECT count(*) FROM partial_sample WHERE code % 'E01';
 count 
-------
    50
(1 row)