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This script
DROP TABLE IF EXISTS t1;
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CREATE TABLE t1 (a GEOMETRY NOT NULL, SPATIAL KEY(a)) ENGINE=MyISAM;
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INSERT INTO t1 VALUES (Point(1,2)),(Point(1,3));
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EXPLAIN SELECT * FROM t1 WHERE MBRINTERSECTS(a,Point(1,2));
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returns
+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
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| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
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+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
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| 1 | SIMPLE | t1 | range | a | a | 34 | NULL | 1 | Using where |
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+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
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which means range optimizer is used. So far so good.
Now if I change the order of the arguments:
EXPLAIN SELECT * FROM t1 WHERE MBRINTERSECTS(Point(1,2),a);
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it does not use the index any more:
+------+-------------+-------+------+---------------+------+---------+------+------+-------------+
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| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
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+------+-------------+-------+------+---------------+------+---------+------+------+-------------+
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| 1 | SIMPLE | t1 | ALL | a | NULL | NULL | NULL | 2 | Using where |
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+------+-------------+-------+------+---------------+------+---------+------+------+-------------+
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The same problem is repeatable with the precise function INTERSECTS().
Note, MBRINTERSECTS() and INTERSECTS() are symmetric operation, so the order of the arguments should not matter.
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