After reading one of the recent posts from Gobi [EMAIL PROTECTED]
I took his successful query and modified it for one of my tables. It indeed
produce the correct result, but in the process raised some questions.
1. Why do list_ID and acct_ID not have to be qualified with a table
name or alias?
mysql> SELECT list_ID, list_Name, acct_ID, list_Qty
-> FROM lists
-> INNER JOIN (SELECT acct_ID, max(list_ID) AS list_ID
-> FROM lists
-> GROUP BY acct_id
-> ) AS t
-> USING (acct_ID, list_ID)
-> WHERE list_Active = 'Yes'
-> AND cpny_ID = 'RER1'
-> LIMIT 100,10;
+---------+----------------------------+---------+----------+
| list_ID | list_Name | acct_ID | list_Qty |
+---------+----------------------------+---------+----------+
| 3 | Farm | BA8M | 0 |
| 10 | Woodbury | BA8Y | 100 |
| 2 | Brookview Heights 03-23-04 | BA9O | 278 |
| 4 | Magnet Mailing | BABA | 250 |
| 2 | Fall Back | BABM | 223 |
| 1 | Contact list | BACF | 71 |
| 4 | Friends/Family | BAE2 | 10 |
| 1 | St. Michael | BAE7 | 139 |
| 2 | JS Prospects | BAE8 | 196 |
| 1 | Home Focus | BAE9 | 55 |
+---------+----------------------------+---------+----------+
10 rows in set (0.03 sec)
2. While the subselect does work, it appears to generate a cartesian
product. Initial guess with 5.0 and stored procedures would be that
CREATING TEMPORARY TABLE
INSERT max values in temporary
SELECT from main table joined with temporary
would run faster and still allow this to be done with 1 statement.
However, even though the explains would indicate that this was so {23508 *
7354 rows for subselect VS 6060 rows for temporary table}
actual times are {0.03 for subselect VS 0.19 for temporary table} . After doing
some playing, it is the INSERT into temporary that adds the
time even though the table was memory resident. Trying a similar request on a
table with 3.5M rows still favors the subselect
{27.50 sec for subselect VS 1 min 13.91 sec for temporary table}.
Has EXPLAIN just not caught up with SUBSELECT logic or is there something else
going on?
mysql> EXPLAIN
-> SELECT list_ID, list_Name, acct_ID, list_Qty
-> FROM lists
-> INNER JOIN (SELECT acct_ID, max(list_ID) AS list_ID
-> FROM lists
-> GROUP BY acct_id
-> ) AS t
-> USING (acct_ID, list_ID)
-> WHERE list_Active = 'Yes'
-> AND cpny_ID = 'RER1'
-> LIMIT 100,10;
+----+-------------+------------+--------+----------------------+---------+---------+---------------------+-------+-------------+
| id | select_type | table | type | possible_keys | key |
key_len | ref | rows | Extra |
+----+-------------+------------+--------+----------------------+---------+---------+---------------------+-------+-------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL |
NULL | NULL | 7354 | |
| 1 | PRIMARY | lists | eq_ref | PRIMARY,acct_list_ID | PRIMARY |
6 | t.acct_ID,t.list_ID | 1 | Using where |
| 2 | DERIVED | lists | index | NULL | PRIMARY |
6 | NULL | 23508 | Using index |
+----+-------------+------------+--------+----------------------+---------+---------+---------------------+-------+-------------+
3 rows in set (0.01 sec)
mysql> SELECT list_ID, list_Name, acct_ID, list_Qty
-> FROM lists
-> INNER JOIN (SELECT acct_ID, max(list_ID) AS list_ID
-> FROM lists
-> GROUP BY acct_id
-> ) AS t
-> USING (acct_ID, list_ID)
-> WHERE list_Active = 'Yes'
-> AND cpny_ID = 'RER1'
-> LIMIT 100,10;
+---------+----------------------------+---------+----------+
| list_ID | list_Name | acct_ID | list_Qty |
+---------+----------------------------+---------+----------+
| 3 | Farm | BA8M | 0 |
| 10 | Woodbury | BA8Y | 100 |
| 2 | Brookview Heights 03-23-04 | BA9O | 278 |
| 4 | Magnet Mailing | BABA | 250 |
| 2 | Fall Back | BABM | 223 |
| 1 | Contact list | BACF | 71 |
| 4 | Friends/Family | BAE2 | 10 |
| 1 | St. Michael | BAE7 | 139 |
| 2 | JS Prospects | BAE8 | 196 |
| 1 | Home Focus | BAE9 | 55 |
+---------+----------------------------+---------+----------+
10 rows in set (0.03 sec)
mysql> CREATE TEMPORARY TABLE `max_list_id` (
-> `acct_ID` CHAR (4) NOT NULL,
-> `list_ID` INT UNSIGNED DEFAULT '0' NOT NULL,
-> PRIMARY KEY(`acct_ID`)
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> INSERT INTO max_list_ID
-> SELECT acct_ID, max(list_ID) AS list_ID
-> FROM lists
-> GROUP BY acct_id;
Query OK, 7354 rows affected (0.23 sec)
Records: 7354 Duplicates: 0 Warnings: 0
mysql> EXPLAIN
-> SELECT l.list_ID, l.list_Name, l.acct_ID, l.list_Qty
-> FROM lists AS l
-> INNER JOIN max_list_id AS t
-> USING (acct_ID, list_ID)
-> WHERE l.list_Active = 'Yes'
-> AND l.cpny_ID = 'RER1'
-> LIMIT 100,10;
+----+-------------+-------+--------+----------------------+--------------+---------+---------------------+------+-------------+
| id | select_type | table | type | possible_keys | key |
key_len | ref | rows | Extra |
+----+-------------+-------+--------+----------------------+--------------+---------+---------------------+------+-------------+
| 1 | SIMPLE | l | ref | PRIMARY,acct_list_ID | acct_list_ID |
4 | const | 6060 | Using where |
| 1 | SIMPLE | t | eq_ref | PRIMARY | PRIMARY |
4 | mailprint.l.acct_ID | 1 | Using where |
+----+-------------+-------+--------+----------------------+--------------+---------+---------------------+------+-------------+
2 rows in set (0.00 sec)
mysql> SELECT l.list_ID, l.list_Name, l.acct_ID, l.list_Qty
-> FROM lists AS l
-> INNER JOIN max_list_id AS t
-> USING (acct_ID, list_ID)
-> WHERE l.list_Active = 'Yes'
-> AND l.cpny_ID = 'RER1'
-> LIMIT 100,10;
+---------+----------------------------+---------+----------+
| list_ID | list_Name | acct_ID | list_Qty |
+---------+----------------------------+---------+----------+
| 3 | Farm | BA8M | 0 |
| 10 | Woodbury | BA8Y | 100 |
| 2 | Brookview Heights 03-23-04 | BA9O | 278 |
| 4 | Magnet Mailing | BABA | 250 |
| 2 | Fall Back | BABM | 223 |
| 1 | Contact list | BACF | 71 |
| 4 | Friends/Family | BAE2 | 10 |
| 1 | St. Michael | BAE7 | 139 |
| 2 | JS Prospects | BAE8 | 196 |
| 1 | Home Focus | BAE9 | 55 |
+---------+----------------------------+---------+----------+
10 rows in set (0.00 sec)
mysql> DROP TABLE max_list_id;
Query OK, 0 rows affected (0.01 sec)
mysql> DELIMITER //
mysql> DROP PROCEDURE max_ID//
Query OK, 0 rows affected (0.20 sec)
mysql> CREATE PROCEDURE max_ID ()
-> BEGIN
-> CREATE TEMPORARY TABLE `max_list_id` (
-> `acct_ID` CHAR (4) NOT NULL,
-> `list_ID` INT UNSIGNED DEFAULT '0' NOT NULL,
-> PRIMARY KEY(`acct_ID`)
-> );
->
-> INSERT INTO max_list_ID
-> SELECT acct_ID, max(list_ID) AS list_ID
-> FROM lists
-> GROUP BY acct_id;
->
-> EXPLAIN
-> SELECT l.list_ID, l.list_Name, l.acct_ID, l.list_Qty
-> FROM lists AS l
-> INNER JOIN max_list_id AS t
-> USING (acct_ID, list_ID)
-> WHERE l.list_Active = 'Yes'
-> AND l.cpny_ID = 'RER1'
-> LIMIT 100,10;
->
-> DROP TABLE max_list_id;
-> END; //
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER ;
mysql> CALL max_ID();
+----+-------------+-------+--------+----------------------+--------------+---------+---------------------+------+-------------+
| id | select_type | table | type | possible_keys | key |
key_len | ref | rows | Extra |
+----+-------------+-------+--------+----------------------+--------------+---------+---------------------+------+-------------+
| 1 | SIMPLE | l | ref | PRIMARY,acct_list_ID | acct_list_ID |
4 | const | 6060 | Using where |
| 1 | SIMPLE | t | eq_ref | PRIMARY | PRIMARY |
4 | mailprint.l.acct_ID | 1 | Using where |
+----+-------------+-------+--------+----------------------+--------------+---------+---------------------+------+-------------+
2 rows in set (0.20 sec)
Query OK, 0 rows affected (0.20 sec)
mysql> DELIMITER //
mysql>
mysql> DROP PROCEDURE max_ID//
Query OK, 0 rows affected (0.02 sec)
mysql> CREATE PROCEDURE max_ID ()
-> BEGIN
-> CREATE TEMPORARY TABLE `max_list_id` (
-> `acct_ID` CHAR (4) NOT NULL,
-> `list_ID` INT UNSIGNED DEFAULT '0' NOT NULL,
-> PRIMARY KEY(`acct_ID`)
-> );
->
-> INSERT INTO max_list_ID
-> SELECT acct_ID, max(list_ID) AS list_ID
-> FROM lists
-> GROUP BY acct_id;
->
-> SELECT l.list_ID, l.list_Name, l.acct_ID, l.list_Qty
-> FROM lists AS l
-> INNER JOIN max_list_id AS t
-> USING (acct_ID, list_ID)
-> WHERE l.list_Active = 'Yes'
-> AND l.cpny_ID = 'RER1'
-> LIMIT 100,10;
->
-> DROP TABLE max_list_id;
-> END; //
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> DELIMITER ;
mysql>
mysql> CALL max_ID();
+---------+----------------------------+---------+----------+
| list_ID | list_Name | acct_ID | list_Qty |
+---------+----------------------------+---------+----------+
| 3 | Farm | BA8M | 0 |
| 10 | Woodbury | BA8Y | 100 |
| 2 | Brookview Heights 03-23-04 | BA9O | 278 |
| 4 | Magnet Mailing | BABA | 250 |
| 2 | Fall Back | BABM | 223 |
| 1 | Contact list | BACF | 71 |
| 4 | Friends/Family | BAE2 | 10 |
| 1 | St. Michael | BAE7 | 139 |
| 2 | JS Prospects | BAE8 | 196 |
| 1 | Home Focus | BAE9 | 55 |
+---------+----------------------------+---------+----------+
10 rows in set (0.19 sec)
Query OK, 0 rows affected (0.19 sec)
mysql>
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