MySQL 8.0

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CREATE TABLE current (
 id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
 symbol VARCHAR(5), 
 INDEX (symbol)
);

INSERT INTO current (symbol) VALUES
('A'), ('B'), ('C'), ('C'), ('B'), ('A'), ('C'), ('C'), ('A'), ('B');

Records: 10  Duplicates: 0  Warnings: 0


WITH CTE AS (
    SELECT *
    , ROW_NUMBER() OVER (PARTITION BY symbol ORDER BY id DESC) AS symbol_rn
    FROM current
) 
SELECT id, symbol
FROM CTE
WHERE symbol_rn = 2
ORDER BY id;


id
symbol


5
B

6
A

7
C


SELECT c1.id, c1.symbol
FROM current c1
LEFT JOIN current c2
  ON c2.symbol = c1.symbol
 AND c2.id >= c1.id
GROUP BY c1.id, c1.symbol
HAVING COUNT(c2.id) = 2
ORDER BY c1.id;


id
symbol


5
B

6
A

7
C