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Bug #32942 now() - interval '7200' second NOT pre-calculated, causing "full table scan"

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Problem is not about intervals and doesn't actually cause 'full table scan'.
We have an optimization for DISTINCT when we have
'DISTINCT field_from_first_join_table' we don't need to read all the
rows from the JOIN-ed table if we found one conforming row.
It stopped working in 5.0 as we return NESTED_LOOP_OK if we came upon
that case in the evaluate_join_record() and that doesn't break the
recordreading loop in sub_select().

Fixed by returning NESTED_LOOP_NO_MORE_ROWS in this case.


mysql-test/r/select.result:
  Bug #32942 now() - interval '7200' second is NOT pre-calculated, causing "full table scan".
  
  test result
mysql-test/t/select.test:
  Bug #32942 now() - interval '7200' second is NOT pre-calculated, causing "full table scan"
  
  test case
sql/sql_select.cc:
  Bug #32942 now() - interval '7200' second NOT pre-calculated, causing "full table scan"
  
  return NESTED_LOOP_NO_MORE_ROWS when we don't need to read rows from
  this table anymore
This commit is contained in:
unknown
2008-02-17 15:48:17 +04:00
parent 12504d906b
commit d6be1a9b95
3 changed files with 40 additions and 1 deletions
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21
mysql-test/r/select.result
View File

@ -4328,4 +4328,25 @@ SELECT * FROM t1 WHERE c1 > NULL + 1;
c1 c1
DROP TABLE t1; DROP TABLE t1;
CREATE TABLE t1 (a INT, b INT);
CREATE TABLE t2 (a INT, c INT, KEY(a));
INSERT INTO t1 VALUES (1, 1), (2, 2);
INSERT INTO t2 VALUES (1, 1), (1, 2), (1, 3), (1, 4), (1, 5),
(2, 1), (2, 2), (2, 3), (2, 4), (2, 5),
(3, 1), (3, 2), (3, 3), (3, 4), (3, 5),
(4, 1), (4, 2), (4, 3), (4, 4), (4, 5);
FLUSH STATUS;
SELECT DISTINCT b FROM t1 LEFT JOIN t2 USING(a) WHERE c <= 3;
b
1
2
SHOW STATUS LIKE 'Handler_read%';
Variable_name Value
Handler_read_first 0
Handler_read_key 2
Handler_read_next 0
Handler_read_prev 0
Handler_read_rnd 0
Handler_read_rnd_next 6
DROP TABLE t1, t2;
End of 5.0 tests End of 5.0 tests

18
mysql-test/t/select.test
View File

@ -3672,4 +3672,22 @@ DROP TABLE t1;
--echo --echo
#
# Bug #32942 now() - interval '7200' second is NOT pre-calculated, causing "full table scan"
#
CREATE TABLE t1 (a INT, b INT);
CREATE TABLE t2 (a INT, c INT, KEY(a));
INSERT INTO t1 VALUES (1, 1), (2, 2);
INSERT INTO t2 VALUES (1, 1), (1, 2), (1, 3), (1, 4), (1, 5),
(2, 1), (2, 2), (2, 3), (2, 4), (2, 5),
(3, 1), (3, 2), (3, 3), (3, 4), (3, 5),
(4, 1), (4, 2), (4, 3), (4, 4), (4, 5);
FLUSH STATUS;
SELECT DISTINCT b FROM t1 LEFT JOIN t2 USING(a) WHERE c <= 3;
SHOW STATUS LIKE 'Handler_read%';
DROP TABLE t1, t2;
--echo End of 5.0 tests --echo End of 5.0 tests

2
sql/sql_select.cc
View File

@ -10791,7 +10791,7 @@ evaluate_join_record(JOIN *join, JOIN_TAB *join_tab,
we found a row, as no new rows can be added to the result. we found a row, as no new rows can be added to the result.
*/ */
if (not_used_in_distinct && found_records != join->found_records) if (not_used_in_distinct && found_records != join->found_records)
return NESTED_LOOP_OK; return NESTED_LOOP_NO_MORE_ROWS;
} }
else else
join_tab->read_record.file->unlock_row(); join_tab->read_record.file->unlock_row();