Details
Description
CREATE OR REPLACE TABLE t1 (a VARCHAR(500) CHARACTER SET utf8mb4 COLLATE utf8mb4_danish_ci); |
INSERT INTO t1 VALUES ('aaaa'),('åå'); |
SELECT * FROM t1 WHERE a='aaaa'; |
+------+
|
| a |
|
+------+
|
| aaaa |
|
| åå |
|
+------+
|
Looks good so far. It returns two records, because in Danish collation 'å' is equal to 'aa'.
Now I join the table to itself:
SET join_cache_level=1; |
SELECT * FROM t1 NATURAL JOIN t1 t2; |
+------+
|
| a |
|
+------+
|
| aaaa |
|
| åå |
|
| aaaa |
|
| åå |
|
+------+
|
Looks good so far.
Now I enable the BNLH join:
SET join_cache_level=3; |
SELECT * FROM t1 NATURAL JOIN t1 t2; |
+------+
|
| a |
|
+------+
|
| aaaa |
|
| åå |
|
+------+
|
Half of the records disappeared. Looks wrong.
Attachments
Issue Links
- is duplicated by
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MDEV-34352 Execution time for Block Nested Loop Hash (BNLH) join with charset utf8mb4 is 7-20 times slower than with latin1
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- Closed
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- relates to
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MDEV-34232 Check performance of BNL-H vs MySQL's hash join
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- Open
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- Closed
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- Open
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