006--Explain实战详解：table分析

1.table展示数据来自哪一张表

mysql> EXPLAIN SELECT t1.id from t1,t3,t2  where t1.id = t3.id and t3.id = t2.id and t2.id = 1;
+----+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra                          |
+----+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+
|  1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL |    3 | Using where                    |
|  1 | SIMPLE      | t3    | ALL  | NULL          | NULL | NULL    | NULL |    3 | Using where; Using join buffer |
|  1 | SIMPLE      | t2    | ALL  | NULL          | NULL | NULL    | NULL |    3 | Using where; Using join buffer |
+----+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+

mysql> EXPLAIN SELECT t1.id from t1,t2,t3  where t1.id = t3.id and t3.id = t2.id and t2.id = 1;
+----+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra                          |
+----+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+
|  1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL |    3 | Using where                    |
|  1 | SIMPLE      | t2    | ALL  | NULL          | NULL | NULL    | NULL |    3 | Using where; Using join buffer |
|  1 | SIMPLE      | t3    | ALL  | NULL          | NULL | NULL    | NULL |    3 | Using where; Using join buffer |
+----+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+

2.table使用总结：

• table意义：展示数据来自哪一张表
• table作用：数据源

3.执行的SQL文件

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for t1
-- ----------------------------
DROP TABLE IF EXISTS `t1`;
CREATE TABLE `t1` (
  `id` int(5) DEFAULT NULL,
  `name` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of t1
-- ----------------------------
INSERT INTO `t1` VALUES ('1', 'downeyjr_1');
INSERT INTO `t1` VALUES ('2', 'downeyjr_2');
INSERT INTO `t1` VALUES ('3', 'downeyjr_3');

-- ----------------------------
-- Table structure for t2
-- ----------------------------
DROP TABLE IF EXISTS `t2`;
CREATE TABLE `t2` (
  `id` int(5) DEFAULT NULL,
  `name` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of t2
-- ----------------------------
INSERT INTO `t2` VALUES ('1', 'downeyjr_1');
INSERT INTO `t2` VALUES ('2', 'downeyjr_2');
INSERT INTO `t2` VALUES ('3', 'downeyjr_3');

-- ----------------------------
-- Table structure for t3
-- ----------------------------
DROP TABLE IF EXISTS `t3`;
CREATE TABLE `t3` (
  `id` int(5) DEFAULT NULL,
  `name` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of t3
-- ----------------------------
INSERT INTO `t3` VALUES ('1', 'downeyjr_1');
INSERT INTO `t3` VALUES ('2', 'downeyjr_2');
INSERT INTO `t3` VALUES ('3', 'downeyjr_3');