Commit 7abba3b0 authored by holyfoot/hf@mysql.com/hfmain.(none)'s avatar holyfoot/hf@mysql.com/hfmain.(none)
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Bug #32942 now() - interval '7200' second NOT pre-calculated, causing "full table scan" 

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.
parent 8be07b88

mysql-test/r/select.result

+21 −0
Original line number Diff line number Diff line
@@ -4328,4 +4328,25 @@ SELECT * FROM t1 WHERE c1 > NULL + 1; 
c1

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

mysql-test/t/select.test

+18 −0
Original line number Diff line number Diff line
@@ -3672,4 +3672,22 @@ DROP TABLE t1; 


--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

sql/sql_select.cc

+1 −1
Original line number Diff line number Diff line
@@ -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.

      */

      if (not_used_in_distinct && found_records != join->found_records)

        return NESTED_LOOP_OK;

        return NESTED_LOOP_NO_MORE_ROWS;

    }

    else

      join_tab->read_record.file->unlock_row();