关联查询优化以及join底层原理_join 内层嵌套循环-优快云博客

本文链接：https://blog.youkuaiyun.com/m0_69766497/article/details/127511369

本文详细探讨了MySQL中的外连接和内连接，分析了JOIN的三种底层原理：简单嵌套循环连接（SNLJ）、索引嵌套循环连接（INLJ）和块嵌套循环连接（BNLJ），并给出了优化策略，包括选择合适的驱动表、增加索引、调整join_buffer_size等。同时，文章提到了MySQL8.0版本开始引入的Hash Join，作为大数据集连接的优化方式。

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第一阶段：简单嵌套循环连接（SNLJ）编辑

第二阶段：索引嵌套循环连接（INLJ）

第三阶段：块钱套循环连接（BNLJ）

02、 join小结

1、外连接

数据准备

CREATE TABLE IF NOT EXISTS `type` (
`id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`card` INT(10) UNSIGNED NOT NULL,
PRIMARY KEY (`id`)
);
#图书
CREATE TABLE IF NOT EXISTS `book` (
`bookid` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`card` INT(10) UNSIGNED NOT NULL,
PRIMARY KEY (`bookid`)
);

#向分类表中添加20条记录
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO TYPE(card) VALUES(FLOOR(1 + (RAND() * 20)));

#向图书表中添加20条记录
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));
INSERT INTO book(card) VALUES(FLOOR(1 + (RAND() * 20)));

测试语句如下

EXPLAIN SELECT SQL_NO_CACHE * FROM `type` LEFT JOIN book ON type.card = book.card;

#给book表中的card字段添加索引
CREATE INDEX Y ON book(card);

EXPLAIN SELECT SQL_NO_CACHE * FROM `type` LEFT JOIN book ON type.card = book.card;

#给