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MySQL 5.6 MRR的存储过程完美诠释 MySQL 5.6 即将发布， 5.6对优化器方面做了诸多优化。 我这次主要解释MRR（MULTI-RANGE-READ）。 我用存储过程解释了这一过程的改变。大家细心体会去吧。我们针对语句：[sql] select log_time from person where nick_name = 'Lucy'; 表结构为：[sql] CREATE TABLE `person` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `nick_name` varchar(40) NOT NULL, `log_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`id`), KEY `idx_nick_name` (`nick_name`) ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1 首先是MySQL 5.5.[sql] DELIMITER $$ USE `ytt`$$ DROP PROCEDURE IF EXISTS `sp_range_scan5_5`$$ CREATE DEFINER=`admin`@`%` PROCEDURE `sp_range_scan5_5`() BEGIN -- Sample sql statement is below. -- select log_time from person where nick_name = 'Lucy'; DECLARE i INT UNSIGNED DEFAULT 0; DECLARE cnt INT UNSIGNED DEFAULT 0; SET @result = ''; SELECT COUNT(1) INTO cnt FROM person WHERE nick_name = 'Lucy'; loop1:WHILE i < cnt DO SET @stmt = CONCAT('select id into @v_id from person where nick_name = ''Lucy'' order by nick_name asc limit ',i,',1'); PREPARE s1 FROM @stmt; EXECUTE s1; SET @result = CONCAT(@result,'select log_time from person where id = @v_id'); SET @result = CONCAT(@result,' union all '); SET i = i + 1; END WHILE loop1; SET @result = SUBSTR(@result,1,CHAR_LENGTH(@result)-CHAR_LENGTH(' union all ')); PREPARE s1 FROM @result; EXECUTE s1; DROP PREPARE s1; SET @result = NULL; END$$ DELIMITER ; 下来是MySQL 5.6.[sql] DELIMITER $$ USE `ytt`$$ DROP PROCEDURE IF EXISTS `sp_range_scan5_6`$$ CREATE DEFINER=`admin`@`%` PROCEDURE `sp_range_scan5_6`() BEGIN -- Sample sql statement is below. -- select log_time from person where nick_name = 'Lucy'; DECLARE i INT UNSIGNED DEFAULT 0; DECLARE cnt INT UNSIGNED DEFAULT 0; DECLARE ids TEXT; SET ids = ''; SELECT COUNT(1) INTO cnt FROM person WHERE nick_name = 'Lucy'; loop1:WHILE i < cnt DO SET @stmt = CONCAT('select id into @v_id from person where nick_name = ''Lucy'' order by nick_name asc limit ',i,',1'); PREPARE s1 FROM @stmt; EXECUTE s1; SET ids = CONCAT(ids,@v_id,','); SET i = i + 1; END WHILE loop1; SET ids = CONCAT('(',SUBSTR(ids,1,CHAR_LENGTH(ids)-1),')'); SET @result = CONCAT('select log_time from person where id in',ids); PREPARE s1 FROM @result; EXECUTE s1; DROP PREPARE s1; SET @result = NULL; END$$ DELIMITER ;
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