先在mysql中建个表:
CREATE TABLE `t_user` ( `id` int ( 6 ) NOT NULL AUTO_INCREMENT, `name` varchar ( 30 ) CHARACTER SET latin1 COLLATE latin1_swedish_ci NOT NULL , `age` int ( 4 ) NOT NULL DEFAULT 20 , `address` varchar ( 30 ) CHARACTER SET latin1 COLLATE latin1_swedish_ci NOT NULL default ‘‘ , `create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP , `version` int ( 4 ) NOT NULL DEFAULT 0 , PRIMARY KEY (`id`) USING BTREE , UNIQUE INDEX `idx_name`(`name`) USING BTREE , INDEX `idx_age_address`(`age`, `address`) USING BTREE ) ENGINE = InnoDB AUTO_INCREMENT = 15 CHARACTER SET = latin1 COLLATE = latin1_swedish_ci ROW_FORMAT = DYNAMIC;
这个DDL创建了3个B+tree索引,我都用黄色背景标出来了。现在开始使用explain对各种查询进行分析:
1、type = ALL 是全表扫描
EXPLAIN select * from t_user; -- 全表扫描
end.
mysql5.7版本的explain解析
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