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Bug #44139: Table scan when NULL appears in IN clause

Browse Source 
SELECT ... WHERE ... IN (NULL, ...) does full table scan,
even if the same query without the NULL uses efficient range scan.

The bugfix for the bug 18360 introduced an optimization:
if
  1) all right-hand arguments of the IN function are constants
  2) result types of all right argument items are compatible
     enough to use the same single comparison function to
     compare all of them to the left argument,

then

  we can convert the right-hand list of constant items to an array
  of equally-typed constant values for the further
  QUICK index access etc. (see Item_func_in::fix_length_and_dec()).

The Item_null constant item objects have STRING_RESULT
result types, so, as far as Item_func_in::fix_length_and_dec()
is aware of NULLs in the right list, this improvement efficiently
optimizes IN function calls with a mixed right list of NULLs and
string constants. However, the optimization doesn't affect mixed
lists of NULLs and integers, floats etc., because there is no
unique common comparator.


New optimization has been added to ignore the result type
of NULL constants in the static analysis of mixed right-hand lists.
This is safe, because at the execution phase we care about
presence of NULLs anyway.

1. The collect_cmp_types() function has been modified to optionally
   ignore NULL constants in the item list.
2. NULL-skipping code of the Item_func_in::fix_length_and_dec()
   function has been modified to work not only with in_string
   vectors but with in_vectors of other types.
This commit is contained in:
Gleb Shchepa
2009-10-05 10:27:36 +05:00
parent 5992e70623
commit 2b78dbff54
3 changed files with 241 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

85
mysql-test/t/func_in.test
View File

@ -456,4 +456,89 @@ SELECT SUM( DISTINCT e ) FROM t1 GROUP BY b,c,d HAVING (b,c,d) IN
((AVG( 1 ), 1 + c, 1 + d), (AVG( 1 ), 2 + c, 2 + d));
DROP TABLE t1;
--echo #
--echo # Bug #44139: Table scan when NULL appears in IN clause
--echo #
--disable_warnings
CREATE TABLE t1 (
c_int INT NOT NULL,
c_decimal DECIMAL(5,2) NOT NULL,
c_float FLOAT(5, 2) NOT NULL,
c_bit BIT(10) NOT NULL,
c_date DATE NOT NULL,
c_datetime DATETIME NOT NULL,
c_timestamp TIMESTAMP NOT NULL,
c_time TIME NOT NULL,
c_year YEAR NOT NULL,
c_char CHAR(10) NOT NULL,
INDEX(c_int), INDEX(c_decimal), INDEX(c_float), INDEX(c_bit), INDEX(c_date),
INDEX(c_datetime), INDEX(c_timestamp), INDEX(c_time), INDEX(c_year),
INDEX(c_char));
INSERT INTO t1 (c_int) VALUES (1), (2), (3), (4), (5);
INSERT INTO t1 (c_int) SELECT 0 FROM t1;
INSERT INTO t1 (c_int) SELECT 0 FROM t1;
--enable_warnings
EXPLAIN SELECT * FROM t1 WHERE c_int IN (1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_int IN (NULL, 1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_int IN (1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_int IN (1, NULL, 2, NULL, 3, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_int IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_int IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_decimal IN (1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_decimal IN (NULL, 1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_decimal IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_decimal IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_float IN (1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_float IN (NULL, 1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_float IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_float IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_bit IN (1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_bit IN (NULL, 1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_bit IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_bit IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_date
IN ('2009-09-01', '2009-09-02', '2009-09-03');
EXPLAIN SELECT * FROM t1 WHERE c_date
IN (NULL, '2009-09-01', '2009-09-02', '2009-09-03');
EXPLAIN SELECT * FROM t1 WHERE c_date IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_date IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_datetime
IN ('2009-09-01 00:00:01', '2009-09-02 00:00:01', '2009-09-03 00:00:01');
EXPLAIN SELECT * FROM t1 WHERE c_datetime
IN (NULL, '2009-09-01 00:00:01', '2009-09-02 00:00:01', '2009-09-03 00:00:01');
EXPLAIN SELECT * FROM t1 WHERE c_datetime IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_datetime IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_timestamp
IN ('2009-09-01 00:00:01', '2009-09-01 00:00:02', '2009-09-01 00:00:03');
EXPLAIN SELECT * FROM t1 WHERE c_timestamp
IN (NULL, '2009-09-01 00:00:01', '2009-09-01 00:00:02', '2009-09-01 00:00:03');
EXPLAIN SELECT * FROM t1 WHERE c_timestamp IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_timestamp IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_year IN (1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_year IN (NULL, 1, 2, 3);
EXPLAIN SELECT * FROM t1 WHERE c_year IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_year IN (NULL, NULL);
EXPLAIN SELECT * FROM t1 WHERE c_char IN ('1', '2', '3');
EXPLAIN SELECT * FROM t1 WHERE c_char IN (NULL, '1', '2', '3');
EXPLAIN SELECT * FROM t1 WHERE c_char IN (NULL);
EXPLAIN SELECT * FROM t1 WHERE c_char IN (NULL, NULL);
DROP TABLE t1;
--echo #
--echo End of 5.1 tests