MySQL 模拟条件目录

           Table "ytt.girl1"
 Column |  Type   |     Modifiers      
--------+---------+--------------------
 id     | integer | not null
 rank   | integer | not null default 0
Indexes:
    "girl1_pkey" PRIMARY KEY, btree (id)
    "idx_girl1_rank" btree (rank) WHERE rank >= 10 AND rank   Index Scan using idx_girl1_rank on girl1  (cost=0.29..421.26 rows=232 width=8) (actual time=0.023..0.044 rows=20 loops=1)
         Index Cond: ((rank >= 20) AND (rank   Index Scan using idx_girl1_rank on girl1  (cost=0.28..513.44 rows=291 width=8) (actual time=0.033..0.061 rows=20 loops=1)
         Index Cond: ((rank >= 20) AND (rank <br><br><br>可以看出，在扫描的记录数以及时间上，条件索引的优势都很明显。<br><br><br>接下来，我们在MySQL 模拟下这样的过程。<br>由于MySQL 不支持这样的索引， 在SQL层面上，只能创建一个索引表来保存对应条件的主键以及索引键。<br><br><br><pre code_snippet_id="270930" snippet_file_name="blog_20140402_2_9214190" name="code" class="sql">ytt>show create table girl1_filtered_index;
+----------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table                | Create Table                                                                                                                                                                                 |
+----------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| girl1_filtered_index | CREATE TABLE `girl1_filtered_index` (
  `id` int(11) NOT NULL,
  `rank` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`),
  KEY `idx_rank` (`rank`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+----------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)






接下来，对基础表的更新操作做下修改，创建了三个触发器。
DELIMITER $$


USE `t_girl`$$


DROP TRIGGER /*!50032 IF EXISTS */ `filtered_insert`$$


CREATE
    /*!50017 DEFINER = 'root'@'localhost' */
    TRIGGER `filtered_insert` AFTER INSERT ON `girl1` 
    FOR EACH ROW BEGIN
	IF new.rank BETWEEN 10 AND 100 THEN
		INSERT INTO girl1_filtered_index VALUES (new.id,new.rank); 
	END IF;
	
    END;
$$


DELIMITER ;




DELIMITER $$


USE `t_girl`$$


DROP TRIGGER /*!50032 IF EXISTS */ `filtered_update`$$


CREATE
    /*!50017 DEFINER = 'root'@'localhost' */
    TRIGGER `filtered_update` AFTER UPDATE ON `girl1` 
    FOR EACH ROW BEGIN
	IF new.rank BETWEEN 10 AND 100 THEN
		REPLACE girl1_filtered_index VALUES (new.id,new.rank); 
	ELSE
		DELETE FROM girl1_filtered_index WHERE id = old.id;
	END IF;
    END;
$$


DELIMITER ;




DELIMITER $$


USE `t_girl`$$


DROP TRIGGER /*!50032 IF EXISTS */ `filtered_delete`$$


CREATE
    /*!50017 DEFINER = 'root'@'localhost' */
    TRIGGER `filtered_delete` AFTER DELETE ON `girl1` 
    FOR EACH ROW BEGIN
	DELETE FROM  girl1_filtered_index WHERE id = old.id;
    END;
$$


DELIMITER ;


OK，我们导入测试数据。
ytt>load data infile 'girl1.txt' into table girl1 fields terminated by ',';
Query OK, 100000 rows affected (1.05 sec)            
Records: 100000  Deleted: 0  Skipped: 0  Warnings: 0


ytt>select count(*) from girl1;
+----------+
| count(*) |
+----------+
|   100000 |
+----------+
1 row in set (0.04 sec)


ytt>select count(*) from girl1_filtered_index;
+----------+
| count(*) |
+----------+
|      640 |
+----------+
1 row in set (0.00 sec)

select a.id,a.rank from girl1 as a where a.id in (select b.id from girl1_filtered_index as b where b.rank between 20 and 60)  limit 20;