StackOverflow Question #39656655, PostgreSQL

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CREATE TABLE cell (id SERIAL PRIMARY KEY, letters VARCHAR(4), parent_cell_id INT REFERENCES cell (id));

INSERT INTO cell (letters, parent_cell_id) VALUES ('A', NULL);
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AA', (SELECT id FROM cell WHERE letters = 'A'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AAA', (SELECT id FROM cell WHERE letters = 'AA'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AAC', (SELECT id FROM cell WHERE letters = 'AA'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AB', (SELECT id FROM cell WHERE letters = 'A'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AE', (SELECT id FROM cell WHERE letters = 'A'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AEA', (SELECT id FROM cell WHERE letters = 'AE'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AEE', (SELECT id FROM cell WHERE letters = 'AE'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('AEEB', (SELECT id FROM cell WHERE letters = 'AEE'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('B', NULL);
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BA', (SELECT id FROM cell WHERE letters = 'B'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BAA', (SELECT id FROM cell WHERE letters = 'BA'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BD', (SELECT id FROM cell WHERE letters = 'B'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BDC', (SELECT id FROM cell WHERE letters = 'BD'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BDCB', (SELECT id FROM cell WHERE letters = 'BDC'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BDCE', (SELECT id FROM cell WHERE letters = 'BDC'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BDD', (SELECT id FROM cell WHERE letters = 'BD'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BDDA', (SELECT id FROM cell WHERE letters = 'BDD'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BE', (SELECT id FROM cell WHERE letters = 'B'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BED', (SELECT id FROM cell WHERE letters = 'BE'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('BEDA', (SELECT id FROM cell WHERE letters = 'BED'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('C', NULL);
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CC', (SELECT id FROM cell WHERE letters = 'C'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CCB', (SELECT id FROM cell WHERE letters = 'CC'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CCBC', (SELECT id FROM cell WHERE letters = 'CCB'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CCBE', (SELECT id FROM cell WHERE letters = 'CCB'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CCC', (SELECT id FROM cell WHERE letters = 'CC'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CCCA', (SELECT id FROM cell WHERE letters = 'CCC'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CCCE', (SELECT id FROM cell WHERE letters = 'CCC'));
    INSERT INTO cell (letters, parent_cell_id) VALUES ('CE', (SELECT id FROM cell WHERE letters = 'C'));

WITH RECURSIVE rcte AS (
       SELECT id, letters
       FROM cell 
       WHERE letters = 'A'
       UNION ALL
       SELECT c.id, c.letters
       FROM cell c
       INNER JOIN rcte r
       ON c.parent_cell_id = r.id
    )
    SELECT letters
    FROM rcte
    ORDER BY letters;


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