Eight Queens - Revision history

John: /* SQL Eight Queens in SQL */

2024-05-16T07:50:35Z

SQL Eight Queens in SQL

John: Created page with "== SQL Eight Queens in SQL == '''Create the board:''' CREATE TABLE rows ( id integer PRIMARY KEY ); INSERT INTO rows (id) VALUES (1),(2),(3),(4),(5),(6)..."

2024-05-16T07:37:35Z

Created page with "== SQL Eight Queens in SQL == '''Create the board:''' <source lang="sql"> CREATE TABLE rows ( id integer PRIMARY KEY ); INSERT INTO rows (id) VALUES (1),(2),(3),(4),(5),(6)..."

New page

== SQL Eight Queens in SQL ==

'''Create the board:'''
<source lang="sql">
CREATE TABLE rows (
id integer PRIMARY KEY
);
INSERT INTO rows (id) VALUES (1),(2),(3),(4),(5),(6),(7),(8);

CREATE TABLE cols (
id integer PRIMARY KEY
);
INSERT INTO cols (id) VALUES (1),(2),(3),(4),(5),(6),(7),(8);
</source>

'''Get a set of queens:'''
<source lang="sql">
SELECT
cols.id AS col1, rows.id AS row1,
col2, row2,
col3, row3,
col4, row4,
col5, row5,
col6, row6,
col7, row7,
col8, row8
FROM rows, cols, (SELECT
col3, row3,
col4, row4,
col5, row5,
col6, row6,
col7, row7,
col8, row8,
rows.id AS row2, cols.id AS col2
FROM rows, cols, (SELECT
col4, row4,
col5, row5,
col6, row6,
col7, row7,
col8, row8,
rows.id AS row3, cols.id AS col3
FROM rows, cols, (SELECT
col5, row5,
col6, row6,
col7, row7,
col8, row8,
rows.id AS row4, cols.id AS col4
FROM rows, cols, (SELECT
col6, row6,
col7, row7,
col8, row8,
rows.id AS row5, cols.id AS col5
FROM rows, cols, (SELECT
col7, row7,
col8, row8,
rows.id AS row6, cols.id AS col6
FROM rows, cols, (SELECT
col8, row8,
rows.id AS row7, cols.id AS col7
FROM rows, cols, (SELECT
rows.id AS row8, cols.id AS col8
FROM rows, cols)
AS b8
WHERE cols.id != col8 AND rows.id != row8
AND (cols.id + rows.id != col8 + row8)
AND (cols.id - rows.id != col8 - row8)
) AS b7
WHERE cols.id != col8 AND rows.id != row8
AND cols.id != col7 AND rows.id != row7
AND (cols.id + rows.id != col8 + row8) AND (cols.id - rows.id != col8 - row8)
AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
) AS b6
WHERE cols.id != col8 AND rows.id != row8
AND cols.id != col7 AND rows.id != row7
AND cols.id != col6 AND rows.id != row6
AND (cols.id + rows.id != col8 + row8) AND (cols.id - rows.id != col8 - row8)
AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
AND (cols.id + rows.id != col6 + row6) AND (cols.id - rows.id != col6 - row6)
) AS b5
WHERE cols.id != col8 AND rows.id != row8
AND cols.id != col7 AND rows.id != row7
AND cols.id != col6 AND rows.id != row6
AND cols.id != col5 AND rows.id != row5
AND (cols.id + rows.id != col8 + row8) AND (cols.id - rows.id != col8 - row8)
AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
AND (cols.id + rows.id != col6 + row6) AND (cols.id - rows.id != col6 - row6)
AND (cols.id + rows.id != col5 + row5) AND (cols.id - rows.id != col5 - row5)
) AS b4
WHERE cols.id != col8 AND rows.id != row8
AND cols.id != col7 AND rows.id != row7
AND cols.id != col6 AND rows.id != row6
AND cols.id != col5 AND rows.id != row5
AND cols.id != col4 AND rows.id != row4
AND (cols.id + rows.id != col8 + row8) AND (cols.id - rows.id != col8 - row8)
AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
AND (cols.id + rows.id != col6 + row6) AND (cols.id - rows.id != col6 - row6)
AND (cols.id + rows.id != col5 + row5) AND (cols.id - rows.id != col5 - row5)
AND (cols.id + rows.id != col4 + row4) AND (cols.id - rows.id != col4 - row4)
) AS b3
WHERE cols.id != col8 AND rows.id != row8
AND cols.id != col7 AND rows.id != row7
AND cols.id != col6 AND rows.id != row6
AND cols.id != col5 AND rows.id != row5
AND cols.id != col4 AND rows.id != row4
AND cols.id != col3 AND rows.id != row3
AND cols.id != col2 AND rows.id != row2
AND (cols.id + rows.id != col8 + row8) AND (cols.id - rows.id != col8 - row8)
AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
AND (cols.id + rows.id != col6 + row6) AND (cols.id - rows.id != col6 - row6)
AND (cols.id + rows.id != col5 + row5) AND (cols.id - rows.id != col5 - row5)
AND (cols.id + rows.id != col4 + row4) AND (cols.id - rows.id != col4 - row4)
AND (cols.id + rows.id != col3 + row3) AND (cols.id - rows.id != col3 - row3)
AND (cols.id + rows.id != col2 + row2) AND (cols.id - rows.id != col2 - row2)
LIMIT 1337; --Arbitrary, you can let yours go all day.
</source>

''Commentary:'' I realize that this could be more elegant by trimming out the hard-coded values, and that I could set it up for N queens, but I got excited when it ran for 8. I wrote a nonrecursive brute-force version that ended as expected, with me sighing and restarting Postgres. If I go and edit it, it'll certainly be to put the results in a human-readable form. Because it's really cool, but isn't smart enough to choose good placements ahead of time, I give myself 7 Queens out of a possible 8. Also, update since 2007, ChatGPT will just do this for you.

@@ Line 1: / Line 1: @@
-== SQL Eight Queens in SQL ==
+<pre>
-'''Create the board:'''
+-- Create the board:
 CREATE TABLE rows (
    id integer PRIMARY KEY
 );
-INSERT INTO rows (id) VALUES (1),(2),(3),(4),(5),(6),(7),(8);
+INSERT INTO rows (id) VALUES (1), (2), (3), (4), (5), (6), (7), (8);
 CREATE TABLE cols (
    id integer PRIMARY KEY
 );
-INSERT INTO cols (id) VALUES (1),(2),(3),(4),(5),(6),(7),(8);
+INSERT INTO cols (id) VALUES (1), (2), (3), (4), (5), (6), (7), (8);
-'''Get a set of queens:'''
+-- Get a set of queens:
 SELECT
    cols.id AS col1, rows.id AS row1,
@@ Line 58: / Line 56: @@
              col8, row8,
              rows.id AS row7, cols.id AS col7
-             FROM rows, cols, (SELECT
+             FROM rows, cols
-              rows.id AS row8, cols.id AS col8
+             WHERE cols.id != col8 AND rows.id != row8 -- This checks rook moves
-              FROM rows, cols)
+             AND (cols.id + rows.id != col8 + row8) -- This checks bishop moves
              AND (cols.id - rows.id != col8 - row8)
-            ) AS b7
+          ) AS b7
            WHERE cols.id != col8 AND rows.id != row8
            AND cols.id != col7 AND rows.id != row7
            AND (cols.id + rows.id != col8 + row8) AND (cols.id - rows.id != col8 - row8)
            AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
-          ) AS b6
+        ) AS b6
          WHERE cols.id != col8 AND rows.id != row8
          AND cols.id != col7 AND rows.id != row7
@@ Line 77: / Line 72: @@
          AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
          AND (cols.id + rows.id != col6 + row6) AND (cols.id - rows.id != col6 - row6)
-        ) AS b5
+      ) AS b5
        WHERE cols.id != col8 AND rows.id != row8
        AND cols.id != col7 AND rows.id != row7
@@ Line 86: / Line 81: @@
        AND (cols.id + rows.id != col6 + row6) AND (cols.id - rows.id != col6 - row6)
        AND (cols.id + rows.id != col5 + row5) AND (cols.id - rows.id != col5 - row5)
-      ) AS b4
+    ) AS b4
      WHERE cols.id != col8 AND rows.id != row8
      AND cols.id != col7 AND rows.id != row7
@@ Line 97: / Line 92: @@
      AND (cols.id + rows.id != col5 + row5) AND (cols.id - rows.id != col5 - row5)
      AND (cols.id + rows.id != col4 + row4) AND (cols.id - rows.id != col4 - row4)
-    ) AS b3
+  ) AS b3
    WHERE cols.id != col8 AND rows.id != row8
    AND cols.id != col7 AND rows.id != row7
@@ Line 104: / Line 99: @@
    AND cols.id != col4 AND rows.id != row4
    AND cols.id != col3 AND rows.id != row3
    AND (cols.id + rows.id != col8 + row8) AND (cols.id - rows.id != col8 - row8)
    AND (cols.id + rows.id != col7 + row7) AND (cols.id - rows.id != col7 - row7)
@@ Line 111: / Line 105: @@
    AND (cols.id + rows.id != col4 + row4) AND (cols.id - rows.id != col4 - row4)
    AND (cols.id + rows.id != col3 + row3) AND (cols.id - rows.id != col3 - row3)
-  AND (cols.id + rows.id != col2 + row2) AND (cols.id - rows.id != col2 - row2)
+) AS b2
-LIMIT 1337;  --Arbitrary, you can let yours go all day.
+WHERE cols.id != col8 AND rows.id != row8
-</source>
+AND cols.id != col7 AND rows.id != row7
+AND cols.id != col6 AND rows.id != row6
-''Commentary:'' I realize that this could be more elegant by trimming out the hard-coded values, and that I could set it up for N queens, but I got excited when it ran for 8. I wrote a nonrecursive brute-force version that ended as expected, with me sighing and restarting Postgres. If I go and edit it, it'll certainly be to put the results in a human-readable form. Because it's really cool, but isn't smart enough to choose good placements ahead of time, I give myself 7 Queens out of a possible 8. Also, update since 2007, ChatGPT will just do this for you.
+AND cols.id != col5 AND rows.id != row5