WITH RECURSIVE nqueens_columns AS (
    SELECT 8 as columns
    UNION
    SELECT columns - 1 AS columns
    FROM nqueens_columns
    WHERE columns > 1
) SELECT 
    CONCAT(CHAR(x1 + 64), y1) AS queen1,
    CONCAT(CHAR(x2 + 64), y2) AS queen2,
    CONCAT(CHAR(x3 + 64), y3) AS queen3,
    CONCAT(CHAR(x4 + 64), y4) AS queen4,
    CONCAT(CHAR(x5 + 64), y5) AS queen5,
    CONCAT(CHAR(x6 + 64), y6) AS queen6,
    CONCAT(CHAR(x7 + 64), y7) AS queen7,
    CONCAT(CHAR(x8 + 64), y8) AS queen8
FROM (
    SELECT 1 AS x1, columns AS y1 
    FROM nqueens_columns
) as queen1
JOIN
(
    SELECT 2 AS x2, columns AS y2
    FROM nqueens_columns
) AS queen2
ON NOT (
    y1 = y2
    OR x1 - y1 = x2 - y2
    OR x1 + y1 = x2 + y2
)
JOIN
(
    SELECT 3 AS x3, columns AS y3
    FROM nqueens_columns
) AS queen3
ON NOT (
    y1 = y3
    OR x1 - y1 = x3 - y3
    OR x1 + y1 = x3 + y3
    OR y2 = y3
    OR x2 - y2 = x3 - y3
    OR x2 + y2 = x3 + y3
)
JOIN
(
    SELECT 4 AS x4, columns AS y4
    FROM nqueens_columns
) AS queen4
ON NOT (
    y1 = y4
    OR x1 - y1 = x4 - y4
    OR x1 + y1 = x4 + y4
    OR y2 = y4
    OR x2 - y2 = x4 - y4
    OR x2 + y2 = x4 + y4
    OR y3 = y4
    OR x3 - y3 = x4 - y4
    OR x3 + y3 = x4 + y4
)
JOIN
(
    SELECT 5 AS x5, columns AS y5
    FROM nqueens_columns
) AS queen5
ON NOT (
    y1 = y5
    OR x1 - y1 = x5 - y5
    OR x1 + y1 = x5 + y5
    OR y2 = y5
    OR x2 - y2 = x5 - y5
    OR x2 + y2 = x5 + y5
    OR y3 = y5
    OR x3 - y3 = x5 - y5
    OR x3 + y3 = x5 + y5
    OR y4 = y5
    OR x4 - y4 = x5 - y5
    OR x4 + y4 = x5 + y5
)
JOIN
(
    SELECT 6 AS x6, columns AS y6
    FROM nqueens_columns
) AS queen6
ON NOT (
    y1 = y6
    OR x1 - y1 = x6 - y6
    OR x1 + y1 = x6 + y6
    OR y2 = y6
    OR x2 - y2 = x6 - y6
    OR x2 + y2 = x6 + y6
    OR y3 = y6
    OR x3 - y3 = x6 - y6
    OR x3 + y3 = x6 + y6
    OR y4 = y6
    OR x4 - y4 = x6 - y6
    OR x4 + y4 = x6 + y6
    OR y5 = y6
    OR x5 - y5 = x6 - y6
    OR x5 + y5 = x6 + y6
)
JOIN
(
    SELECT 7 AS x7, columns AS y7
    FROM nqueens_columns
) AS queen7
ON NOT (
    y1 = y7
    OR x1 - y1 = x7 - y7
    OR x1 + y1 = x7 + y7
    OR y2 = y7
    OR x2 - y2 = x7 - y7
    OR x2 + y2 = x7 + y7
    OR y3 = y7
    OR x3 - y3 = x7 - y7
    OR x3 + y3 = x7 + y7
    OR y4 = y7
    OR x4 - y4 = x7 - y7
    OR x4 + y4 = x7 + y7
    OR y5 = y7
    OR x5 - y5 = x7 - y7
    OR x5 + y5 = x7 + y7
    OR y6 = y7
    OR x6 - y6 = x7 - y7
    OR x6 + y6 = x7 + y7
)
JOIN
(
    SELECT 8 AS x8, columns AS y8
    FROM nqueens_columns
) AS queen8
ON NOT (
    y1 = y8
    OR x1 - y1 = x8 - y8
    OR x1 + y1 = x8 + y8
    OR y2 = y8
    OR x2 - y2 = x8 - y8
    OR x2 + y2 = x8 + y8
    OR y3 = y8
    OR x3 - y3 = x8 - y8
    OR x3 + y3 = x8 + y8
    OR y4 = y8
    OR x4 - y4 = x8 - y8
    OR x4 + y4 = x8 + y8
    OR y5 = y8
    OR x5 - y5 = x8 - y8
    OR x5 + y5 = x8 + y8
    OR y6 = y8
    OR x6 - y6 = x8 - y8
    OR x6 + y6 = x8 + y8
    OR y7 = y8
    OR x7 - y7 = x8 - y8
    OR x7 + y7 = x8 + y8
);