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Bug #21456: SELECT DISTINCT(x) produces incorrect results when using order by

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GROUP BY/DISTINCT pruning optimization must be done before ORDER BY 
optimization because ORDER BY may be removed when GROUP BY/DISTINCT
sorts as a side effect, e.g. in 
  SELECT DISTINCT <non-key-col>,<pk> FROM t1
  ORDER BY <non-key-col> DISTINCT
must be removed before ORDER BY as if done the other way around
it will remove both.


mysql-test/r/distinct.result:
  Test for BUG#21456.
mysql-test/t/distinct.test:
  Test for BUG#21456.
sql/sql_select.cc:
  Bug #21456: SELECT DISTINCT(x) produces incorrect results when using order by
  
  GROUP BY/DISTINCT pruning optimization must be done before ORDER BY 
  optimization because ORDER BY may be removed when GROUP BY/DISTINCT
  sorts as a side effect.
This commit is contained in:
unknown
2006-08-23 16:46:57 +03:00
parent bfdbb780c2
commit 2baf2fdf13
3 changed files with 52 additions and 30 deletions
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11
mysql-test/r/distinct.result
View File

@ -555,3 +555,14 @@ EXPLAIN SELECT DISTINCT a,b,d FROM t2 GROUP BY c,b,d;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 3
DROP TABLE t1,t2;
CREATE TABLE t1 (a int primary key, b int);
INSERT INTO t1 (a,b) values (1,1), (2,3), (3,2);
explain SELECT DISTINCT a, b FROM t1 ORDER BY b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
SELECT DISTINCT a, b FROM t1 ORDER BY b;
a b
1 1
3 2
2 3
DROP TABLE t1;

11
mysql-test/t/distinct.test
View File

@ -378,4 +378,15 @@ EXPLAIN SELECT DISTINCT a,b,d FROM t2 GROUP BY c,b,d;
DROP TABLE t1,t2;
#
# Bug 21456: SELECT DISTINCT(x) produces incorrect results when using order by
#
CREATE TABLE t1 (a int primary key, b int);
INSERT INTO t1 (a,b) values (1,1), (2,3), (3,2);
explain SELECT DISTINCT a, b FROM t1 ORDER BY b;
SELECT DISTINCT a, b FROM t1 ORDER BY b;
DROP TABLE t1;
# End of 4.1 tests