关于MySQL的一些优化（单表访问）

以此表为例

CREATE TABLE `single_table`  (
  `id` int NOT NULL AUTO_INCREMENT,
  `key1` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  `key2` int NULL DEFAULT NULL,
  `key3` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  `key_part1` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  `key_part2` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  `key_part3` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  `common_field` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  INDEX `idx_key1`(`key1`) USING BTREE,
  UNIQUE INDEX `idx_key2`(`key2`) USING BTREE,
  INDEX `idx_key3`(`key3`) USING BTREE,
  INDEX `idx_p1_p2_p3`(`key_part1`, `key_part2`, `key_part3`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;

const

select * from single_table where id = 143

上面这条SQL语句会直接利用主键值在聚簇索引中定位对应的用户记录